SOME EFFECTS OF CERTAIN GROWTH-REGULATING SUBSTANCES UPON PREMATURE SEEDING IN CABBAGE By Evon Lam ar Moore A THESIS Submitted to the School of Graduate Studies of Michigan State C ollege of A griculture and Applied Science in p artial fulfillm ent of the requirem ents for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1954 ProQuest Number: 10008684 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest, ProQuest 10008684 Published by ProQuest LLC (2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, MI 4 8 1 0 6 -1 3 4 6 acknow ledgem ents T h e au th o r acknow ledges with g ra titu d e th e kind and g e n ero u s a s s i s t a n c e of Dr* 5* H* W ittw er u n d e r w hose guidance th is w o rk was conducted* T hanks a r e e x p r e s s e d to Dr* R . L* C aro lu s who su g g ested th e p r o b le m , and to o th e r facu lty m e m b e r s of th e D e p a rtm e n ts of H o r tic u l tu r e , Botany, and Soils who aided th e w r i t e r d u rin g th e i n ­ v estig atio n s* A p p re c ia tio n is e x p r e s s e d to m e m b e r s of th e H o r tic u ltu r a l D e p a r tm e n t, M is s is s i p p i S tate College fo r t h e i r a s s is ta n c e * P ar­ t i c u l a r l y , Mr* W. S* A n derson fo r a d m in is tr a tiv e a s s i s t a n c e in getting th e study ap p roved as a statio n p ro je c t; Dr* W* F* Jenkins fo r s u g g e stio n s on th e m a n u s c r ip t; and to Mr* C. O* Box fo r d r a w ­ ings u s e d in F i g u r e s 4, 5 and 9* T h e a s s i s t a n c e and advice of Dr* W alter D r a p a la on s t a t i s ­ t i c a l p r o b le m s is acknowledged* T A B L E OF CONTENTS Page I. ACKNOWLEDGEMENTS ii II. TA BLE OF CONTENTS iii III. LIST OF FIGURES vi IV . LIST OF TABLES x V. V I. VII. VIII. IX . X. ABSTRACT x ii INTRODUCTION 1 LITERA TU RE REVIEW 5 GENERAL MATERIALS AND METHODS 22 TERMINOLOGY 24 EX PERIM EN T 1: The E ffect of 2 , 4 -D, C1PP, T1BA and NA C o n c e n tr a ­ tio n s on Growth and D evelopm ent of Cabbage U nder G re e n h o u s e Conditions A. B. X I. M a t e r i a l s and Methods R es u lts: 1. N oncold-Induced P la n ts 2. C old-Induced P la n ts 25 28 36 EXPERIM ENT 2: T h e E ffect of 2 ,4 - D , C1PP, TIB A and NA C oncen­ t r a t i o n s on th e Growth and D evelopm ent of W in tered O v er Cabbage A. B. X II. M a te r i a ls and Methods R e s u lts EXPERIM ENT 3: The E ffect of T im e of Application of 2 ,4 - D and C1PP on G row th and D evelopm ent of L a r g e , Medium and iii 44 48 TABLE OF CONTENTS (Con't) Page Sm all W intered-O ver Cabbage A. B. XIII. M aterials and Methods R esu lts: 1. T em p eratu res During Growing Season 2 . C1PP T reatm ents 3 . 2 ,4 -D T reatm ents 4 . H ead-C ore Ratio 5 . Growth Phase Index 53 55 57 60 60 62 EXPERIMENT 4: The E ffect of T im e of Application of 2 , 4 -D and C1PP on Growth and Developm ent o f Large, Medium and Sm all Cold-Induced Cabbage A. B. XIV. M aterials and Methods R esu lts: 1. C1PP T reatm ents 2 . 2 , 4 -D T reatm ents 3 . H ead-C ore Ratio ■ 4 . Growth Phase Indices 5 . Seed Stalk Developm ent a . C1PP T reatm ents b . 2 , 4 -D T reatm ents 63 66 70 73 75 78 78 80 EXPERIMENTS: The E ffect o f T im e of Application of MH, T1BA and C1PP on Growth and Developm ent of Medium Size P artially Induced Plants A. B. XV. M aterials and Methods R esu lts 82 84 MORPHOLOGICAL STUDIES: 90 A. B. 90 94 M aterials and Methods R esu lts: 1. Seasonal Changes in the Term inal Growing Point of V egetative Plants 2 . L eaf Developm ent iv 94 97 T A B L E O F C O N T E N T S ( C on ft) Page 3. 4. 5. 6. 7. Som e Changes Which O c c u r in th e T e r m i n a l Growing P o in t of R e p r o ­ du ctiv e P la n ts L a t e r a l Shoot D ev elopm ent F lo w e r D evelopm ent E ffect of G ro w th -R eg u latin g S u b ­ s ta n c e s Upon T im e of Initiation a . L a r g e P la n t s b* M edium P la n ts c* S m a ll P la n t s S e a s o n a l Changes in th e T e r m in a l G ro w ­ ing P o in ts of P la n ts Kept V egetative by G ro w th -R eg u latin g S u b s ta n c e s 97 103 108 113 114 117 124 124 XVI. DISCUSSION 128 XVII* SUMMARY 142 XVIII. LITER A TU R E CITED 145 L IST O F F IG U R E S F ig u r e 1 2 3 4 5 6 7 8 9 10 11 12 Page A cabbage p lant t r e a t e d with 20 ppm 2 ,4 - D show ­ ing th ic k e n e d s te m and sp lit e p i d e r m i s . 30 A cabbage plan t t r e a t e d with 20 ppm 2 ,4 - D show ­ ing p r o li f e r a tio n of t i s s u e s , and an adventitious shoot a r is i n g f r o m th e a r e a affected . 31 C o m p a ra b le s iz e s of cabbage p lan ts at th e b e g in ­ ning of cold induction. 64 C o m p a ra tiv e s e a s o n a l grow th in height of la r g e , m e d iu m and s m a ll Golden A c re cabbage p lan ts s p r a y e d with 250 ppm of C1PP b e f o r e , during and a f te r cold induction. 68 C o m p a ra tiv e s e a s o n a l growth in height of l a r g e , m e d iu m and s m a ll Golden A c re cabbage p lan ts s p ra y e d w ith 15 ppm of 2 ,4 - D b e f o r e , during and a f te r cold induction. 72 Some effects of th e tim e of application of C1PP on th e p h a s e of growth in Golden A cre cabbage. 77 R ep ro d u ctiv e cabbage plan ts showing in c r e a s e d n u m b e r of seed sta lk s re s u ltin g f r o m C1PP trea tm en t. 77 P a r t i a l l y induced cabbage p la n ts following t r e a t ­ m ent with MH. 89 D ia g r a m m a tic r e p r e s e n ta tio n showing four d is tin c tiv e zones in the v eg etativ e growing point of cab b a g e. 93 T he growing point of a v eg etativ e cabbage plant h a r v e s te d F e b r u a r y 6. 93 T he growing point of a v eg etativ e cabbage plant h a r v e s te d M a rc h 27 • 96 T h e grow ing point of a v eg etativ e cabbage plant h a r v e s t e d A p ril 14. 96 vi L IST O F F IG U R E S (Con*t) F ig u r e Page 13 L e a f in itia tio n in a v e g e ta tiv e cabbage p la n t. 98 14 D evelo p m en t of le a f p r im o r d iu m in a v e g e t a ­ tiv e cabbage p la n t. 98 T h e growing point of a v eg etativ e cabbage plant showing a le a f p r im o r d iu m . 99 The growing point of a v eg etativ e cabbage plant showing le a f d ev elo p m en t. 99 The growing point of a cabbage plant h a r ­ v e s te d F e b r u a r y 6, which is p ro b ab ly r e ­ p r o d u c tiv e . 100 The growing point of a re p ro d u c tiv e cabbage plant h a r v e s te d F e b r u a r y 24. 100 The growing point of a r e p ro d u c tiv e cabbage plant h a r v e s te d M a rc h 10. 102 The growing point of a r e p ro d u c tiv e cabbage plant h a r v e s te d M a rc h 27 showing a p ro b ab le flo w er p r im o r d iu m . 102 The growing point of a r e p ro d u c tiv e cabbage plant h a r v e s te d M a rc h 27. 104 A developing l a t e r a l shoot p r im o r d iu m in cab b a g e. 104 A developing l a t e r a l shoot showing f i r s t p a ir of le a v e s in cab b ag e. 106 24 A developing l a t e r a l shoot in cabbage. 106 25 A re p r o d u c tiv e l a t e r a l shoot in cabbage. 107 26 F lo w e r in itia tio n in cabbage. 107 27 A developing flo w er in itia l in cabbage* 109 28 A developing flow er p r im o r d iu m in cab b ag e. 109 15 16 17 18 19 20 21 22 23 v ii LIST O F F IG U R E S (Con*t) F ig u r e 29 Page T h e d ev elo p m en t of a flow er showing sepal in itia ls in cab b a g e. 110 The develo pm en t of a flo w er showing sepal p r i m o r d i u m in cab b ag e. 110 The develop m en t of a flow er showing stam en p r i m o r d i u m in cab b ag e. 111 32 L ongitudinal sectio n of a cabbage flo w e r. 111 33 C r o s s s e c tio n of a cabbage flow er showing f lo r a l d i a g r a m . 112 P h o to g ra p h of a cabbage plant which was d e v e r n a liz e d by high t e m p e r a t u r e . 112 The growing point of a cabbage p lant (la rg e size) h a r v e s te d F e b r u a r y 24. 115 T he growing point of a cabbage plant (la rg e size) s p r a y e d with C1PP b e fo re cold-induction and h a r v e s te d F e b r u a r y 24. 115 The growing point of a cabbage p lant (la rg e size) s p ra y e d with C1PP during cold-induction and h a r v e s te d F e b r u a r y 24. 116 The growing point of a cabbage plant (la rg e size) s p ra y e d with C lP P a f te r cold-induction and h a r v e s te d F e b r u a r y 24. 116 The growing point of a cabbage plant (la rg e size) s p r a y e d with 2 ,4 - D b e fo re c o ld -in d u c ­ tio n and h a r v e s te d F e b r u a r y 24. 118 The growing point of a cabbage plant (la rg e size) s p r a y e d w ith 2 ,4 - D d u rin g co ld -in d u ction and h a r v e s te d F e b r u a r y 24. 118 The growing point of a cabbage plant (la rg e size) s p r a y e d with 2 ,4 - D a f te r c o ld -in d u c ­ tion and h a r v e s te d F e b r u a r y 24. 119 30 31 34 35 36 37 38 39 40 41 v iii LIST O F F IG U R E S (C on 't) Page The growing point of a cabbage p lan t (m ed iu m size) h a r v e s t e d F e b r u a r y 24. 119 The grow ing point of a cabbage plant (m edium size) s p r a y e d w ith C1PP b e fo re cold-induction and h a r v e s te d F e b r u a r y 24. 120 T he grow ing point of a cabbage p lant (m edium size) s p r a y e d with C1PP during cold-induction and h a r v e s te d F e b r u a r y 24. 120 T he growing point of a cabbage plant (m edium size) s p r a y e d w ith C1PP a f te r cold-induction and h a r v e s te d F e b r u a r y 24. 1 22 The growing point of a cabbage p lant (m edium size) s p r a y e d w ith 2 ,4 - D b e fo re cold-induction and h a r v e s te d F e b r u a r y 24. * 122 The growing point of a cabbage p lant (m edium size) s p ra y e d with 2 ,4 -D durin g cold-induction and h a r v e s te d F e b r u a r y 24. 123 The growing point of a cabbage plant (m edium size) s p r a y e d with 2 ,4 -D a f te r cold-induction and h a r v e s te d F e b r u a r y 24. 123 The growing point of a cabbage plant (m edium size) s p ra y e d with C1PP during cold-induction and h a r v e s te d J a n u a r y 20. 125 The growing point of a cabbage plant (m edium size) s p r a y e d with C1PP d u rin g cold-induction and h a r v e s t e d M a rc h 27. 125 The growing point of a cabbage plant (m edium size) s p ra y e d with C1PP durin g cold-induction and h a r v e s t e d A p ril 14. 126 ix L IST O F T A B L E S T a b le 1 2 3 4 5 6 7 8 9 10 11 Page Height of Cabbage P la n t s as Influenced by G row th R egulating S u b s ta n c e s ( v a r ie ty Golden A c re , n o n cold -in d u c e d ). 33 H eight of Cabbage P la n ts as Influenced by G rowth R egulating S u b s ta n c e s ( v a r ie ty Round Dutch, non cold - induced) • 35 Height of Cabbage P la n ts as Affected by Growth R egulating S u b stan ces ( v a r ie ty Golden A c re , co ld induced) • 37 Height of Cabbage P la n t s as Affected by Growth R egulating S u b s ta n c e s ( v a r ie ty Round Dutch, co ld induced) • 39 Head C h a r a c t e r i s t i c s and N u m b er of P ro b a b le S e e d e r s in Cabbage P la n t s as Influenced by G ro w th -R eg u latin g S u b stan ces (v a rie ty Golden A c r e , cold-induced)# 41 Head C h a r a c t e r i s t i c s and N u m b er of P r o b a b le S e e d e r s in Cabbage P la n ts as Influenced by G ro w th -R eg u latin g S u b stan ce s ( v a r ie ty Round D utch, c o ld -in d u c e d ). 43 The E ffect of G row th-R egulating S u b stan ces on th e Height of W in te re d -O v e r Golden A c re Cabbage. 49 The E ffect of G ro w th -R eg u latin g S u bstances on th e Height of W in te re d -O v e r Round Dutch Cabbage. 50 H e a d - C o r e Ratio and Growth P h a s e Index of W in te re d O ver Cabbage as Influenced by 2 ,4 - D , C1PP, TIB A and NA Applied B e fo re Cool W e a th e r. 52 A v erag e Weekly M axim um , M inim um and M ean T e m ­ p e r a t u r e s f r o m O cto b er 1, 1949 th ro u g h June 30, 1950, S tate C ollege, M is s is s ip p i. 56 The E ffect of T im e of A pplication of 250 ppm C1PP on th e A v erag e Height of L a r g e , M edium and S m all W in te r e d - O v e r Cabbage ( v a rie ty Golden A cre ). 58 x LEST OF TABLES (Con't) T a b le 12 13 14 15 16 17 18 19 Page T h e E ffect of T im e of A pplication of 15 ppm 2 ,4 - D on th e A v erag e Height of L a r g e , M edium and S m a ll W in te r e d - O v e r Cabbage ( v a r ie ty Golden A c re ). 59 T h e Influence of T im e of A pplication of 250 ppm C1PP and 15 pp m 2 ,4 - D on the H ead-C o r e Ratio and the G row th P h a s e Index in L a r g e , M edium and S m a ll W in te re d -O v e r Cabbage ( v a r ie ty Golden A cre). 61 T he Influence of T im e of A pplication of 250 ppm C1PP on th e A ccum ulative A verag e Height of L a r g e , M edium and S m all Cabbage at D ifferen t T im e s D uring the Growing S eason (v a rie ty Golden A c re , c o ld -in d u e e d ). 67 T h e Influence of T im e of A pplication of 15 ppm 2 .4 - D on the A ccum ulative A verage Height of L a r g e , M edium and S m all Cabbage P la n ts at D ifferent T i m e s D uring th e Growing S easo n (v a rie ty Golden A c r e , c o ld -in d u c e d ). 71 H e a d - C o r e Ratio and Growth P h a s e Index in L a r g e , M edium and S m a ll Cabbage P la n ts as Affected by T im e of A pplications of 250 ppm C1PP and 15 ppm 2 .4 - D ( v a r ie ty Golden A c re , c o ld -in d u ced ). 74 The E ffect of T im e of A pplication of 250 ppm C1PP and 15 ppm 2 ,4 - D on th e A verage N um ber of D ays f r o m C om pletion of Cold-Induction to th e A ppearan ce of Seed S talk s and th e N u m b er of P la n ts P ro d ucin g F lo w e rs. 79 The E ffect of 250 ppm of C e r ta in G row th-R egulating S u b s ta n c e s on the A verage Height of Cabbage P la n ts P a r t i a l l y Induced to F lo w e r by Cold T e m p e r a tu r e E x p o s u r e ( v a r ie ty Round D utch). 85 H e a d - C o r e Ratio and Growth P h a s e Index of Cabbage P la n t s P a r t i a l l y Induced to F lo w e r by Cold T e m p e r a ­ t u r e E x p o s u re as Influenced by T im e of Application of MH, TIB A, and C1PP (v a rie ty Round Dutch). 87 xi abstract S e p a r a t e o r in te r a c tin g effects of g ro w th -re g u la tin g s u b s ta n c e s , p la n t s iz e , and co ld -in d u c tio n on flow ering in Golden A cre and Round D utch cabbage w e r e stud ied in 1948 at M ichigan S tate College and in 1949, 1950 and 1951 at M is s is s ip p i S tate College* L a r g e ( s te m d i a m e t e r 9 m m .) m e d iu m (6 m m . ) , and s m a ll (4 m m .) p la n ts w e re s p r a y e d e i th e r b e f o r e , d u rin g o r a f te r cold -in d u ctio n of 38° F . fo r 42 d a y s . M edium s iz e p la n ts w e re s p ra y e d b e fo re cold w e a th e r . R e­ s p o n se s to c h e m ic a ls w e r e ev alu a ted by d e te rm in in g h is to lo g ic a lly th e t i m e of flo w er in itia tio n , seed s ta lk and flow er a p p e a r a n c e . The r a te of flo w er d ev elo p m en t, p lant heig h t, h e a d - c o r e r a t i o s , and an a r b i ­ t r a r i l y n u m b e re d growth p h a s e index w e r e also u se d in evaluating resp onses. Only c o ld -in d u ced p la n ts flo w e re d . m o r e r e a d i ly th a n m e d iu m o r s m a ll o n e s . L a r g e p lants flo w ered Applying 15 p p m 2 , 4 - d i - ch lo ro p h e n o x y acetic acid (2 ,4 -D ) to m e d iu m s iz e p lan ts d u rin g cold induction d elay ed flo w erin g , inhibited s e e d s ta lk developm ent, i n ­ c r e a s e d h e a d - c o r e r a t i o s , and p ro m o te d v eg etativ e grow th. V ege­ ta tiv e growth w as s tim u la te d , h e a d - c o r e r a tio s and head f i r m n e s s i n c r e a s e d in n o n co ld -in d u ced p la n ts s p ra y e d with 20 ppm 2 ,4 - D and 500 ppm alp h a, o rth o -ch lo ro p h en o x y p ro p io n ic acid (C1PP). S p ra y s of 250 p p m C1PP applied to m e d iu m s iz e Golden A cre p lan ts b e fo re and a f t e r co ld -in d u ctio n h a s te n e d flow ering t h r e e and two w eeks r e ­ s p e c tiv e ly , and i n c r e a s e d seed pod p ro d u c tio n . x ii P la n ts s p ra y e d during induction r e m a in e d vegetative* All l a r g e p la n ts flo w ered but th o s e s p r a y e d d u rin g induction w e r e two w eeks l a t e r th a n controls* E ssen­ ti a l l y a ll s m a ll p la n ts r e m a in e d vegetative* M edium s iz e Round D utch p lan ts s p ra y e d w ith 250 ppm m a le ic h y d r a z id e (MH) b e f o r e p a r t i a l induction p ro d u ced open h ead s in c o n ­ t r a s t to f i r m h ead s in c o n t r o l s . M ost p la n ts s p ra y e d w ith MH d u rin g p a r t i a l induction p ro d u c e d seed s ta lk s but no f lo w e r s . T e r m in a l buds w e r e k ille d and grow th inhibited g e n e r a lly by MH applied a f te r p a r t i a l in d u c tio n . In lim ite d t e s t s alpha naphthalene ac e tic acid (NA) s t i m u ­ la te d v e g e ta tiv e grow th, and 2, 3, 5 -triio d o b en zo ic acid (T1BA) c a u se d no a p p r e c ia b le e ffect. Shoot a p ic e s did not b eco m e d o m e -s h a p e d in the t r a n s i tio n f r o m v e g e ta tiv e to re p ro d u c tiv e d evelopm ent, but r e m a in e d m o r p h o ­ lo g ic a lly un chan g ed . The m o s t r e lia b le m o rp h o lo g ical changes a s ­ s o c ia te d with re p r o d u c tiv e grow th w e re fo rm a tio n of longitudinal row s of c e lls in th e r ib m e r i s t e m reg io n , grow th of l a t e r a l b u d s, and d w arfing of young l e a v e s . T h e s e changes o c c u r r e d about F e b r u a r y 24 in l a r g e and m e d iu m p la n ts . M o rphologically flow er in itiatio n o c c u r ­ r e d f i r s t in m e d iu m s iz e p la n ts s p ra y e d with 250 ppm C1PP b e fo re c old induction; next in th o s e sp ra y e d a fte r; th e n in th e co n tro l and did not o c c u r in p la n ts s p ra y e d durin g induction. With la r g e p la n ts in itia tio n o c c u r r e d f i r s t in p la n ts s p ra y e d b efo re; second, in p lan ts s p ra y e d a f te r ; t h i r d , in th e con tro l; and l a s t , in th o se sp ra y e d durin g in d u c ­ tio n . S m a ll p la n ts r e m a in e d v e g e ta tiv e . I^eaf and flo w er in itia ls a r o s e f r o m p e r ic lin a l cell d iv isio n in th e t h i r d and fo u rth c e ll l a y e r s of the flanking m e r i s t e m ju s t below th e shoot apices* F lo w e r s w e r e pro d u ced l a t e r a l l y as le a v e s and did not t e r m i n a t e th e s e e d s ta l k . The i r r e g u l a r a p p e a ra n c e of flo w er p a r t s w e r e s e p a ls , s t a m e n s , p i s t i l and l a s t l y p e ta ls * T h e findings in th is study w e r e d is c u s s e d on th e b a s i s of s y n ­ t h e s i s , le v e l, econom y, and d is tr ib u tio n of p h y to h o rm o n e s . A m ethod w as p r e s e n t e d fo r n u m e r i c a ll y evaluating re p ro d u c tiv e grow th. x iv SOME E F F E C T S OF CERTAIN GROWTH-REGULATING SUBSTANCES UPON PREM ATURE SEEDING IN CABBAGE INTRODUCTION Cabbage, B r a s s i c a o le r a c e a c a p i ta t a , L in n . , is a b ie n n ia l. G row th and. develo p m en t of th is crop m ay be divided in two p h a s e s ; (1) the v e g e ta tiv e p h a s e and (2) th e r e p ro d u c tiv e p h a s e . T he v eg e ta tiv e p h a s e , as in all p la n ts , c o n s is ts of the develop m ent of th e ro o t s y s te m , and the shoot and le a f s y s te m . The r e p r o ­ ductive p h ase c o n s is ts of th e developm ent of flow er buds, flo w e rs , f r u i t s and s e e d s . B e fo re th e s e r e p ro d u c tiv e s t r u c t u r e s develop in cabbage th e c e n t r a l axis elo n g a te s, and f o r m s a s t r u c t u r e r e f e r r e d to as a seed s ta lk . D evelopm ent of a seed s ta lk i s , in th is s e n s e , a p a r t of the re p ro d u c tiv e p h a s e . When cabbage a r e seed ed in the s p rin g the plants f o r m c o m ­ p a c t v eg e ta tiv e h ead s durin g la te s u m m e r o r e a r ly fa ll. If m a tu r e p la n ts a r e w in te r e d - o v e r in tact u n d er m ild w e a th e r conditions, the h ead s b u r s t when growth s t a r t s the following s p rin g . The te r m i n a l and s e v e r a l a x i lla r y buds elongate into seed stalk s producing flo w ers and seed th e following s u m m e r . Cabbage seeded la te in the s u m m e r m a y not f o r m head s b efo re cold w e a th e r . If th e s e p lan ts a r e allowed to w i n t e r - o v e r in cool w e a th e r th ey do not f o r m h e a d s , but shoot to seed when grow th s t a r t s in the s p rin g . This l a t t e r phenom enon of shooting to seed without f i r s t fo rm in g a he ad is known as p r e m a t u r e s e e d in g , com m o n ly r e f e r r e d to as " b o ltin g " . C on tro l of th e v e g e ta tiv e and r e p r o d u c tiv e p h a s e s of grow th is of g r e a t econom ic im p o r ta n c e to two ty p e s of f a r m e r s . One type is i n t e r e s t e d in p ro d u cin g cabbage fo r th e f r e s h m a r k e t o r fo r p r o c e s ­ sin g , and the o th e r is i n t e r e s t e d in seed p ro d u c tio n . With th e f o r m e r th e p la n ts m u s t be kept v e g e ta tiv e fo r m a r k e t a c c e p ta n c e . m a tio n of seed s ta lk s r e n d e r s th e cro p w o r t h l e s s . h a s the o p p o site o b je ctiv e in v iew . The f o r ­ The l a t t e r type I n t e r e s t s a r e d ir e c te d to w a rd s e e d s ta lk fo rm a tio n , seed p ro d u ctio n , and a high s ta te of r e p r o d u c ­ t i v e n e s s is d e s i r e d . In addition, p la nt b r e e d e r s a r e in t e r e s te d in seed s ta lk f o r ­ m a tio n . Only by inducing th e re p ro d u c tiv e r e s p o n s e can plant b r e e d e r s m ak e c r o s s e s to develop new v a r i e t i e s with d e s ir e d c h a r ­ a c t e r i s t i c s such as r e s i s t a n c e to bolting o r to d i s e a s e s . Often b r e e d e r s have d ifficu lty in p ro d u cin g flo w e rs fo r u se in c r o s s in g d e s i r e d v a r i e t i e s and s p e c i e s . T his is e s p e c ia lly t r u e w h e re cold s to r a g e f a c ilitie s a r e lack in g o r in a d eq u ate. T his n e c e s s i t a t e s r e s o r t i n g to n a t u r a lly cool w e a th e r of long d u ra tio n . As a r e s u l t flo w erin g o c c u r s d u rin g e a r l y s p rin g when the v eg etab le r e s e a r c h w o r k e r is involved in m any o th e r d u tie s . P r e s e n t m etho d s em ployed c o m m e r c ia lly fo r co n tro llin g th e v e g e ta tiv e and r e p r o d u c tiv e r e s p o n s e s in cabbage, as w ell as m a n y o th e r c r o p s , c e n te r aro u n d the knowledge of th e effects th at - 3 - c e r t a i n e n v iro n m e n ta l f a c t o r s have upon the crop# F i r s t th e cro p fo r m a r k e t is confined to th e s e a s o n of th e y e a r which is l e a s t conducive to b o ltin g , y et conducive to good growth in th a t g e o g ra p h ic a l lo c a lity . Second, th e a d ju s tm e n t of seeding d a te s so th e p la n ts w ill not b e e a s ily induced to bolt when a d v e r s e w e a th e r o c c u r s , and by supplying som e p r o te c tio n , such a s c o ld f r a m e s , fo r th e seed lin g s durin g a d v e r s e w e a th e r. T h i r d , th e u s e of v a r i e t i e s which have som e d e g r e e of r e ­ s is ta n c e to b o ltin g . N e ith e r of the above m ethods of co n tro l a r e e n t ir e ly s a t i s ­ factory* W e a th e r conditions a r e difficult to p r e d ic t and im p r a c ti c a l to c o n tro l u n d e r field c o n d itio n s . f r o m y e a r to y e a r . In m any lo c a litie s th e y flu ctu ate By choosing a seeding d ate which avoids t e m ­ p e r a t u r e s conducive to seed s ta lk fo rm a tio n one y e a r m a y not avoid t h e s e a d v e r s e conditions an o th e r y e a r . V a r ie t ie s which a r e " r e s i s ­ ta n t" to bolting m a y be in f e r i o r in o th e r r e s p e c t s . R e s is ta n c e to bolting also a c c e n tu a te s th e p r o b le m fo r the seed p r o d u c e r of i n ­ ducing th e v a r i e t y to p ro d u c e s e e d . In M is s is s i p p i cabbage h a s been an im p o rta n t v eg etab le cro p fo r about 60 y e a r s . The h a r v e s t p e rio d o c c u r s in th e e a r ly s p rin g when th e m a r k e t is good. In o r d e r to h a r v e s t cabbage at th is p e a k m a r k e t s e a s o n the p lan ts a r e s ta r t e d in the fall and a r e w in t e r e d - o v e r m a in ly in th e fie ld . F r e q u e n tly th e p la n ts a r e s u b ­ je c te d to p ro lo n g e d p e r io d s of cool w e a th e r . a r e e x te n siv e m an y of the p la n ts b o lt. If such conditions - 4 - Lioss due to bolting in c o m m e r c ia l p ro d u ctio n is difficult to e stim a te . M ost g r o w e r s pull up and th ro w away all " p o s s ib le - b o l t e r s " e a r l y in the s e a s o n . With such a p r a c t i c e an a c c u r a t e count of th e p la n ts which would a c tu a lly bolt is h a r d to o b ta in . v a r i e s f r o m y e a r to y e a r and among f a r m s . L o s s also It h a s b een noted th a t as high as s e v e n ty -fiv e p e r c e n t of th e p la n ts on som e f a r m s w ill bolt d u rin g c e r t a i n s e a s o n s , w hile in o th e rs bolting is n e g lig ib le . In m o s t in s ta n c e s bolting is e s tim a te d at five to fifteen p e r c e n t . Much w o rk h a s b een done and a v a s t r e p e r t o r y of in fo rm a tio n e x is ts on th e a ffects e n v iro n m e n ta l f a c to r s have upon the r e s p o n s e s of m any p l a n t s . E v en so, t h e r e is s till too little c o n c re te knowledge of th e m e c h a n is m (s ) involved in the plant when it is tr a n s f o r m e d f r o m th e v e g e ta tiv e to the r e p ro d u c tiv e p h a se of grow th. D urin g th e p a s t d ecad e effort h as b een d ir e c te d to w a rd th e effect of grow th s u b s ta n c e s upon growth r e s p o n s e s . If a su b sta n c e could be d is c o v e r e d th a t w ill inhibit seed s ta lk d evelopm ent, its ap p lic a tio n would be of g r e a t value to the f r e s h m a rk e t g r o w e r . C o n v e rs e ly , if a s u b sta n c e w e r e d is c o v e r e d th a t would induce o r accelerate: seed s ta lk f o rm a tio n it too would be v alu ab le to plant b r e e d e r s and seed p r o d u c e r s . With such a m a t e r i a l it m ight be th a t cabbage could be c h e m ic a lly induced to flow er d u rin g any s e a s o n of th e y e a r . T h e s e c o n s id e ra tio n s w e re in m ind when th is study was u n d e r ta k e n . - 5 - LITER A TU R E REVIEW T h e o r i e s r e g a r d in g th e c au se of flow ering in p la n ts have v a r i e d c o n s id e r a b ly among r e s e a r c h w o r k e r s d u rin g th e p a s t c e n tu r y . A c­ co rd in g to C aliach jan (9) Sachs advanced the th e o r y about I860 th a t v e g e ta tiv e and r e p r o d u c tiv e develo p m en t in p la n ts w as h o rm o n a l in n atu re . A lm o st s im u lta n e o u s ly K lebs in tro d u c ed the th e o r y th a t flo w erin g depended upon th e c a r b o h y d r a te - n itr o g e n r e la tio n s h ip . K le b s 1 th e o r y w as r e a d i ly accep ted and b e c a m e p o p u la r . T h is th e o ry w as l a t e r upheld and c a u se d to gain in p o p u la rity by K ra u s and K r a y b i l l 's (50) w o rk with t o m a to e s . The w o rk of G a r n e r and A lla rd (32) on p h o to p e rio d is m in r e a l i t y reo p en ed and s u p p o rted S ach fs t h e o r y . D u rin g th e e a r l y 1920*8 o th e r th e o r i e s w e r e ad v an c ed . D etjen (23) concluded th a t bolting was h e r e d i t a r y and behaved as a s im p le d o m in a te f a c t o r . re c e ssiv e fa c to r. Sutton (85) s u g g e sted bolting in cabbage w as a S im ila r co nclusions w e r e r e a c h e d by Van H eel (91) w hile w orking with b e e t s . A fter Knott (46) failed to induce th e r e p r o d u c tiv e p h a s e by chilling B r a s s i c a s e e d s fo r s e v e r a l w eeks during g e rm in a tio n , he s u g g e s te d th a t som e e n v iro n m e n ta l f a c to r which o c c u r r e d d u rin g the l a t e r s ta g e s of p lan t grow th m ight be re s p o n s ib le fo r inducing the r e p r o d u c tiv e p h a s e . P la n t r e s e a r c h durin g the p a s t few d e c a d e s has p ro v id ed m u c h in fo rm a tio n with r e s p e c t to the influence which v a r io u s e n v i­ r o n m e n ta l f a c t o r s have upon f lo r a l in itiatio n and d e v elo p m e n t. - 6 - Knowledge c o n ce rn in g th e in t e r n a l m e c h a n is m s involved is s till m e a g e r . M ille r (59) and B o sw ell (7) studied s e v e r a l e n v iro n m e n ta l f a c t o r s a s s o c ia te d with p r e c o c io u s seeding in cab b age. M ille r^ w o rk showed t e m p e r a t u r e was th e m o s t im p o rta n t single f a c to r a s ­ s o c ia te d with bolting in c a b b a g e . p l a n ts . Most of h is w o rk d ealt with m a tu r e He showed th a t 60 days of low t e m p e r a t u r e s (below 45° F . ) w e r e r e q u ir e d to induce th e re p ro d u c tiv e p h a s e . B o s w e ll's w o rk co n clu siv ely d e m o n s tr a te d th a t plant s iz e at th e ti m e o f cold induction w as a d e c is iv e f a c t o r . The l a r g e r the p la n ts when th e cold induction tr e a t m e n t was in itia ted the g r e a t e r th e n u m b e r of p la n ts which su b seq uen tly b o lted . P la n ts with a v e r a g e s te m d i a m e t e r s of 6 m m . o r l a r g e r r e a d ily bolted when su b jected to t e m p e r a t u r e s below 45° F . fo r two m o n th s. Two weeks of such low t e m p e r a t u r e changed the c h a r a c t e r of grow th of la r g e p la n ts . P la n ts w ith s te m d i a m e t e r s l e s s th a n 6 m m . at th e tim e of induction t r e a t ­ m e n t did not bolt as r e a d ily as l a r g e r p la n ts . B a s e d on th e findings of M ille r and B osw ell w ith r e s p e c t to t e m p e r a t u r e and s iz e of p la n ts , Knott (48) was able to c o n tro l bolting v e r y s a ti s f a c to r il y in C a lifo rn ia by m anipulating the planting d a t e s . Seven v a r i e t i e s w e r e t e s t e d . T h e r e w e re v a r ia tio n s among v a r i e t i e s , but in g e n e r a l, p lan ts f r o m th e seedin g s m ade during August, S e p te m ­ b e r and e a r l y O c to b e r p ro d u c e d head s in about fo u r m o n th s. P la n ts f r o m seed in g s m ade a f te r O cto b er 15 w e r e s m a ll when cool w e a th e r - 7 - o c c u r r e d and p ro d u c e d h e a d s th e following spring* C h ro b o cze k (12) w orking with b e e ts ; T hom p son and Knott (86) w ith le ttu c e ; Knott (47) with spinach; P la te n iu s (66) and T h om pson (87, 88) with c e l e r y a s s o c ia t e d bolting in m any v e g e ta b le c r o p s with a d v e r s e w e a th e r c o n d itio n s. A s y m p o siu m r e c e n tly p u b lish e d by M u rn e e k , Whyte et al (62) and a book by Whyte (101) contain c o m ­ p r e h e n s iv e re v ie w s of e x p e r im e n ts involving the effects of e n v ir o n ­ m e n ta l f a c t o r s upon d ev elo p m en tal growth in p la n ts . D u rin g th e p a s t few y e a r s ch e m ic a ls have been d is c o v e r e d to affect m any of the p h a s e s of d ev elo p m en tal grow th in p la n ts . C urrent atte n tio n is being d ir e c te d by m any s c ie n tis ts to the u s e of g ro w th re g u la tin g s u b sta n c e s as a p o s s ib le m e an s of co n tro llin g f lo r a l i n i t i ­ atio n and f lo r a l d ev elo p m en t in a v a r ie ty of p la n ts . A co m p lete r e ­ view of the l i t e r a t u r e on th is subject does not s e e m to be ju s tifie d s in c e s e v e r a l re v ie w s which a r e both c o m p re h e n s iv e and r a t h e r c o m ­ p le te have b e e n r e c e n t ly com piled (51, 62, 80, 97, 100, 107, 108). T h is rev ie w s h a ll, h o w ev e r, embody s e v e r a l p h a s e s of r e s e a r c h c o n ­ c e rn in g in fo rm a tio n e s p e c ia lly p e r tin e n t to th is study. Although th e t h e o r y th a t the co n tro l of plant r e s p o n s e s by c h e m ic a l s u b sta n c e s in which flow ering is but one c a s e was advanced a c e n tu r y ago (9) o r even e a r l i e r (100), it was Went (99) who f i r s t e x t r a c te d a su b sta n c e with g ro w th -re g u la tin g p r o p e r t i e s . H itch co ck and Z i m m e r m a n (38) w e r e among th e f i r s t to r e ­ p o r t th a t g ro w th -re g u la tin g s u b s ta n c e s have a p ro n ou n ced effect upon - 8 - flo w erin g in p l a n t s . They applied in d o le b u ty ric , in d o lep r op ionic, p h e n y la c tic and p h e n y lp ro p rio n ic a cid s to th e so il in w hich T u r k i s h to b a c c o p la n ts w e r e grow ing and o b s e rv e d th a t flow ering was h a s t e n ­ ed when e i th e r of th e s e s u b s ta n c e s w e r e applied about one month b e ­ f o r e th e n o r m a l flow erin g d a te . T h e s e findings, h o w ev er, w e r e not c o n firm e d in stu d ie s m ad e by M u rn e e k (61) with to m a to e s , to b a c c o , and s o y b e a n s . The m o s t s p e c ta c u la r exam ple of c h e m ic a lly co n tro llin g v e g e ­ ta tiv e and r e p r o d u c tiv e r e s p o n s e s in p la n ts is with th e p in e a p p le . C la r k and K e r n s (15) r e p o r te d th a t the p ineapple could be m ade to flo w er e a r l i e r th a n th e n o r m a l by applying low co n c e n tra tio n s of n a p h th a le n e a c e tic a c id . In s h a rp c o n t r a s t , flow ering could be d e ­ la y e d o r even s u p p r e s s e d by applying high c o n c e n tra tio n s of the sam e s u b s ta n c e . A so lu tio n containing 0.01 p e r c e n t of n a p h th a le n e a c e tic acid applied 30 days b e f o r e th e n o r m a l d ate fo r f lo r a l d iffe re n tia tio n d elay ed flo w erin g 90 d ay s in H aw aii. In F l o r i d a , C ooper and R e e se (18) induced p ineapple to flo w er d u rin g th e fall with eth y len e, a c e ty le n e , and n a p h th a le n e a c e tic a c id . N o rm a lly th e pin e ap p le does not flow er u n til J a n u a ry u n d e r F lo r id a c o n d itio n s. Indole compounds w e re not effectiv e. Cooper (17) i n ­ h ib ited flo w erin g in pin eap p le by applying l a r g e am ounts of n a p h th a le n e a c e tic a c id , and p ro m o te d flow ering with s m a ll a m o u n ts . When th is s u b sta n c e was applied during c e r t a in s e a s o n of th e y e a r p la n t r e s p o n s e w as d if f e r e n t. When applied in July flow ering was - 9 - in h ib ited and when applied in O cto b er flo w erin g was h a s te n e d . T he r e s u l t s o btained in F l o r i d a a r e not in co m p lete a g r e e m e n t with th o s e ob tain ed in H aw aii. A m o r e r e c e n t r e p o r t by Van O v erb eek (9 6 ) in d ic ate s th a t m any of th e " d ra w b a c k s " to the c h e m ic a l c o n tro l of flow ering in the p i n e ­ apple have been o v e r c o m e . P in e a p p le p la n ts begin to flow er a f te r being exposed to cool night t e m p e r a t u r e s in th e fall and continue to flo w er d u rin g th e w in te r m o n th s. Under n o r m a l c u ltu re m o s t v a r i ­ e tie s b eg in to flo w er and p ro d u ce f r u it at the age of eighteen m o n th s. S om e v a r i e t i e s , such as th e P u e r to R ic an C abezona, tak e as long as five y e a r s to flo w e r. Applying 0 .2 5 to 0 .5 0 m g . of n a p h th a le n e ­ a c e tic acid p e r plan t gives a lm o s t com p lete co n tro l of flow ering in th e Red S p an ish v a r i e t y in P u e r to R ic o . P la n ts re c e iv in g th is t r e a t ­ m en t b e a r t h e i r f r u it on a s le n d e r o r r e s t r i c t e d p ed u n cle. f a lls o v e r e a s ily . Such f r u it T h is h a z a r d can be o v e rc o m e by tr e a tin g c h e m ­ ic a lly induced p la n ts with B eta naphthoxyacetic acid a f te r fru it d e ­ v elo p m en t is u n d e rw a y . To co n tro l p r e m a t u r e flow ering la r g e am ounts of n a p h th a le n e a c e tic acid a r e n e c e s s a r y . T hus, acc o rd in g to Van O v erb e ek the c h e m ic a l c o n tro l of dev elo p m en tal grow th in th e pin eap p le is a r e a l i t y . This p r a c t i c e , u n d er c o m m e r c ia l u s a g e , en a b le s g r o w e r s to m ake a single h a r v e s t of an e n tir e p la n tin g . W h e r e a s , s e v e r a l h a r v e s t s a r e r e q u ir e d , due to i r r e g u l a r i t i e s of m a t u r i t y among p la n ts , w h ere flow ering is not chem icaU ycontrolled. With the p r o p e r u s e of n ap h th a le n e a c e tic acid pineapple plan ts can be - 10 - m ad e to flo w er d u rin g any m onth of the y e a r (96). co n tro llin g th e f l o r a l p r o c e s s in th is p lant (97). Auxin is involved in S m all am ounts of g r o w th - r e g u la tin g s u b s ta n c e s will p r o m o te flow ering (95). R e p o rts of w o rk with o th e r c ro p s have y ielded v a r ie d r e s u l t s . D o s ta l and H osek (25) w e r e th e f i r s t (1937) to show th a t flow ering could be inhibited by au x in . They s u c c e s s f u lly r e v e r t e d "flo w er r e a d y " C e r c a e a in t e r m e d ia to the v e g e ta tiv e habit with in d o leacetic a cid in lan o lin p a s t e . T he p o s s ib ility th a t high le v e ls of auxin m ay be h a r m f u l to f lo r a l in itia tio n was also su g g ested by G alston (30). C o n s id e ra b le evidence e x ists to su p p o rt th is p o s tu la tio n . Z im m er­ m a n and H itchcock (106) p ro m o te d flow ering in to m a to e s with t r i ­ iodobenzoic a c id . The n u m b e r of flo w ers p e r c lu s t e r w e re i n ­ c r e a s e d , and se ed lin g s w e r e induced to flow er b e fo re the n o r m a l flo w erin g tim e by sp ray in g the p lan ts with 25 to 500 m g / 1 of t r i iodobenzoic a c id . S im ila r r e s u l t s w e re obtained by W aa rd and Roodenburg (98) with a solution containing 200 m g . of triio d o b e n z o ic acid p e r l i t e r of w a t e r . G alsto n (31) found triio d o b e n z o ic acid to au g m en t the flow ering r e s p o n s e of Peking and Biloxi so y b ean s, to inhibit ap ical d o m in ance, in te rn o d a l elongation and th e a c tiv ity of in d o le a c e tic a c id . T h is c h e m ic a l failed to induce v eg etativ e s o y ­ b ean p la n ts to flo w er but g r e a tly i n c r e a s e d the flow ering r e s p o n s e to p h o to p e rio d ic a lly induced p la n ts . G alsto n su g g ested th a t t r i ­ iodobenzoic acid had " flo rig e n ic " p r o p e r t i e s which p ro m o te f lo w e r ­ ing. In th is connection he c o n s id e r s the two growth p h a s e s to oppose - 11 - ea c h o t h e r , F lo r ig e n te n d s to p r o m o te f lo r a l d iffe re n tia tio n and auxin (the g ro w th h o rm o n e) a n tag o n izes f lo rig e n by fa vo rin g v e g e ta tiv e g ro w th , P h o to p e r io d ic a lly induced X an th iu m , a s h o rt day p la n t, s p r a y e d with 500 p p m in d o le a c e tic acid and n a p h th a le n e a c e tic acid by T h u rlo w and B o n n er (90) f o r m e d no f lo r a l p r i m o r d i a . T h e s e a u th o rs conclude th a t auxin content d e c r e a s e s u n d e r s h o rt day conditions which p r o m o te d f l o r a l d e v e lo p m e n t. The application of a u x in -lik e c h e m ic a ls te n d to augm ent th e auxin content in th e p lant and nullify th e induction t r e a t m e n t . G re e n and F u l l e r (33) d elayed f lo r a l i n i t i ­ atio n in p etu n ia and soybean p la n ts , by applying in d o leacetic acid to th e r o o t s . F lo w e r developm ent was also delayed on p lan ts in itiatin g flo w e rs at the t i m e fo r t r e a t m e n t , Leopold and T h im an n (52) applied low (1 m g/1 o r le s s ) c o n ­ c e n tr a tio n s of in d o le a c e tic acid and alpha n aphthaleneacetic acid to W intex b a r l e y , a long day p la n t, and in c r e a s e d th e n u m b e r of f lo r a l p r i m o r d i a o v e r th a t of the control* In c o n t r a s t , flow ering was i n ­ h ib ite d when high c o n c e n tra tio n s (1 to 400 m g /1 ) of th e s e au x in -lik e c h e m ic a ls w e r e applied* T e o s in te , a s h o rt day p la n t, showed no su ch r e s p o n s e to th e c h e m ic a l t r e a t m e n t s . D o sag es of naphthalene - a c e tic a cid up to 400 m g /1 c a u se d inhibition of flow ering in e v e r y case. T h e s e a u th o rs c o n s id e re d th a t with b a r le y , as w ith th e p i n e ­ a p p le, auxin c o n c e n tra tio n e x e r te d an effect on flo w e rin g . It a p ­ p e a r e d th a t f lo r a l and v eg etativ e grow th w e re p ro m o te d by low and in h ib ited by high auxin concentration* Leopold and T him ann did not - 12 - c o n s id e r auxin to be n e c e s s a r i l y a n ta g o n is tic to the p ro d u c tio n of a flo ra l h o rm one. T h is concept is not in co m p lete a g r e e m e n t with that of G a ls to n (31), and Hamner (37)• B o n n er (4) and B o n n er and T hurlow (6) inhibited flow ering in p h o to -in d u c te d X anthium with n a p h th a le n e a c e tic acid and in d o leacetic a c id (au xin s), and p ro m o te d flow ering u n d er s h o rt p hotoperiod with 2, 4 - d ic h l o r a n is o le and 2, 3 , 5 -triio d o b e n z o ic acid (an ti-a u x in s o r auxin a n ta g o n is ts ) . The m o s t su ita b le c o n c e n tra tio n s w e r e 10 m g /1 of n a p h th a le n e a c e tic and 2, 4 - d ic h lo r a n is o le , and 30 m g/1 of t r i ­ iodobenzoic a c id . When triio d o b e n z o ic and n ap h th a le n e a c e tic acid s w e r e com bined into one t r e a t m e n t th e p la n ts showed no r e s p o n s e to e i th e r c h e m ic a l. Rice (70) applied v a r io u s g r o w th - r e g u la to r s to s e v e r a l crop p la n ts and concluded th at auxin and a u x in -lik e c h e m ic a ls d e la y flow ering in m o s t p la n ts . Leopold and G u e rn se y (55) have r e c e n t ly r e p o r te d the r o le of auxin in flow er in itiatio n of the A laska pea. The object of th e i r study was to develop a sim p le method fo r m e a s u r i n g the effects of added su b sta n c e s upon flo w erin g . Pea s eed lin g s g e r m in a te d in p a p e r tow els w e re soaked fo r four h o u rs in th e d e s i r e d s u b s ta n c e . The node at which flo w ers o c c u r r e d was u s e d as a c r i t e r i o n fo r m e a s u r in g plant r e s p o n s e . E n v iro n m e n ta l f a c t o r s w e re found to influence the node w h ere flo w ers f i r s t a p p e a re d , and a c o n tro l was ru n with each tr e a t m e n t u n d er s e v e r a l e n v ir o n ­ m e n ta l co n d itio n s. Under th e condition of th e i r co n tro l t r e a t m e n t th e f i r s t flo w e rs o c c u r r e d , in g e n e r a l, at th e seventh node. - 13 - N a p h th a le n e a c e tic acid c a u s e d a q u a n titativ e inhibition of flo w erin g at t e m p e r a t u r e s of 18 -2 0 ° C, H o w ev er, th e auxin t r e a t m e n t p ro m o te d flo w erin g in p la n ts held at 10° C* P la n t c o n stitu e n ts as s u c r o s e , a r g in in e and m a lic acid w e r e t e s t e d and found to inhibit flowering* Auxin applied in com bination w ith such s u b s ta n c e s o r u n d e r low t e m ­ p e r a t u r e conditions n u llified t h e i r inhibiting effect and p ro m o te d flow ering* F lo w e rin g was d elay ed in sto ck s by Johnson (43) and inhibited in m u s t a r d by s p ra y in g th e p la n ts t r i - w e e k l y with b eta -n a p h th o x y a c e tic acid* A lp h a-n ap h th o x y acetic acid was l e s s effective* H itchcock and Z i m m e r m a n (39) d elay ed flow ering in dandelions by sp ray in g th e p la n ts with 2, 4, 6 -tric h lo ro p h e n o x y a c e tic acid* W ittw e r, C o u lter and C aro lu s (102) c o n tro lle d bolting e x p e r i ­ m e n ta lly in c e l e r y by sp ra y in g th e p lan ts with o rth o -c h lo ro p h e n o x y p ro p io n ic acid* C la r k and W ittw er (14) obtained in te r e s tin g r e s u l t s w ith le ttu c e and c e l e r y p la n ts th a t w e r e s p ra y e d with g r o w th - r e g u ­ la tin g s u b s t a n c e s . S e v e r a l e x p e rim e n ts w e r e conducted with le ttu c e involving s e v e r a l c h e m ic a ls , c o n c e n tr a tio n s , and ti m e s of a p p l ic a ­ tion* E longation of th e seed s ta lk was ap p aren t f i r s t in p lan ts t r e a t e d with alpha o rth o -c h lo ro p h e n o x y p r op ionic acid in c o n c e n t r a ­ tio n s of 25 pp m and w ith 2 ,4 -d ic h lo ro p h e n o x y a c e tic acid in c o n c e n ­ t r a t i o n s of 10 ppm* T r e a tin g s m a ll p la n ts with 2 , 4 -d ic h lo ro p h e n o x y - a c e tic acid a p p e a re d to d w arf subsequent g ro w th . S eed s ta lk elongation w as h a s te n e d in p la n ts t r e a t e d at eight to tw elve w eeks of age, and - 14 - w hen r e p e a t e d a p p lic a tio n s w e r e m a d e . P r o g e n y of th e t r e a t e d p la n ts ex h ib ited a s tim u la tiv e r e s p o n s e s i m i l a r but of lo w e r m agnitude th an th e t r e a t e d p a r e n t . T h is s tim u la tiv e r e s p o n s e p e r s i s t e d even in the seco n d g e n e r a tio n . In each in s ta n c e , s tim u la tio n in seed stalk elo n g atio n was a c c o m p lis h e d e a r l y in th e s e a s o n , and G ran d Rapids th e v a r i e t y m o s t s u s c e p tib le to bolting showed th e g r e a t e s t r e s p o n s e . F r o m th is s e r i e s of e x p e r im e n ts ch e m ic a l c o n c e n tra tio n s and tim e of a p p lic a tio n w e r e found to have a p ro n ounced influence on the e f ­ fe c t g r o w th - r e g u la tin g s u b s ta n c e s have upon dev elo pm en tal g ro w th . T h e i r d ata f r o m th e c e l e r y e x p e r im e n ts su g g est th at f lo r a l p r i m o r d i a d if f e r e n tia te d at th e slo w est r a t e in 2 ,4 - D t r e a t e d p la n ts , and th a t a flu ctu atio n of phytohorm one content in the m e r i s t e m reg io n w as a s s o c ia te d with r a t e of d ev elo p m en tal grow th. P la n ts of C o rn ell 19, th e v a r i e t y th a t r e a d ily b o lted, and p la n ts re c e iv in g a cold t r e a t ­ m e n t w hich induced bolting exhibited h ig h e r c o n c e n tra tio n s of p h y to h o r m o n e s th a n n o n -b o ltin g p la n ts . A low le v e l of phytohorm ones e x is te d in th e m e r i s t e m s at o r ju s t p re c e d in g seed s ta lk d i f f e r e n t i a ­ tio n . Since Schoene and Hoffman (78) r e p o r te d m a le ic h y d ra z id e to have unique grow th re g u la tin g p r o p e r t i e s many p a p e r s on the r e ­ s p o n se s of p la n ts to th is c h e m ic a l have b een p u b lish e d . A very co m ­ p le te c o m p ilatio n of t h e s e in v e stig a tio n s h a s been m ade by Zukel (108, 109). Much of the w o rk with m a le ic h y d ra z id e h as been d ir e c t e d to w a rd te m p o r a r y o r p e r m a n e n t growth inhibition of g r a s s e s - 15 - and w e e d s . C o n s id e ra b le w o rk , h o w ev er, to w a rd the co n tro l of s p r o u t ­ ing in s t o r a g e , and the v e g e ta tiv e and r e p r o d u c tiv e r e s p o n s e s in a n u m ­ b e r of c ro p p la n ts h a s b een p u b lish e d . P r e h a r v e s t f o li a r s p r a y s of m a le ic h y d ra z id e have c o n tro lle d s to r a g e sp ro u tin g and sp o ilage of onions (103), c a r r o t s and onions (104), p o ta to e s (44), o n io n s, p o ta to e s , su g a r b e e ts and a n u m b e r of ro o t c ro p s (65, 105). T he in hibition of s te m grow th, bolting and flow ering by m a le ic h y d r a z id e h a s b e e n r e p o r t e d . E r ic k s o n and P r i c e (27) s p ra y e d co ld - induced s u g a r b e e t s , v a r ie ty U .S . 56 with 0 .1 and 0 .5 p e r c e n t m a le ic hydrazid e. ti o n s . S te m tip s in m any p lan ts w e re k illed by both c o n c e n t r a ­ The new ly developed le a v e s of p la n ts t r e a t e d with 0.1% m a le ic h y d r a z id e showed fo rm a tiv e e f f e c ts . Bolting p lan ts b e c a m e v e g e ta tiv e , and th e elongated s te m s p ro d u c e d t e r m i n a l r o s s e t t e s of le a v e s ; but r o o t grow th w as not r e t a r d e d by the t r e a t m e n t , N aylor and D avis (64) applied m a le ic h y d ra z id e in c o n c e n tra tio n s up to 0 .8 p e r c e n t to 11 p la n t s p e c ie s f r o m 5 f a m i l i e s . sim ila r. The r e s p o n s e s w e r e r e m a r k a b ly S e n s itiv ity to m a le ic h y d ra z id e a p p e a re d to d is s ip a te with plant age, and p la n ts t r e a t e d in th e seedling stage p ro d u ced no f lo w e r s . F lo w e rin g w as p r e v e n te d in tobacco and photo-induced X anthium by high c o n c e n tr a tio n s . X anthium t r e a t e d with low c o n c e n tra tio n s r e ­ q u ir e d a 30 m inute lo n g e r d a r k p e rio d fo r induction. N aylor (63) s p r a y e d the u p p e r and lo w er s id e s of T u r k i s h tobacco le a v e s with 0 .0 5 to 0 .8 p e r c e n t m a le ic h y d ra z id e when th e p la n ts w e r e beginning - 16 - to f lo w e r . P l a n t s s p r a y e d w ith c o n c e n tra tio n s g r e a t e r th a n 0 .2 p e r ­ cen t c e a s e d to flo w er; lo w e r c o n c e n tra tio n s s u p p r e s s e d t e r m i n a l grow th and d ev elo p m en t of i n f l o r e s c e n c e s . M aleic h y d ra z id e stopped flo w e r bud d ev elo p m en t on p h o to -in d u ced X anthium p la n ts . Inhibition of flo w erin g in V irg in ia b r ig h t le a f tobacco ( C if e r r i) and Havana seed to b a cco ( P e te r s o n ) s p r a y e d with m a le ic h y d ra z id e h as be en r e p o r t e d . N ay lo r (63) and M oore (60) obtained s trik in g effects with m a le ic h y d ra z id e on flo w er d ev elopm ent in c o r n . P la n ts s p ra y e d w ith c o n c e n tr a tio n s as low as 0 .0 2 5 p e r c e n t p ro d u ced s t e r i l e s t a m in a te i n f l o r e s e n c e s . M aleic h y d ra z id e h as delayed flow ering in m u s ta r d (20), r a d i s h (40), and p r e v e n te d bolting in onions (13) and s u p p r e s s e d flo w erin g in C roft E a s t e r l i lie s (83). C r a f ts , e t . a l . (21) studied the r e s p o n s e of 13 cro p s p e c ie s to m a le ic h y d r a z id e . Although d ifferen t s p e c ie s v a r ie d in b e h a v io r, th e age of th e plan t at tim e of t r e a t m e n t was a p r i m a r y f a c to r in d e te r m in in g plan t r e s p o n s e . th a n old plants* Young p la n ts w e re m o r e re s p o n s iv e In c o n tr a s t to p a p e r s cited above in which m a le ic h y d ra z id e inhibited r e p r o d u c tiv e developm ent C ra fts (19) found th a t b olting w as s tim u la te d in le ttu c e when 0 .1 p e r c e n t m a le ic h y d ra z id e w as applied to 2 0 -d ay old s e e d lin g s . B a r n a r d and W ard en (1) applied 0 .1 and 0 .5 p e r c e n t m a le ic h y d r a z id e to New York 12 le ttu c e seed lin g s one week old and o b ­ s e r v e d th a t t r e a t e d p la n ts had g r e a t e r bolting te n d a n c ie s th a n - 17 - c o n tr o ls. K o s a r and T h o m p s o n (49) p r o m o t e d b o ltin g in yo u n g l e t t u c e and p r e v e n t e d b o lt in g in o ld l e t t u c e w ith 0 . 1 - 1 , 0 p e r c e n t m a l e i c h y d r a z id e s p r a y s . In r e p o r tin g th e r e s u l t s of a s e r i e s of e la b o r a te e x p e r im e n ts involving t e m p e r a t u r e r a n g e s , n itro g e n le a v e ls and s e v e r a l c o n c e n ­ t r a t i o n s of m a le ic h y d r a z id e applied to c e l e r y p lan ts at d ifferen t s ta g e s of p la n t d e v e lo p m e n t, J a c k s o n (41) showed com p lete e x p e r i ­ m e n ta l c o n tro l of th e v eg e ta tiv e and re p r o d u c tiv e r e s p o n s e s in th is crop. E a c h f a c t o r stu d ied , m a le ic h y d ra z id e , n itro g e n and t e m p e r a ­ t u r e , s e p a r a t e ly o r in com bination influenced seed s ta lk d e v e lo p ­ m en t in C o rn e ll 19 c e l e r y . Low t e m p e r a t u r e , low ch em ical c o n ­ c e n tr a tio n s and a m e d iu m le v e l of n it r a te w e re found to be m o st conducive to s e e d s ta lk d ev elo p m en t. Young p lan ts s p ra y e d with 50 to 250 ppm m a le ic h y d ra z id e following a low te m p e r a t u r e t r e a t ­ m e n t of 40° F . and grow n at a n i t r a t e le v e l of 20 ppm flo w ered e a r l i e r and m o r e p r o fu s e ly th a n th e c o n t r o l s . High t e m p e r a t u r e , high c h e m ic a l c o n c e n tra tio n s and a low o r high n i t r a t e le v e l fa v o re d v e g e ta tiv e d e v elo p m en t. Ja c k s o n obtained ch em ical induction of th e r e p r o d u c tiv e p h a s e in young c e le r y p lan ts which w e re held at a t e m p e r a t u r e above 65° F . T im ing of the application and th e c o n c e n ­ t r a t i o n em ployed w e r e v e r y im p o r ta n t. P la n ts 10 to 14 weeks of age when t r e a t e d w ith 100 ppm of th e ch em ic al showed th e m o s t r e p r o ­ d u ctiv e r e s p o n s e . C o n cen tratio n s below 75 ppm w e re not effective e x cep t with c o ld -in d u ced p la n ts . - 18 - In c o m p a r is o n to stim u la tin g th e re p r o d u c tiv e r e s p o n s e with low c o n c e n tr a tio n s of m a le ic h y d ra z id e on young c e l e r y p la n ts , b o l t ­ ing w as s u p p r e s s e d with high c o n c e n tra tio n s applied d urin g the l a t e r s ta g e s of plan t d e v e lo p m e n t. All c o n c e n tra tio n s above 500 pp m a p ­ p lie d d u rin g th e l a t e r s ta g e s of growth inhibited seed s ta lk d e v e lo p ­ m e n t in c o ld -in d u ced and n o n -co ld induced p la n ts . A single a p ­ p lic a tio n of 1000 pp m of m a le ic h y d ra z id e to o ld e r p lan ts gave a l ­ m o s t c o m p le te c o n tro l of seed s ta lk d evelopm ent without any a p ­ p a r e n t in ju r y to th e m a r k e ta b le p o rtio n of th e p la n t. L a n g (51) h a s r e c e n t ly m ad e a r a t h e r com plete rev ie w of th e l i t e r a t u r e c o n ce rn in g th e physiology of flow ering and th e effects of g r o w th - r e g u la tin g s u b s ta n c e s on flo w erin g . M o rphological Studies S e v e r a l th e o r i e s have been em ployed in d e s c rib in g the o r g a n i ­ z a tio n of th e m e r i s t e m a t i c t i s s u e s in th e te r m i n a l growing point of p la n ts. E a m e s and M acD an iels (26) m ention two t h e o r i e s which a r e th e h is to g e n th e o r y and th e tu n ic a - c o r p u s th e o r y . In the f o r m e r th e o r y the t h r e e m a jo r re g io n s of the s te m a r e c o n s id e re d to a r i s e f r o m s e p a r a t e h is to g e n s . The o u te r re g io n is called th e d e r m a to g e n , th e c e n t r a l re g io n o r c o r e th e p le r o m e , and the re g io n b etw een th e d e r m a to g e n and the p le r o m e ,th e p e r ib l e m . The d e r m a to g e n f o r m s th e e p i d e r m i s , th e p e r ib l e m f o r m s the c o r te x and the p le r o m e f o r m s th e p ith . - 19 - The t u n i c a - c o r p u s th e o r y , f o r m u la te d by Schm idt (77) in 1924, h a s b e c o m e th e m o r e w idely acc e p te d th e o r y among a n a t o m i s t s . Two r e g io n s unlike in s t r u c t u r e develop in th e s te m apex due to d i f ­ f e r e n t r a t e s and p la n e s of c e ll d iv is io n . tu n ic a and th e in n e r r e g io n c o r p u s . T he o u te r r e g io n is c a lle d T he c e lls in the tu n ic a a r e s m a ll and divide p r i m a r i l y in an tic lin a l p la n e s . is p r i m a r i l y in th e tu n ic a . The grow th in a r e a C ells of th e c o r p u s , which account p r i n ­ cip ally fo r grow th in v o lu m e, divide in m any p la n e s . The p r in c ip a l d is a d v a n ta g e to th is m ethod of d e s c r ib in g th e a r c h i t e c t u r e of th e ap ex is th a t th e tu n ic a and co rp u s reg io n s a r e not c l e a r ly defined in m an y p l a n t s . F o r th is r e a s o n F o s t e r (28) w orking with C y c a s , Boke (3) w ith T r i c h o c e r e u s and O p u n tia, and Satina and B la k e s le e (76) w ith D a tu r a m odified th e tu n ic a - c o r p u s th e o r y . The shoot a p ic e s w e r e divided into t h r e e o r m o r e zones o r groups of i n i tia ls . F o s t e r h a s m ad e an adequate rev iew of the l i t e r a t u r e on the s t r u c ­ t u r e and grow th of th e shoot apex. G riffith (3 5) studying th e t e r m i n a l and l a t e r a l growing points of fo u r s p e c ie s of A r a u c a r ia divided th e m in four d e s c r ip tiv e z o n e s . The tu n ica was r e f e r r e d to as zone 1, co rp u s in itia ls as zone 2, p e r i ­ p h e r a l zone o r flanking m e r i s t e m as zone 3, and zone of rib m e r i s t e m as zone 4 . S houshan (79) working with L iliu m fav o red n u m b e rin g the cell l a y e r s and r e f e r r e d to th e m as f i r s t l a y e r , second l a y e r , and so on f r o m th e o u te r l a y e r in w a rd . T his m ethod e lim in a te s confusion of th e v a r io u s zon es as t h e r e is no d is tin c t lin e of d e m a r c a tio n in m any - 20 - p la n ts b etw ee n th e tu n ic a and co rp u s but r a t h e r a g ra d u a l t r a n s i t i o n f r o m one to th e o t h e r . V a rio u s m o r p h o lo g ic a l changes have b een r e p o r te d to o c c u r in m a n y p la n ts with o r even b e fo re the sw itch to re p ro d u c tiv e f r o m v e g e ta tiv e d e v e lo p m e n t. Changes such as a g r e a t e r s te m d ia m e te r a s s o c i a t e d w ith r e p r o d u c tiv e grow th w e r e o b s e r v e d in so u r c h e r r y (71), p lu m (72), and apple (73, 74). It was l a t e r found (82) with apple th a t th e m a r k e d s e c o n d a ry thickening of the fru it sp u r o c c u r a f te r flo w er bud in itia tio n . R o b e rts and O c ra (75) and S tr u c k m e y e r and R o b e r ts (84) ex am in ed s te m tip s at th e fo u rth node of s e v e r a l s p e c ie s of flo w erin g and n o n -flo w erin g p la n ts . They found c e r t a in a n a to m ic a l c h a r a c t e r i s t i c s a s s o c ia te d with flo w erin g . F lo w erin g p l a n ts , in c o n t r a s t to n o n -flo w erin g p la n ts , had le s s activ e c a m ­ b iu m , th ic k w alled c e lls in th e p e r ic y c le , p e r im e d u ll a r y zone and p h lo e m , and th in w alled c e lls in th e p a re n c h y m a to u s t i s s u e s . B o sw ell (7) stu d ie d the t e r m i n a l growing points of cabbage f r o m la te fall to e a r l y s p r in g . The f i r s t evidence of seed s ta lk p r i ­ m o r d i a d iffe re n t at ion w as n o ticed in sa m p le s co llected F e b r u a r y 4. P r i m o r d i a developed i r r e s p e c t i v e of plant s ize in all re p ro d u c tiv e p la n ts at about th e s a m e t i m e . He did not find a significant c o r r e l a ­ tio n b etw ee n plant s iz e and size of s te m apex, but noted an in c r e a s e in s iz e of th e a p ic e s of p o te n tia lly re p ro d u c tiv e p la n ts . D iffe re n c e s in s iz e of a p ic e s w e r e d e te c ta b le by the tim e growth c e a s e d in the fall o r even e a r l i e r . G r e a t e n la rg e m e n t of th e ap ices of p ote n tial - 21 - s e e d e r s o c c u r r e d d u rin g th e w in te r and e a r l y s p rin g , w h e r e a s th e a p ic e s of v e g e ta tiv e p la n ts r e m a in e d unchanged th ro u g h t h e i r d e ­ v e lo p m e n t. B o sw e ll r e p o r t e d th a t flo w e rs did not n e c e s s a r i l y a c ­ com pany an elongating axis and d e s tr u c tio n of th e t e r m i n a l bud did not p r e v e n t f l o r a l developm ent* He found th a t seed s ta lk p r i m o r d i a d ev elo p ed r a p id l y fo rm in g b r a n c h e s w ith m an y well developed flo w e rs w hich e m e r g e d f r o m th e head about A p ril 1* T h o m p so n (89) conducted a m ic r o s c o p ic a l study of cabbage f r o m f a ll seed in g until th e p la n ts r e a c h m atu rity* His study was d i r e c t e d m a in ly at th e develo p m en t of th e flower* F lo ra l p rim o rd ia w e r e f i r s t o b s e r v e d d u rin g la te F e b r u a r y and e a r l y M arch* The o r d e r of f l o r a l o rg a n a p p e a ra n c e w as found not to follow the u s u a l a c r o p e t a li c su c cessio n * T he se p a ls w e r e th e f i r s t o rg a n s to a p p e a r followed by th e s ta m e n s , c a r p e l s , and l a s t l y th e p etals* - 22 - MATERIALS AND METHODS T he e x p e r im e n ts h e r e i n d e s c r ib e d w e r e conducted in th e g r e e n ­ h o u s e at M ich ig an S tate C ollege d u rin g the 1948-49 s e a s o n , and in th e fie ld and g re e n h o u s e at M is s is s i p p i S tate College during the 1949-50 and 1951-52 s e a s o n s . Two cabbage v a r i e t i e s , Golden A c re and Round D utch which a r e w idely grown in c o m m e r c ia l p ro d u ctio n , w e r e s e ­ le c te d fo r th e stu d y . Golden A c re is s u sc e p tib le and Round D utch r e s i s t a n t to b o ltin g . Seeds fo r planting w e re obtained f r o m the F e r r y - M o r s e Seed Company and th e sa m e o r c o m p a ra b le stock s w e r e u s e d in a ll e x p e r i m e n t s . T he g ro w th - r e g u la tin g s u b sta n c e s u s e d w e r e 2 , 4 - d i c h l o r o p h en o x y acetic; alp h a, o rth o -ch lo ro p h en o x y p ro p io n ic ; 2 , 3 , 5 t r i ­ iodobenzoic; alpha n ap h th alen ea cetic; and m a le ic h y d ra z id e , h e r e ­ in a f t e r r e f e r r e d to as 2 , 4 - D , C1PP, T1BA, NA, and MH, r e s p e c ­ t i v e ly . The f i r s t fo u r c h e m ic a ls w e re u se d in the f o r m of t r u e a c i d s . The fifth, MH, was a w a te r soluble d ie th an o la m in e sa lt fo rm u la tio n p r e p a r e d by th e N augatuck C hem ical D iv isio n of United S ta te s R ubber Company, containing 30 p e r c e n t by weight of the activ e in g re d ie n t. F r e s h sto ck solutions of th e s e su b sta n c e s w e r e p r e p a r e d at th e beginning of each e x p e rim e n t by disso lvin g one g r a m of th e c r y s t a l s in 100 m i l l i l e t e r s ( m l .) o r 95 p e r c e n t ethyl alcohol, except fo r MH. It was found th at when MH, which is p r e p a r e d in solution f o r m by th e m a n u f a c tu r e r s , was diluted with alcohol to m ak e s t a n ­ d a r d sto ck so lu tio n s a white p r e c i p ita t e f o rm e d a f te r a few w eeks - 23 - in s t o r a g e . T h e r e f o r e , s ta n d a r d sto c k solu tio n s of MH w e r e p r e p a r e d in d i s t i l l e d w a t e r . The sto c k solutions w e r e diluted to th e d e s i r e d c o n c e n tr a tio n at th e t i m e of t r e a t m e n t with tap w a t e r . All c o n c e n ­ t r a t i o n s a r e e x p r e s s e d in p a r t s p e r m illio n (ppm) of th e grow th s u b ­ s ta n c e . The e x p e r im e n ta l d e s ig n in each in s ta n c e c o n s is te d of a r a n ­ d o m iz e d co m p lete b lo c k . W henever ap p lic a b le , the d ata contained in t h e s e in v e stig a tio n s w e r e analyzed fo r s t a t i s t i c a l s ig n ific a n c e . L e a s t d if f e r e n c e s r e q u i r e d fo r sig n ific an ce ( L . S . D . ) among t r e a t ­ m e n ts w e r e c a lc u la te d by a n a ly sis of v a r ia n c e (81). M a te r i a ls and m eth o ds which a r e sp ecific to an e x p e rim e n t a r e o utlined in d e ta il and p r e c e d e th e p r e s e n ta tio n of r e s u l t s fo r e a c h e x p e r i m e n t. - 24 - TERMINOLOGY The t e r m h e a d - c o r e r a tio is th e length of a cabbage head div id ed by its c o r e le n g th . T he t e r m grow th p h a s e index is a n u m e r i c a l v alu e applied to cab b ag e p la n ts denoting th e d e g r e e of v e g e ta tiv e n e s s a n d / o r re p ro d u c tiv e n e ss. A z e r o v alu e d en o tes co m p lete v e g e t a tiv e n e s s , w h e r e a s a v alu e of eight d en o tes co m p lete r e p r o d u c t iv e n e s s . The t e r m shoot as u s e d in th is p a p e r r e f e r s to the entity of th e t e r m i n a l and l a t e r a l growing points and the d iffe re n tia te d t i s ­ sues. The t e r m growing point a s u s e d in th is p a p e r r e f e r s to th e d iffe re n tia tin g t i s s u e s in its en tity in and about th e shoot t i p . T he t e r m apex as u se d in th is p a p e r r e f e r s only to the n o n - d if f e r e n tia te d t i s s u e lo c a te d in the e x tre m ity of the shoot tip , - 25 - EXPERIMENT 1, 1948-49 The f ir s t experim ent w as designed to obtain p relim in ary in for­ m ation . Inform ation w as d e sire d a s to whether certain growth substan ces influence s e e d sta lk developm ent in cabbage; which ch em ical had the g rea test in h ib itiv e and w hich ch em ical had the g rea test prom otive influence on growth; and the re la tiv e to lera n ce o f cabbage to variou s concentrations o f a number o f growth su b sta n ces. MATERIALS AND METHODS Seeds w ere planted February 24, 1948 in the horticultural g reen ­ h ou se at M ichigan State C o lle g e . The seed in g m ed ia u sed in the fla ts c o n siste d o f a m ixture of equal p a rts of fie ld so il and sand. Four hundred and fifty uniform seed lin g s of each variety w ere transplanted M arch 19 to 3 -in c h cla y p o ts and again on A pril 14 to 4 -in ch cla y p o t s . The purpose o f f ir s t transplanting to 3 -in c h p o ts w as to con serve greenhouse sp a c e. The potted p lan ts in each variety w ere arranged into seven teen groups o f tw en ty-five plants each in such a way that the plants in one group w ere a s n ea rly as p o ssib le the sam e s iz e a s the plants in each o f the other g ro u p s. The plants in each group w ere then numbered from one through tw e n ty -fiv e . Each of seventeen groups of plants for ea ch v a riety r e c e iv e d one o f the follow ing treatm en ts on A pril 18. - 26 - T re a tm e n t N u m b er C o n cen tratio n (PPM ) C h em ical 1 2 ,4 - D 5 2 2 ,4 - D 10 3 2 ,4 - D 15 4 2 ,4 - D 20 5 C1PP 50 6 C1PP 100 7 C1PP 250 8 C1PP 500 9 TIB A 50 10 TIB A 100 11 TIB A 250 12 TIB A 500 13 NA 100 14 NA 250 15 NA 500 16 NA 1000 17 W a ter C ontrol A fter th e sto ck solutions w ereyiiluted with tap w a te r 5 g r a m s I of D r e f t w e re added to each gallon of Solution. The D re ft was u s e d to im p ro v e th e s p re a d in g of the solution on the s u r f a c e s of the waxy l e a v e s . In o r d e r to p re v e n t co n tam in atio n among c h e m ic a ls , d if f e r e n t p ip e tte s and c o n ta in e r s w e r e u s e d fo r each c h e m ic a l. Solutions fo r - 27 - tr ea tm e n ts w ere p rep ared in deep enam eled pans and each plant w as dipped in the d e sir e d solution for ten se c o n d s . The pots in which the plants w ere grow ing w ere inverted and only the above-ground part of the plant w as e m e r se d into the solu tion . Plants at the tim e of treatm ent had four and five w ell developed le a v e s and the stem d iam eters averaged six m illim e te r s . The fir s t ten plants in each treatm ent w ere kept in the green h ou se w here the tem perature w as m aintained above 55 d eg rees Fahren­ h eit (°F ) by m eans of a th erm ostatically controlled steam heating s y s te m . T h ese p lan ts a re r e fe r r e d to a s noncold-induced p la n ts . T reatm ents w er e arranged in random ord er in each of two r e p lic a te s . The plants rem ain in g in each group w ere p laced in coldfram es for a cold-induction treatm en t w hich induces b o ltin g . They are r e ferred to as the cold-induced p la n ts . The treatm en ts w ere arranged in three random ized com plete b lock s of fiv e p lan ts e a c h . Outside night tem p eratu res exceed ed 4 5 ° F . after May 25, and the p lan ts w ere m oved May 28 to a cold storage room located in the horticultural building. The tem perature in the storage room w as con trolled by a therm ostat and held constant at 3 8 ° F . Light­ ing w a s inadequate for plant growth, th erefore, the plants w ere carted out o f the building and p la ced in the sunlight every other m orning at sev en o' clo ck and returned to the storage room that evening at five o 'c lo c k . A fter fifty-n in e days of induction treatm ent w here the night - 28 - t e m p e r a t u r e s w e r e below 45° F . th e s e p la n ts w e r e r e tu r n e d to the g r e e n h o u s e w h e r e th e t e m p e r a t u r e w as m a in ta in e d above 55° F . All p la n ts w e r e t r a n s p l a n te d to e ig h t-in c h po ts June 17 and 18. The pottin g m e d ia c o n s is te d of a m ix tu r e of tw o - th ir d s field soil and o n e -th ird m uck. In o r d e r to keep the p la n ts well supplied with n u ­ t r i e n t s 200 m l . of a n u tr ie n t solution was applied bim o n th ly to eac h p o t. T h e so lu tio n c o n s is te d of one ounce of 10-52-17 soluble f e r t i ­ l i z e r and two ounces of a m m o n iu m n i t r a t e d iss o lv e d in t h r e e and one h a lf g allons of w a t e r . Rotonone du st was u s e d to co n tro l cabbage w o r m s and s u lfu r to co n tro l soft r o t s . A e r ia l elongation of th e p lan ts was m e a s u r e d in c e n t im e te r s (cm) each w eek beginning A p ril 23 and ending N ovem ber 20. M or­ p h o lo g ical m o d ificatio n s p ro d u ced by the c h e m ic a ls w e re noted p e r io d i c a ll y . N otations of the g e n e ra l c h a r a c t e r of grow th, f i r m ­ n e s s of h e a d s and n u m b e r of p ro b a b le s e e d e r s w e r e also m a d e . In co llectin g th e d ata on the heading c h a r a c t e r i s t i c s a s c o r e of 1 was a s s ig n e d to f ir m ; 2 to lo o se; and 3 to open h e a d s . R e s u lts: N oncold-induced p la n ts P ro n o u n c e d m o d ificatio n s of the foliage w e r e a p p a re n t in c e r t a i n t r e a t m e n t s a few h o u r s a f te r th e y w e re ap p lied . T h e s e m o d i­ fic a tio n s w e r e c h a r a c t e r i z e d by tw istin g and cupping of th e m a tu r e le a v e s . In so m e in s ta n c e s the le a v e s w e r e tw is te d to the extent th a t th e ab a x ia l side of the le a f was in the ad ax ial p o s itio n . T w isting and - 29 - cupping o c c u r r e d among a ll p la n ts t r e a t e d with 2 ,4 - D in c o n c e n tra tio n s g r e a t e r th a n 5 p p m , and w ith 250 and 500 ppm of C1PP. f ic a tio n s These m o d i­ w e r e t e m p o r a r y b e c a u s e all p la n ts r e c o v e r e d w ithin 36 h o u rs a f te r t r e a t m e n t . F iv e d ays a f te r t r e a t m e n t t h e r e was g e n e r a l e p in a sty , widening and th ick en in g of th e p e tio le s and m a in s te m s and cupping of th e le a v e s of p la n ts t r e a t e d with 2 ,4 - D and C1PP. P la n t s t r e a t e d with 2 ,4 - D w e r e m o s t a ffe c te d and Golden A c re a p p e a re d to be m o r e affected th a n Round D u tch , The th ic k e n e d s te m s of p lan ts t r e a t e d with 2 ,4 - D eventually b e c a m e so e n la rg e d th a t th e e p id e r m is split fo rm in g a slit p a r a l l e l w ith th e lo ngitudinal axis of th e p la n t, F ig u r e 1, Within a few days t h e s e s lits b e c a m e fille d with p r o li f e r a te d t i s s u e of tu m o r o u s - l ik e g ro w th . F r o m t h e s e affected a r e a s a r o s e ad v en titio u s tu b u la r s t r u c ­ t u r e s which l a t e r developed into l a t e r a l shoots with m o rp h o lo g ical c h a r a c t e r i s t i c s id e n tic a l with th e m a in s te m , F ig u r e 2. Leaves d e ­ veloping on t h e s e ad v en titio u s shoots and on the m ain s te m s above the t u m o r s w e r e m uch d w arfed , cupped and th e p etio les w e r e elo n g ated . G row th in d i a m e t e r of th e m a in s te m was r e s t r i c t e d above the t u m o r s . T h is r e s t r i c t i o n w as e s p e c ia lly pronounced on p lan ts t r e a t e d with 20 p p m of 2 , 4 - D , L e s s p r o li f e r a tio n r e s u lt e d f r o m the C1PP c o n c e n tr a tio n s , but som e o c c u r r e d on p la n ts t r e a t e d with 250 and 500 ppm . No pro n o un ced m o d ific a tio n s w e r e o b s e r v e d in p la n ts t r e a t e d with T1BA o r NA, - 30 - F ig u r e 1. A cabbage plant t r e a t e d with 20 th ick en ed s te m and split e p i d e r m is . 9 ppm 2 ,4 - D showing - 31 - F ig u r e 2. A cabbage plant tr e a te d with 20 ppm 2 ,4 - D showing p r o lif e r a tio n of t i s s u e s , and an adventitious shoot a r is in g fro m the a r e a a f ­ fected . - 32 - P la n ts kept continuously in th e g re e n h o u s e m ad e r a p id grow th e a r l y in th e season* shown in T a b le 1* G row th in height of th e Golden A c re v a r i e t y is T h e s e d a ta show th e a v e ra g e height of th e p la n ts to th e t e r m i n a l bud f o r each t r e a t m e n t on th e d a te s s p e c ifie d . Although th e p la n ts w e r e m e a s u r e d each w eek only th e m e a s u r e m e n ts ta k e n at a p p r o x im a te ly 2 -m o n th in t e r v a ls a r e p r e s e n t e d . It can r e a d ily be se en th a t m o s t of th e grow th o c c u r r e d by Ju ly 24 and in m o st in s ta n c e s l i t t l e grow th w as m ad e betw een Ju ly 24 and S e p te m b e r 18. Ju ly and August t e m p e r a t u r e s w e r e v e r y high in th e g reen h o u se and m ay a c ­ count f o r th e r e d u c e d grow th r a t e durin g th is p e r io d . I n c r e a s in g th e 2 ,4 - D co n c e n tra tio n applied r e s u lt e d in a g r a d u a l i n c r e a s e in p lant height f r o m ti m e of tr e a t m e n t to May 21. The a v e r a g e height of th e p la n ts t r e a t e d with 5 ppm was not s t a t i s ­ t i c a l l y d iffe re n t f r o m th a t of th e control* P la n ts t r e a t e d with 10, 15, and 20 ppm w e r e sig n ifica n tly h ig h e r th an th e control* D if f e r e n c e s w e r e s m a ll on May 21 among th e p la n ts t r e a t e d w ith v a r io u s c o n c e n tra tio n s of C 1PP. Only p la n ts t r e a t e d with 100 ppm had an a v e r a g e height s ta t i s t i c a l l y g r e a t e r th a n th e c o n tro l p la n ts . T r e a t m e n t with TIB A did not a l t e r th e a v e ra g e heights of th e p l a n t s . A p p licatio n s of 100, 250 and 500 ppm NA slightly i n c r e a s e d the a v e r ­ age heig h t o v e r th a t of th e c o n tro l. By July 24 slig h t v a r ia tio n s ex isted in a v e ra g e plant h eig h ts among th e s e v e r a l t r e a t m e n t s but w e r e not g r e a t enough to be s t a t i s t i c a l l y s ig n if ic a n t. When th is e x p e rim e n t w as te r m in a t e d - 33 - T a b le 1 . H e ig h t of C a b b a g e P l a n t s a s I n flu e n c e d b y G r o w t h - R e g u la t in g S u b s t a n c e s ( V a r i e t y G o ld e n A c r e , N o n c o ld - I n d u c e d ) • G ro w th S u b s ta n c e s C h e m ic a l Sym bol PPM C o n tro l - 2 ,4 - D D ates of M e a s u re m e n t May 21 July 24 ( C e n tim e te rs ) S ep t. 18 7.1 26.0 3 2 .0 5 10 15 20 9 .6 11.8 13.8 14.3 2 3 .8 26.3 27 .8 28.7 2 7 .4 3 4 .2 3 0 .9 3 0 .8 C1PP 50 100 250 500 8 .4 10.6 9 .7 9 .2 22.3 28 .8 23.1 22 .8 2 8 .7 3 4 .5 2 6 .2 3 0 .4 T1BA 50 100 250 500 9 .8 9 .6 9 .5 7 .7 2 2 .7 26.5 23.9 22.0 2 7 .2 2 9 .4 29.1 3 0 .2 100 250 500 1000 10.2 10.9 10.1 9 .3 27.5 28.0 27.8 21.1 3 4 .2 37.3 33 .0 3 2 .5 3 .0 4.1 4 .5 N .S . N .S . NA L .S .D . @ .05 @ .01 m 34 — S e p te m b e r 18, no t r e a t m e n t d iffe re d s t a t i s t i c a l l y f r o m th e c o n tro l. A pplication of 2 ,4 - D to Round Dutch s tim u la te d a e r i a l grow th d u rin g th e f i r s t m onth following t r e a t m e n t and as can be s e e n in T ab le 2 a v e r a g e height in c r e a s e d w ith th e i n c r e a s e in c o n c e n tr a tio n s . In fact, th e a v e r a g e height of th e p la n ts re c e iv in g each of th e t h r e e h ig h e r c o n ­ c e n tr a tio n s w as a lm o s t tw ice th a t of the c o n tro l p la n ts on May 21 , P la n t s re c e iv in g e ith e r of th e C1PP c o n c e n tra tio n s had grown to g r e a t e r h eig h ts by May 21, th a n the c o n tro l. D uring th e f i r s t m o n th su b se q u en t to t r e a t m e n t growth r a t e s of th e s e p la n ts w e r e s i g ­ n ific a n tly d if f e r e n t f r o m th e co n tro l and f r o m p lan ts re c e iv in g 50, 100, and 250 pp m of TIB A. The above c o n c e n tra tio n s of TIB A a p ­ p e a r e d to s tim u la te grow th in the Round Dutch v a r ie ty . T h is r e ­ sp o n se w as in c o n t r a s t to no s tim u la tio n with th e Golden A c re v a r i e t y . Only th e 500 ppm c o n c e n tra tio n of NA sign ificantly stim u la te d growth r a t e in the Round Dutch v a r i e t y . D uring th e next 2 -m onth p e rio d , May 21 to July 24, t h e r e w as a t r e n d indicating th a t th e lo w e r the co n c e n tra tio n of 2 ,4 - D the g r e a t e r the r a t e of g ro w th . T a b le 2. T his fact is d e m o n s tr a te d by the data in T h e s e d ata show on July 24 no significant d iffe re n c e s in a v e r a g e height of co n tro l p la n ts and th o s e in e ith e r of th e 2 ,4 - D tre a tm e n ts. N e ith e r th e g ro w th -re g u la tin g su b stan ce n o r its c o n ­ c e n tr a tio n a l t e r e d the a v e ra g e height of p lan ts to the extent th a t th ey su fficie n tly d iffe re d f r o m the a v e r a g e height of the co n tro l p la n ts at the end of th e e x p e r im e n t. - 35 - T a b le 2 . H e ig h t o f C a b b a g e P l a n t s a s I n flu e n c e d b y G r o w t h - R e g u la t in g S u b s t a n c e s ( V a r i e t y Round D u tc h , N o n c o ld - I n d u c e d ) . G ro w th S u b s ta n c e s C h e m ic a l Sym bol D ates of M e a s u re m e n t PPM May 21 C o n trol - 4 .9 21.3 2 3 .5 2 ,4 - D 5 10 15 20 6 .6 9 .5 1 0 .4 11.1 19.9 2 2 .8 23.6 24.9 22.6 2 5 .4 2 7 .8 27 .7 C1PP 50 100 250 500 8 .8 7 .6 8 .3 9 .2 23.2 23.9 2 2 .8 23 .2 2 3 .5 27.7 3 0 .4 2 8 .8 TIB A 50 100 250 500 7 .4 6 .4 6 .4 6 .0 2 2 .2 21.3 2 1 .8 2 3 .4 26.1 27.6 25.9 2 5 .4 100 250 500 1000 5.9 5 .8 7 .3 5 .8 2 1 .2 21.8 21.6 22.5 23.9 26 • 6 28.7 29.5 1.3 1.8 N .S . N .S . N .S . N .S . NA L .S.D. @ .05 @ .01 July 24 (C e n tim e te rs ) Septo 18 -3 6 ~ B a s e d on th e d ata p r e s e n t e d above, with r e s p e c t to grow th of th e G olden A c re and Round D utch v a r i e t i e s as effected by growth r e g u la tin g s u b s ta n c e s , two m a in points stand ou t. (1) The ap p licatio n of 2 , 4 - D , C1PP and NA in d ilu te solutions te nd to s tim u la te a e r i a l e x te n s io n of the m a in axis of th e plant soon a f te r t r e a t m e n t . (2) S t i m ­ u la tio n of grow th is lo s t two to t h r e e m onths a f te r tr e a t m e n t and th e n o n - t r e a t e d p la n ts te n d to r e a c h a p p ro x im a te ly the s a m e u ltim a te height as th e t r e a t e d p la n ts . O th er points w o rth y of m ention a re : (1) In g e n e ra l the grow th r a t e in Golden A c re w as g r e a t e r th a n in Round D utch. (2) The r e ­ sp o n se to th e g r o w th -re g u la tin g s u b sta n c e s by th e two v a r i e t i e s w a s, in g e n e r a l , som ew hat s i m i l a r . C old-Induced P la n t s F o l i a r m o d ific a tio n s , s te m splittin g and t i s s u e p r o lif e r a tio n o c c u r r e d in about th e s a m e d e g r e e in cold-induced plan ts as d e ­ s c r i b e d fo r th e n on co ld -in d u ced p la n ts . Growth in height of th e Golden A c re p lan ts and the v alu es r e ­ q u ir e d fo r s ta t i s t i c a l sig n ifican ce a r e p r e s e n te d in T able 3. P la n ts t r e a t e d with 2 ,4 - D grew slig htly f a s t e r th a n the co n trol during the f i r s t m onth subsequent to t r e a t m e n t . to May 21, by 2 , 4 - D . Growth r a te was i n c r e a s e d , up T he d iffe re n c e in height betw een th e co n tro l p la n ts and th o s e t r e a t e d with 5 ppm was sig n ifican t. D iffe re n c e s b e ­ tw een th e c o n tro l p la n ts and th o s e t r e a t e d with 10, 15 and 20 ppm w e re - 37 - T a b le 3 . H e ig h t o f C a b b a g e P l a n t s a s A f fe c t e d b y G r o w t h - R e g u la t in g S u b s t a n c e s ( V a r i e t y G o ld en A c r e , C o ld - I n d u c e d ) • G row th S u b sta n c e s C h e m ic a l Symbol C o n tro l PPM D ates of Mea s u re m e n t May 21 July Sept. 24 25 (C entim et e r s) Nov. 20 5 .5 15.2 24.3 3 2 .5 5 10 15 20 6.3 7.1 7.1 7 .5 16.5 17.9 17.4 18.5 27.0 30.2 28.9 3 7 .5 4 1 .7 4 0 .2 3 6 .5 C1PP 50 100 250 500 5 .8 5 .5 5 .3 5.1 15.9 15.8 14.8 15.2 26.8 26.0 26 .5 25.9 3 6 .2 36.9 3 2 .5 3 2 .6 T1BA 50 100 250 500 5.9 5 .6 6 .0 5 .8 15,0 15.0 15.1 15.9 27.6 27.1 27.1 28.5 37.3 38.7 3 6 .5 41.1 100 250 500 1000 7 .0 6 .4 6 .0 4 .7 15.7 15.9 15.7 14.3 26.7 27.8 27.1 25.9 36.5 38.9 3 8 .5 34.7 N .S. N.S. 2 ,4 - D NA Li.S.D* - @.05 @.01 0.61 0.82 2 . 11 N.S. 29.2 - 38 - hig h ly significant* At no tim e d urin g th e growing s e a s o n w e r e any of th e C1PP t r e a t e d p la n ts sig n ifican tly h ig h e r th a n th e controls* P la n t s t r e a t e d with T1BA m a d e grow th a lm o s t id e n tic a l with th e c o n tro ls th ro u g h o u t th e exp erim en t* A stim u la tio n in growth w as noted e a r l y in th e s e a s o n f r o m 100 to 250 p p m NA, but did not p r e v a il l a t e r in th e season. The d ata on grow th in height of th e Round Dutch v a r ie ty a r e shown in T ab le 4. T h e r e w as little d iffe re n c e in u ltim a te height of p la n ts am ong th e v a r o u s t r e a t m e n t s (except w ith 2 ,4 - D at 20 p pm ). The lo w e r c o n c e n tra tio n s of 2 ,4 - D and C1PP did not i n c r e a s e the u l ­ t i m a t e height in th is v a r i e t y which was in c o n tra s t to the r e s p o n s e shown by th e Golden A c re v a r i e t y . H ow ever, all c o n c e n tra tio n s of 2 .4 - D s tim u la te d grow th in both v a r i e t i e s e a r l y in the s e a s o n as c o m ­ p a r e d to the c o n tro l. P la n t s t r e a t e d with 50 and 250 ppm C1PP w e re a ls o h ig h e r th a n the c o n tro ls on May 21. On July 24 th e d iffe re n c e s b e tw e e n th e h eig h ts of th e c o n tro l and p la n ts t r e a t e d with 15 and 20 pp m 2 ,4 - D and 250 ppm C1PP w e r e highly sig n ifican t. T h e r e was li t t l e d iffe re n c e in th e r a te of growth fo r th e 2 ,4 -D t r e a t e d p lan ts and th e c o n tro ls betw een May 21 and July 24. Only th o se p la n ts t r e a t e d with 15 and 20 ppm w e r e s ta t is tic a lly h ig h e r th a n the c o n ­ tro ls. By S e p te m b e r 25 th e d iffe re n c e s in heights among the 2 ,4 - D t r e a t e d and co n tro l p la n ts w e r e e s s e n tia lly the s a m e . D ata co n cern in g th e effect of v ary in g the c o n c e n tra tio n s of 2 . 4 - D , C1PF, T1BA and NA on th e heading c h a r a c t e r i s t i c s and th e - 39 - T a b le 4 . H e ig h t o f C a b b a g e P l a n t s a s A f f e c t e d b y G r o w t h - R e g u la t in g S u b s t a n c e s ( V a r i e t y Round D u tc h , C o ld - I n d u c e d ) • G ro w th S u b s ta n c e s C h em ical Sym bol C o n tro l PPM D ates of M e a s u re m e n t May 21 July S ept. 24 25 (C e n tim e te rs ) Nov. 20 - 4. 1 14.1 25.3 33.9 2 ,4 - D 5 10 15 20 5 .2 5 .0 5 .8 5.1 15.2 14.7 16.2 16.7 25.7 2 6.2 26.6 2 9 .4 3 2 .7 3 4 .0 33.3 39-3 C1PP 50 100 250 500 5 .6 4 .7 5.8 4 .6 15.7 14.7 16.1 14.5 2 6 .4 2 6 .4 2 5 .6 24.7 3 3 .4 3 2 .2 3 1 .7 30.3 TIB A 50 100 250 500 5 .0 3 .9 3 .7 4 .7 13.9 13.9 14.0 13.8 24.7 25.6 2 5 .4 24.7 31.1 3 2 .0 32 .5 31.1 100 250 500 1000 4 .2 4 .9 4 .9 3 .9 13.5 14.8 15.4 14.5 23.1 27.1 26.1 26.3 3 0 .8 3 3 .6 34.0 32.3 N .S . N .S . NA Li . S . D . @.05 @.01 0 .8 4 1.12 1.45 1.94 - 40 - n u m b e r of p ro b a b le s e e d e r s in Golden A c re a r e p r e s e n te d in T ab le 5. It a p p e a r s th a t in c r e a s in g th e co n c e n tra tio n of 2 ,4 - D above 10 ppm r e s u l t e d in a c o rre s p o n d in g i n c r e a s e in the n u m b e r of open h e a d s . of th e p la n ts t r e a t e d with 20 ppm of 2 ,4 - D p ro d u ced open h e a d s . All Leaves and s te m s of th e s e p la n ts had m any of th e c h a r a c t e r i s t i c s of r e p r o ­ d u ctiv e p la n ts , but none of th e m p ro d u ced a t r u e head n o r f lo w e r s . T h e h e a d s te n d ed to be l e s s f i r m with th e in c r e a s e in c o n ­ c e n t r a tio n of eac h c h e m ic a l except TIB A. nounced in p la n ts t r e a t e d with 2 , 4 - D . T his tr e n d was v e r y p r o ­ P la n ts t r e a t e d with 5 ppm r e ­ ceiv ed an a v e r a g e f i r m n e s s s c o r e of 1.70 and as the c o n ce n tratio n w as in c r e a s e d to 20 ppm th is s c o r e in c re a s e d to 3 .0 0 . A la rg e r n u m b e r of p ro b a b le s e e d e r s was noted in the p lan ts t r e a t e d with T1BA th a n with e ith e r of th e o th e r s u b sta n c e s o r the c o n tro l. T h e s e d a ta a r e m e r e l y indications and should not be r e li e d upon too s tr o n g ly . T he c h a r a c t e r of growth among th e v a r io u s t r e a t ­ m e n ts changed s e v e r a l t i m e s durin g the s e a s o n . E a r l y in the s e a s o n , th e s te m s and le a v e s of m any p la n ts w e r e ide n tica l with th o s e of r e ­ p ro d u c tiv e p la n ts . D u rin g Ju ly the t e m p e r a t u r e s in the g reen h o u se w e r e above 90° F . m o s t e v e r y d ay. A fter t h r e e weeks of th e s e high t e m p e r a t u r e s th e p la n ts r e v e r t e d fr o m th e r e p ro d u c tiv e to the v e g e ta tiv e p h a s e of g ro w th . Many p la n ts , when th ey w e re about 30 c m s t a l l beg an fo rm in g lo o se h e a d s . Such a r e s p o n s e su g g ests th a t th e high t e m p e r a t u r e s during July nullified th e cold -in d u ctio n t r e a t m e n t r e s u ltin g in a type of " d e v e r n a liz a tio n " . - 41 - T a b le 5 , H ea d C h a r a c t e r i s t i c s and N u m b e r o f P r o b a b le S e e d e r s in C a b b a g e P l a n t s a s I n flu e n c e d b y G r o w t h -R e g u la t in g S u b ­ s t a n c e s ( V a r i e t y G o ld e n A c r e , C o ld - I n d u c e d ) . G row th S u b s ta n c e s C h e m ic a l Symbol PPM C o n tro l 2 ,4 - D C1PP T1BA NA N um ber Heads F irm L>oose 5 6 5 10 15 20 5 10 15 9 50 100 250 500 5 1 50 100 250 500 100 250 500 1000 1 Open^ F irm n e ss P r o b a b le S co re^ S eeders 4 1.73 2 6 15 1.70 2.00 2.30 3.00 3 9 ? ? 9 14 12 12 1 1 2 3 1.73 2.07 1.86 2.13 2 6 5 6 13 15 14 14 2 1 1 2.00 2.00 2.07 2.07 10 5 11 9 2 2 1.93 2.00 2.13 2.13 3 6 7 2 14 15 13 13 1 P la n t s fo rm in g no t r u e heads w e re r e f e r r e d to as "open h e a d s " . ^ A s c o r e o f 1 w a s a s s i g n e d to f i r m , 2 to l o o s e and 3 to o p en h e a d s . T ab le 6 shows the effect of v ary in g th e c o n c e n tra tio n of 2 , 4 - D , C 1 P P > TlBA and NA on th e heading c h a r a c t e r i s t i c s and the n u m b e r of p r o b a b le s e e d e r s in co ld -in d u ced Round Dutch p la n ts . P la n ts t r e a t e d w ith 5 pp m 2 ,4 - D p ro d u c e d m o r e lo o se head s tha n the c o n tro ls . When th e c o n c e n tra tio n w as in c r e a s e d to 10 ppm the n u m b e r of p la n ts p r o ­ ducing f i r m h ead s w as a lm o s t th e sa m e as in th e c o n tro l. In c re a s in g 2 , 4 - D c o n c e n tra tio n s to 15 and 20 ppm r e s u lte d in s till g r e a t e r i n ­ c r e a s e s in th e n u m b e rs of f i r m head s p ro du ced and a co rresp o n d in g d e c r e a s e in th e f i r m n e s s s c o r e . Although m o re f i r m heads w e re p ro d u c e d by p la n ts t r e a t e d with 15 and 20 ppm of 2 ,4 - D , th e s e head s w e r e only o n e -h a lf as l a r g e as th o s e p ro d u ced by the co n tro l p la n ts . T h is r e s p o n s e of Round Dutch to 2 ,4 - D a p p e a rs to be opposite to th a t o btained with Golden A c r e . An i n c r e a s e in the f i r m n e s s s c o r e was a s s o c ia te d with an i n ­ c r e a s e in c o n c e n tra tio n of C1PP, but no co n siste n t re la tio n sh ip b e ­ tw een th e n u m b e r of p ro b a b le s e e d e r s and the c o n ce n tratio n of C1PP w as found. As the c o n c e n tra tio n of TlBA was in c r e a s e d , an in c r e a s e in th e n u m b e r of f i r m head s and consequently a d e c r e a s e in the f i r m ­ n e s s s c o r e was n o ted . A d e c r e a s e in n u m b er of f ir m heads was a s ­ so c ia te d with an i n c r e a s e in c o n ce n tratio n of NA in co n ce n tratio n s up to 500 p p m . H ow ever, as the co n ce n tratio n of NA w as in c r e a s e d to 1000 pp m t h e r e w as an in c r e a s e in n u m b e r of f ir m head s p ro d u ced . - 43 - T a b le 6 . H ea d C h a r a c t e r i s t i c s and N u m b e r of P r o b a b l e S e e d e r s in Cabbage P la n t s as Influenced by G ro w th -R eg u latin g S u b ­ s ta n c e s (V a r ie ty Round Dutch, C old-Indueed). G row th S u b s ta n c e s C h e m ic a l Sym bol PPM C o ntro l 2 ,4 - D C1PP 5 1.30 2 6 0 2 0 0 1 . 86 1 0 0 0 1 0 0 0 1.46 1.53 1.80 1.86 0 0 0 0 1.73 1.70 1.26 1.13 6 0 0 0 0 0 1 . 00 0 1 2 0 9 12 20 14 1 50 9 7 3 4 8 12 2 13 4 5 11 10 250 500 11 4 13 2 100 14 1 250 500 10 5 5 10 1000 12 3 100 NA 0 15 50 P r o b a b le Seeders 5 9 4 3 100 F irm n e ss S c o re ^ 10 10 250 500 TlBA N u m b er Heads F irm L o o se Open-*- 1.53 1 . 20 1.07 1.33 1.70 1.20 1 3 0 2 3 2 1 P la n t s fo rm in g no t r u e heads w e r e r e f e r r e d to as "open h e a d s ” . ^ A s c o r e o f 1 w a s a s s i g n e d to f i r m , 2 to l o o s e and 3 to o p en h e a d s . « 44 - EXPERIM ENT 2 - 1950 In fo rm a tio n obtained f r o m e x p e rim e n t 1 indicated th at grow th s u b s ta n c e s affected th e c h a r a c t e r of growth of cabbage grown in th e greenhouse* E x p e r im e n t 2 w as d esig ned to obtain in fo rm atio n on th e effect grow th s u b sta n c e s m ight have upon th e c h a r a c t e r of growth of cabbage grow n in th e field* In fo rm atio n was d e s ir e d as to w h eth er o r not c e r t a i n grow th s u b sta n c e s would induce o r inhibit bolting and th e r e la tiv e t o l e r a n c e of cabbage to v a rio u s co n ce n tratio n s of th e s e s u b s ta n c e s u n d e r field co n d itio n s. MATERIALS AND METHODS Seeds of th e Golden A cre and Round Dutch v a r i e t i e s w e re p la n te d O cto b er 10, 1949 in flats in the h o r tic u ltu r a l g reen h o u se at M is s i s s i p p i S tate C o lleg e. The seedlin g s w e r e tra n s p la n te d to cold- f r a m e s N o v em b er 1 in tr e a t m e n t groups s e p a r a te d by eig h teen -in c h alleys* The p u r p o s e s of th e alley s w e r e to fa c ilita te the application of th e grow th s u b s ta n c e s and to allow sp ace fo r placing w a t e r - r e p e l la n t canvas sh ield s to e lim in ate d rift of s p r a y fr o m one plot to another* P la n ts at the tim e of t r e a tm e n t had four and five well developed le a v e s and s te m d i a m e t e r s which av erag e d about six m illim e te r s * The grow th s u b s ta n c e s and co n c e n tra tio n s w e re as d e s c r ib e d in e x p e rim e n t 1. A pplication was m ade J a n u a r y 12, 1950 with a "S u re Shot” c o m ­ p r e s s e d a i r s p r a y e r at 75 to 100 pounds p r e s s u r e . Individual s p r a y e r s w e r e u sed fo r each growth su b stan ce and the lo w er co n ce n ­ t r a t i o n s applied f i r s t . Im m e d ia te ly a f te r use the s p r a y e r s w ere - 45 -> w a sh e d by allowing tap w a te r to ru n th ro u g h th e m for at le a s t two h o u r s . T h e s p r a y was applied to the e n tir e p lant with s p ecia l e m p h a sis p la ced on getting good co v e ra g e of th e growing point. The s p r a y was applied to th e r u n - o f f . F o r t y p la n ts of each t r e a t m e n t w e re tr a n s p la n te d to the field F e b r u a r y 20, te n in each of four ran d o m ized com plete b lo c k s. P la n ts w e r e sp aced fifteen inches a p a r t in row s fo rty inches wide in p lo ts lo c a te d on soil c la s s ifie d as Kaufm an clay lo a m . The soil was s u p ­ p lie d w ith 1000 pounds p e r a c r e of 6 - 8 - 4 f e r t i l i z e r applied in th e d r i l l b e f o r e tr a n s p la n tin g . An additional 200 pounds of n it r a te of soda to th e a c r e w as applied as a s i d e - d r e s s i n g a f te r the d an g er of cold w e a th e r had p a s t . T e m p e r a t u r e s w e re a s c e r t a in e d by re c o rd in g th e rm o g r a p h s f r o m th e date of seeding until th e com pletion of the e x p e r im e n t. t u r a l p r a c t i c e s w e r e kept u n ifo rm for each t r e a t m e n t . C u l­ W ater fo r i r r i g a t i o n w as applied as needed with a P e r f - O - R a in s p r in k le r s y s te m a tta c h e d to a d o m e s tic w a te r lin e . Weeds w e r e co n tro lled with t r a c ­ t o r d raw n c u ltiv a to rs and by hand hoeing. Insects w e r e c o n tro lled by dusting with D . D . T . and sp ray in g with nicotine s u lfa te . P la n t h eig hts w e re r e c o r d e d s e m i-m o n th ly in c e n tim e te r s beginning M a rc h 9 and ending May 11, but only the bim onthly m e a su re m e n ts a re p resen te d . The p lan ts w e re h a r v e s te d June 2 and June 6 and d is s e c t e d fo r study with r e s p e c t to th e ir d e g r e e of d ev e lo p m e n t. The length of the c e n tr a l c o re and the to ta l length of - 46 - th e head w as m e a s u r e d in all of th e p la n ts f r o m each t r e a t m e n t . The po in t on th e s te m w h e re the lo w er w r a p p e r le a f was a tta c h e d was u s e d as a b a s a l point fo r th e s e m e a s u r e m e n t s . F r o m th is b a s a l point to th e ap ex of th e t e r m i n a l bud co n stitu te d th e c e n tr a l c o r e . The d is ta n c e f r o m th is s a m e point to th e u p p e r m o s t point of the folded le a v e s which f o r m th e h ead co n s titu te d the to ta l length of th e h ead . The m e a s u r e ­ m e n t fo r th e to ta l length of each head was then divided by its c o r r e s ­ ponding c e n t r a l c o r e le n g th . The r e s u ltin g quotient is h e r e a f t e r r e f e r ­ r e d to in th e th e s i s as th e h e a d - c o r e r a t i o . The h e a d - c o r e r a tio of each p la n t in a t r e a t m e n t was su m m ed and the a v e ra g e d e te r m in e d . Ratio v a lu e s ra n g e d f r o m one fo r re p ro d u c tiv e to ap p ro x im a te ly two fo r v e g e ta tiv e p la n ts with v e r y f i r m h e a d s . The h e a d - c o r e ra tio was found to be a v e r y effective method for sco rin g the p la n ts with r e f e r ­ ence to the d e g r e e of re p ro d u c tiv e a n d /o r v eg etativ e developm ent ex ce p t in p la n ts th a t had p r o g r e s s e d to m o re advanced d e g r e e s of r e p r o d u c t iv e n e s s . T h e r e a r e s e v e r a l d e g r e e s of r e p ro d u c tiv e n e s s in cabbage. P la n t s p ro d u ce f i r m , lo o se o r no t r u e h e a d s . They m ay p ro d u ce a p o o rly developed seed s ta lk with no flow ers o r well developed seed s ta lk s with m any flo w ers and f r u i t s . F o r th is re a s o n it was found e a r l y in th e s e stu d ie s th a t the h e a d - c o r e ra tio did not p r e s e n t the e n t ir e p i c t u r e . F o r in s ta n c e , c e r ta in p la n ts that had a h e a d - c o r e r a tio of one p ro d u ced a seed stalk and no flo w ers o r f r u i t s . W h erea s o th e r s with a ra tio of one p ro d u ced s e v e r a l seed s ta lk s and m any - 47 - flo w e rs and f r u i t s . T h e r e f o r e , a method was developed in which the v a r i e d d e g r e e s of v e g e ta tiv e n e s s and r e p r o d u c tiv e n e s s w e r e p la c e d on a n u m e r i c a l b a s i s . The n u m e r i c a l values ran ged fr o m z e r o to eight a s follows: 0 -V eg etativ e p la n ts producing v e r y f i r m h e a d s . 1 -V eg etativ e p lan ts producing f i r m h e a d s . 2 -V eg etativ e p la n ts producing slightly loose h e a d s . 3 -V eg etativ e p la n ts p roducing loose h e a d s . 4 -V e g e ta tiv e -R e p ro d u c tiv e plan ts producing v e r y lo ose h e a d s , and l a t e r a l buds th a t w e re slightly e n la rg e d . 5 -R e p ro d u c tiv e p lan ts with only a p a r ti a l head, seed s ta lk e m e rg e d but p o o rly developed and producing no f lo w e r s . 6 -R ep ro d u ctiv e p la n ts with no developed head, seed stalk p r e s e n t and no flo w ers o r fru it p r e s e n t . 7 -R ep ro d u ctiv e p lan ts with a w ell developed seed s ta lk and few to s e v e r a l flo w ers and f r u it p r e s e n t. 8 -R ep ro d u ctiv e p lan ts with s e v e r a l well developed seed sta lk s and m any flo w ers and f r u it p r e s e n t . The above outlined n u m e ric a l d e s c r ip tio n was u se d in th is and su b seq u en t e x p e r im e n ts r e p o r te d in th is p a p e r . Such a method of ev alu atio n is h e r e a f t e r r e f e r r e d to as the "grow th p h ase in dex". ■ 48 * RESULTS T h e d ata on the effect of v a ry in g the co n c e n tra tio n of the four g ro w th - r e g u la tin g s u b s ta n c e s upon the a v e r a g e heights of w in te re d o v e r G olden A c re and Round D utch p la n ts a r e shown in T a b le s 7 and 8 , re sp e c tiv e ly . R e sp o n se of the Golden A cre V a r ie ty T he a v e r a g e h eig h ts of 2 ,4 - D t r e a t e d Golden A cre p lan ts w e r e not s t a t i s t i c a l l y d iffe re n t f r o m th e c o n tro ls on M arch 9« P la n ts s p ra y e d w ith 100 and 500 pp m C1PP, 50 and 250 ppm of TlBA, and 500 and 1000 p p m of NA w e r e s h o r t e r th a n the c o n tr o ls . On A pril 13, p la n ts s p ra y e d with 15 pp m of 2 ,4 - D w e r e h ig h e r, and th o s e sp ra y e d with 50 ppm of TlBA w e r e s h o r t e r th a n the p lan ts of the c o n tro l. The a v e ra g e height of th e p la n ts in the o th e r tr e a t m e n t s did not v a r y fro m the c o n tro l. T h e r e w e r e no sig n ificant d iffe re n c e s on May 11 in th e a v e ra g e h eig h ts of th e p la n ts among the v a r io u s t r e a t m e n t s . R e sp o n se of th e Round Dutch V a rie ty The d ata with r e s p e c t to Round Dutch (Table 8 ) w e r e som ew hat s i m i l a r to th a t of Golden A c r e . T h e r e w e re d iffe re n c e s in heights among c e r t a i n t r e a t m e n t s M arch 9 . P la n ts sp ra y e d with 10 ppm of 2 , 4 - D and 100 ppm of NA w e r e h ig h e r th a n the c o n tro ls . The effects of grow th r a t e r e s u ltin g f r o m th e s e g ro w th -re g u la tin g s u b sta n c e s o c ­ c u r r e d e a r l y in the s e a s o n . This in d icate s th at any i n c r e a s e o r d e ­ c r e a s e in growth due to th e s e s u b sta n c e s o c c u r s soon a f te r t r e a tm e n t - 49 - T a b l e 7• T h e E f f e c t o f G r o w t h - R e g u la t in g S u b s t a n c e s on th e H e ig h t o f W i n t e r e d - O v e r G o ld en A c r e Cabbage* G row th S u b s ta n c e s C h em ical Symbol C o ntro l 2 , 4-D PPM - 11 5 .4 4 .0 5 .4 5 .0 8.2 15.2 7.9 16.6 8.8 8.0 14.8 13.6 250 500 3 .6 3 .0 3 .6 3.3 6 .4 5 .7 5 .8 5 .8 15.0 14.0 13.0 14.2 50 2.8 5 .4 6 .5 5 .7 - 12.6 5 50 100 100 3 .7 250 500 2.6 100 3 .8 3 .4 3 .0 3 .3 6 .4 1.2 1.8 250 500 1000 L .S . D . May 16.2 15 NA A pril 13 ( C e n tim e te rs ) 7.1 20 TlBA M a rc h 9 4 .5 10 C1PP B a te s of M e a s u re m e n t @ .05 @ .01 - 13.8 1 4 .4 - 6.6 15.7 15.0 7 .4 16.2 6.2 15.9 1.7 2.3 N .S . N .S . - 50 - T a b le 8 . T h e E f f e c t of G r o w t h -R e g u la t in g S u b s t a n c e s on th e H eig h t o f W i n t e r e d - O v e r Round D u tch C a b b a g e . G row th S u b s ta n c e s C h em ical Symbol M arch PPM C o n tro l - 2 ,4 - D 5 10 15 20 C1PP 50 100 250 500 TlBA 50 100 250 500 NA 100 250 500 1000 L .S .D . D ates of M e a s u re m e n t @.05 @. 0 1 9 A pril 13 ( C en tim eters) May 11 2 .7 4. 4 12.7 4 .0 4 .8 3 .8 4 .4 7 .0 7 .2 13.8 13.7 13.0 14.8 6.0 8 .4 3 .8 3 .6 3 .3 3 .2 6.6 3 .3 3.1 3 .0 3 .8 5 .4 5 .4 4 .5 4 .8 3 .2 3 .4 3.3 6.8 2.0 2 .7 5 .8 6.6 5.1 6.6 13.0 13.0 14.4 11.7 13.6 13.8 13.8 14.2 6.2 6.0 13.7 13.6 13.3 13.1 N .S . N .S . 5 .2 if o th e r e n v iro n m e n ta l f a c t o r s a r e fa v o ra b le fo r grow th. L a t e r in the s e a s o n t h e s e s u b s ta n c e s lik e ly had been u tiliz ed o r t r a n s f o r m e d into in a c tiv e m a t e r i a l s . H e a d - C o r e Ratio and G row th P h a s e Index A pplication of 2 , 4 - D , C1PP o r TlBA had no effect on th e h e a d c o r e r a t i o s of e ith e r v a r ie ty , T ab le 9« H ow ever, ap plicatio n of NA at a c o n c e n tra tio n of 100 ppm to Golden A cre in c r e a s e d th is r a ti o . The grow th p h a s e index w as red u ced in Golden A cre by 5 ppm of 2 ,4 - D , 100 p p m of NA, and 50 and 500 ppm of C1PP. The d iffe re n c e s in the in d ices of the c o n tro l p la n ts and th o s e s p ra y e d with 500 pp m of C1PP and 100 pp m NA w e r e highly s ig n ifican t. The in d ices for the Round Dutch v a r ie ty re s u ltin g fr o m the v a r io u s t r e a t m e n t s w e re not s ta t i s t i c a l l y d iffe re n t. Due to the la c k of su fficien tly cool o r cold t e m p e r a t u r e s un d er the p re v a ilin g field conditions none of th e p la n ts p ro d u ced seed s ta l k s . The h e a d - c o r e r a ti o and the grow th p h a se index w e r e , un d er th e s e conditions, not g r e a t ly changed by the g ro w th -re g u la tin g s u b s ta n c e s . - 52 - T a b le 9 . H e a d - C o r e R atio and Growth. P h a s e Index of W in te re d -O v e r Cabbage as Influenced by 2 ,4 - D , C1PP, TlBA, and NA A p­ p lie d B e fo re Cool Weather* G row th S u b s ta n c e s C h e m ic a l Sym bol PPM C on tro l 2 ,4 - D 1.41 2.85 2 .3 8 1.46 1.45 1.45 1.45 1.38 1.43 1.41 1.49 2.3 8 2.76 2.82 2 .8 0 2.49 2 .3 2 2 .3 4 1.46 1.49 1.52 1.52 1.52 1.48 1.51 1.42 2.41 2.02 2.68 2 .2 8 2.76 2.31 2.41 250 500 1.51 1.53 1.45 - 1.42 1.45 1.40 1 *46 2.53 2.56 2.6 7 100 1.68 250 500 1.40 1.51 1.33 1.43 1.41 1.43 1.47 2.31 3 .0 4 2 .6 4 2.7 6 0 .1 4 0.1 9 N .S . 0.4 0 0.53 N .S . 1.48 1 .4 4 2.57 2.3 3 5 15 20 50 100 250 500 TlBA 50 100 NA 1000 L • S • D. G rowth P h a s e Index G .A .* R . D .* 1*40 10 C1PP H e a d -C o re Ratio G .A .* R .D . * @ .05 @ .01 G e n e r a l V a r ie ty M eans 2.68 - * G . A* - Golden A cre v a r ie ty ; R.D* - Round Dutch variety* 1.88 2.40 2.33 2.60 2.2 7 2.22 2.31 2.31 2.30 - 53 - EX PERIM ENT 3, 1950 P l a n t s iz e when cold t e m p e r a t u r e s o c c u r is known to be a fa c to r w hich d e t e r m i n e s th e extent of bolting in cab b ag e. m o r e r e a d i ly th a n s m a ll p la n ts . L a r g e p la n ts bolt The p u r p o s e of e x p e rim e n t 3 w as to d e t e r m in e the effects of grow th s u b s ta n c e s on seed s ta lk developm ent when ap p lied to " l a r g e " , " m e d iu m " , and " s m a ll" p lan ts at d iffe re n t t i m e s d u rin g a p e r io d of cool w e a th e r . MATERIALS AND METHODS To obtain " l a r g e " , " m e d iu m " , and " s m a ll" p la n ts , seed s of Golden A c re w e r e p lan ted in the g reen h o u se S ep te m b er 17, O cto b er 10 and N o v em b er 2, 1949. T h e se seedlings w e re tr a n s p la n te d to cold- f r a m e s O cto b er 2, N ovem ber 2 and N ovem ber 23 for the f i r s t , second, and t h i r d seeding d a t e s , r e s p e c tiv e ly . The p la n ts of each s iz e ( la r g e , m ed iu m and sm all) r e c e iv e d one of th e following tr e a t m e n t s : T re a tm e n t N u m b er C hem ical C on cen tratio n ' (ppm) T im e of Application 1 C ontrol - 2 C1PP 250 D e c . 20,1949 3 C1PP 250 J a n . 23,1950 4 C1PP 250 F e b . 1 6 ,1950 5 2 ,4 - D 15 D ec. 20, 1949 6 2 ,4 - D 15 J a n . 23,1950 7 2 ,4 - D 15 F e b . 16,1950 - 54 - T h is m a d e a to t a l of tw en ty -o n e t r e a t m e n t s . The d i a m e t e r s of th e p la n t s te m s ju s t below th e f i r s t t r u e le a f on D e c e m b e r 2 0 , 1949 a v ­ e r a g e d 9 m m . fo r th e l a r g e , 6 m m . fo r th e m ed iu m and 4 m m . for th e sm all p la n ts . T h e d a te s fo r t i m e of ap p licatio n of th e grow th s u b ­ s ta n c e s w e r e s e le c te d b e c a u s e th e y w e r e expected to m o r e n e a r l y co v er th e p e r io d of a n tic ip a te d cool w e a th e r th a n any o th e r two m onth p e r io d d u rin g th e y e a r . It was d e s i r e d th a t th e f i r s t s p r a y d ate be b e f o r e o r at th e beginning of cool w e a th e r; th e second date during cool w e a th e r; and th e t h i r d , a f te r o r n e a r th e end of cool w e a th e r . T em p eratu res in th e c o ld fra m e w e r e m a in ta in e d above 50° F* until D e c e m b e r 24 by m e a n s of a t h e r m o s t a t i c a l l y c o n tro lle d soil heating cable and by c o v e rin g th e c o ld fr a m e s with g la ss s a s h when t e m p e r a t u r e s lo w er th a n 50° F . w e r e p r e d i c t e d . On D e c e m b e r 24, th e cab les w e r e d i s ­ conn ected and th e s a s h re m o v e d f r o m th e c o ld fr a m e . th e w in te r of 1949-50 w as m i ld . U nfortunately Low t e m p e r a t u r e s fo r p e r io d s of t i m e s u fficie n tly long to induce th e re p ro d u c tiv e p h a se did not p r e v a i l at M i s s i s s i p p i S tate C o lleg e. The p re v a ilin g te m p e r a t u r e s w ill be d is c u s s e d in th e sectio n on r e s u l t s . L a r g e p la n ts m a d e ra p id growth and b eca m e so crow ded in th e c o ld fr a m e th a t th e y w e re tr a n s p la n te d to th e field D e c e m b e r 7, 1949. T h e r e f o r e , th e l a r g e p la n ts w e r e s p ra y e d a fte r th e y w e r e tr a n s p l a n te d to th e f ie ld . M edium and s m a ll s iz e p la n ts w e re sp ra y e d while in th e c o ld fra m e and t r a n s p l a n te d to th e field F e b r u a r y 17, 1950. In a ll i n ­ s ta n c e s p r e c a u t io n a r y m e a s u r e s to g u ard ag ain st contam inating - 55 - a d ja c e n t p lo ts w e r e em ployed as d e s c r ib e d in e x p e rim e n t 2 . T he tw en ty -o n e t r e a t m e n t s c o n sistin g of th r e e plant s iz e s and s e v e n c h e m ic a l s p r a y s w e r e a r r a n g e d in five ra n d o m iz e d blocks in the f ie ld . E ach of th e f i r s t fo u r blocks co n s is te d of te n p la n ts of each t r e a t ­ m en t f r o m which d ata co n cern in g growth and developm ent w e re c o lle c te d . T he fifth b lo ck c o n s is te d of 50 p la n ts r e s e r v e d fo r making m o r p h o ­ lo g ic a l stu d ie s of the t e r m i n a l shoot. T h is e x p e rim e n t w as lo c a te d ad jacen t to and re c e iv e d the s a m e c u l tu r a l t r e a t m e n t as d e s c r ib e d in ex p erim en t 2. D ata w e re c o llected as d e s c r ib e d in e x p e rim e n t 2 . H eights of th e p la n ts w e re m e a s u r e d at a p p ro x im a te ly 2 week in t e r v a ls f r o m F e b r u a r y 27 to May 11 in c lu siv ely , but only bim onthly m e a su re m e n ts a re p re se n te d . h a r v e s t e d A p ril 20. L a r g e p lan ts r e a c h m a tu r ity and w e re T h e r e f o r e , th ey w e r e not included at the l a t e r m e a s u r i n g d a te s (T ab les 11 and 12). M edium and s m a ll p lan ts w e re h a r v e s t e d May 12 and June 6 , r e s p e c tiv e ly . C onsequently, the m ed iu m and s m a ll p la n ts w e r e m e a s u r e d tw ice a f te r th e l a r g e p la n ts w e re h a r ­ v e ste d . RESULTS T e m p e r a t u r e D uring Growing S eason Weekly a v e r a g e m a x im u m and a v e ra g e m in im u m t e m p e r a t u r e s and w eek ly m e a n s durin g th e p e r io d D e c e m b e r 24, 1949 to June 30, 1950 a r e p r e s e n t e d in T ab le 10. A v erag e m a x im u m t e m p e r a t u r e s fo r - 56 - T a b le 10. A v erag e Weekly M axim um , M inim um and Mean T e m p e r a t u r e s f r o m O cto b er 1 , 1949, th ro u g h June 30, 1950, S tate C ollege, Mis sis s ip p i. Weekly A verage T e m p e r a tu r e * M inim um Mean 60.2 35.6 49.0 45.1 44.6 52.6 47.3 4 9 .6 4 0 .4 35.1 36.6 36.6 4 0 .7 4 2 .6 46.7 44.1 4 3 .5 4 2 .8 56.0 5 7 .5 58.0 54.0 56.5 60.0 6 5 .4 68.9 71.7 67.6 7 1 .4 6 7 .8 8 1 .0 78.1 8 5 .4 82.9 85.6 8 6 .4 81.0 89.6 90.0 9 0 .7 61.6 67.1 60.0 65.7 79.0 6 5 .4 66.7 7 1 .4 67.6 * Seven daily t e m p e r a t u r e v alu es included in each a v e r a g e . 62.2 56.3 59.6 51 .7 4 9 .6 4 9 .2 48.3 53.0 5 5 .8 59-2 5 5 .8 5 7 .4 55.3 6 8 .5 6 9 .8 7 6 .2 7 1 .4 7 5 .6 82 .7 7 3 .2 78.2 o 67.1 62.9 6 8 .4 71.9 65.3 69-7 63.0 64.0 61.9 • D e c . 24 - D e c . 30 D e c . 31 - J a n . 6 J a n . 7 - J a n . 13 J a n . 14 - J a n . 20 J a n . 21 - J a n . 27 J a n . 28 - F e b . 3 F e b . 4 - F e b . 10 F e b . 11 - F e b . 17 F e b . 18 - F e b . 24 F e b . 25 - M a r . 3 M a r . 4 - M a r . 10 M a r . 11 - M a r . 17 M a r . 18 - M a r . 24 M a r . 25 - M a r . 31 A p r . 1 - A p r. 7 A p r. 8 - A p r. 14 A p r. 15 - A pr. 21 A p r. 22 - A p r. 28 A p r. 29 - May 5 May 6 - May 12 May 13 - May 19 May 20 - May 26 May 27 - June 2 June 3 - June 9 June 10 - June 16 June 17 - June 23 June 24 - June 30 M axim um 00 D ate 79.2 - 57 - each w eek w e r e n e v e r below 6 0 ° F •, and w e r e well above 6 0 ° m o s t of th e p e r i o d . A v erag e m in im u m t e m p e r a t u r e s w e r e 45° F . and below for only 12 w e e k s . Weekly m e a n te m p e r a t u r e s w e re not as low as 45° F . fo r a sin g le w eek d urin g th e p e r io d . The lo w est weekly m ean t e m p e r ­ a t u r e r e a c h e d w as 4 8 . 3 ° F . and o c c u r r e d during the sev en day p e r io d M a rc h 4 - M a rc h 10, 1950. T e m p e r a tu r e s w e re not low enough fo r su fficie n t tim e to induce r e p ro d u c tiv e developm ent, h o w ev er, th ey w e re su fficien t to influence th e c h a r a c t e r of head developm ent in th e l a r g e p la n ts. T h e s e in flu en ces w ill be d is c u s s e d l a t e r . D ata on s e a s o n a l growth in height of l a r g e , m ed iu m and s m a ll s iz e s of p la n ts s p r a y e d with C1PP and 2 ,4 - D a r e p r e s e n te d to T a b les 11 and 12, r e s p e c t iv e ly . L a r g e p lan ts w e re much h ig h e r A p ril 10, th e fin al m e a s u r e m e n t d ate for th e la r g e p la n ts , th an th e m e d iu m o r s m a ll p la n ts on each d ate of m e a s u r e m e n t. The final height re a c h e d b y th e m e d iu m siz e group was about the sa m e as the la r g e group, h o w ­ ever. C1PP T r e a tm e n t s The effect of the tim e of applying C1PP on the r a t e of growth o r u ltim a te height of l a r g e p la n ts was not s ta tis tic a lly s ig n ifican t. H o w ev er, p la n ts s p ra y e d during cool w e a th e r w e re th e h ig h e st of the group and th o s e s p ra y e d a f te r cool w e a th e r w e re the lo w e s t. T here w e r e sig n ifica n t d if f e r e n c e s in the r a t e of growth due to the tim e of applying C1PP in th e p la n ts of th e m ed iu m g ro u p . P la n ts sp ra y e d - 58 - T a b le 11. T he E ffect of T im e of A pplication of 250 P P M C1PP On th e A v erag e Height of L a r g e , M edium and S m all W in tered O v er Cabbage (V a rie ty Golden A c r e ) . D ates of M e a s u re m e n ts S ize of P la n t s L arge T im e of A pplication* C ontrol B efo re D uring A fter G e n e r a l S ize M eans M edium C ontrol B e fo re D uring A fter G e n e r a l S ize M eans S m a ll C ontrol B efo re D uring A fter G e n e r a l S ize M eans L . S . D . ** @ .0 5 @ . 01 Feb. 27 M a r. 10.8 12.4 10.3 12.6 11.2 9 .9 13.3 11.4 15.0 16.0 16.9 14.0 10.6 12.4 15.5 3 .9 4 .9 7 .0 20 A p r. A pr. 10 27 (C e n tim e te rs ) May 11 —* - - -- 8.8 11 . 0 12.8 10.6 13.0 14.7 16.2 14.3 6 .9 8.9 10.8 14.6 5 .8 4 .6 8.2 1 2 .4 10.5 3 .8 3 .2 4 .2 3.0 4 .0 3.5 3 .4 2 .9 4 .0 7 .0 5 .8 8.8 7 .0 8 .9 10.9 6.9 5 .7 3 .7 6.2 2.8 9 .0 6.1 6 .7 7 .8 5.0 6.8 12. 1 10.2 3 .7 5 .4 7 .4 11.3 3.7 4 .9 3 .2 4 .3 -- -- * T im e of a p p licatio n in r e s p e c t to cool w e a th e r. * * L . S . B . v a lu e s apply to any tim e of application m ean s within size g r o u p s , but not to g e n e r a l s iz e means# 59 T a b le 12, The E ffe c t of T im e of A pplication of 15 P P M 2 ,4 - D On th e A v erag e Height of L arg e , M edium and S m all W in tered O v er Cabbage (V a r ie ty Golden Acre)* D a te s of M e a s u re m e n ts S ize of P la n t s T im e of Application* Feb. 27 M ar. 20 L arge C ontrol B e fo re D uring A fter 10.8 11.6 11.6 9 .7 12.4 13.2 13.5 12.5 16.7 15.0 10.9 12.9 15,7 3.9 7*6 7*2 7 .3 4 .9 9 .0 7 .0 9 .0 11.0 8.0 10.9 12.8 12.8 9 .4 11.8 13.9 13.0 16.8 18.4 17.8 6 ,5 7 .2 10.2 12. 1 16.5 3 .7 3*6 3 .9 3 .4 4 .2 4 .1 4 .6 4 .2 5 .8 8.2 12.4 6.2 7 .8 8 .9 9-2 11.6 6.9 6 .7 12.8 G e n e r a l Size M eans 3 .6 4 .3 6 .4 8 .5 12.4 @ .05 @ .01 2 .9 4 .0 3 .7 4 .9 3 .2 4.3 G e n e r a l S ize M eans M edium C ontrol B efo re D uring A fter G e n e r a l S ize Means S m a ll L .S .D .* * * Control B e fo re D uring A fter Apr* A p r. 10 27 (C e n tim e te rs ) 15.0 Ms Hm May 11 __ 16. 1 — 12.7 _ _ T im e of app licatio n in r e s p e c t to cool w e a th e r . ** L . S . D . v a lu e s apply to any tim e of application m ean s within size g r o u p s , but not to g e n e ra l s iz e means* - 60 - d u rin g cool w e a th e r w e r e h ig h e r th a n the co n tro l p la n ts . The r a t e s of gro w th o r th e u ltim a te h eig hts of th e s m a ll p lan ts w e re not m a t e r i a l l y a l t e r e d by th e t r e a t m e n t s em p lo yed . It is of in t e r e s t to note th a t p la n ts s p r a y e d with C1PP d u rin g cool w e a th e r w e r e the h ig h e st in each siz e g ro u p . 2 ,4 - D T r e a tm e n t s The growth r a t e s of la r g e p lan ts sp ra y e d with 2 ,4 - D at d i f ­ f e r e n t t i m e s w e r e s ta t i s t i c a l l y alike (T able 12). Medium s iz e p lan ts s p r a y e d b e f o r e , d u rin g , o r a f te r cool w e a th e r w e r e h ig h e r th a n the c o n tro ls on each m e a s u r e m e n t d a te . On A pril 10, plan ts s p ra y e d a f te r cool w e a th e r and p la n ts in the control d iffered g re a tly in h eig h t. At no tim e d u rin g th e growing s e a s o n w e re the heights of the s m a ll t r e a t e d p la n ts d iffe re n t f r o m th e co n tro l p la n ts . With 2 ,4 - D , as w ith C1PP, th e p la n ts s p ra y e d durin g cool w eath e r w e re as high o r h ig h e r th a n the p la n ts among the o th e r t r e a t m e n t s . H ead-C o r e Ratio An a n a ly s is of th e h e a d - c o r e r a t i o s of la r g e , m ed iu m and s m a ll t r e a t e d p la n ts show no im p o rta n t d iffe re n c e s re s u ltin g f r o m the s u b s ta n c e s em ployed o r the ti m e s of app licatio n . p r e s e n t e d in T a b le 13. T h e se data a r e T h e r e was a tr e n d , how ever, for th e a v e r a g e r a t i o s of the s m a ll p la n ts to be l a r g e r th an th o s e of th e m ediu m o r l a r g e p l a n ts . L a r g e p la n ts w e r e expected to have s m a ll r a tio s as t h e s e p la n ts w e r e sufficiently l a r g e at the beginning of cool w eath e r - 61 - T a b le 13. The Influence of T im e of Application of 250 P P M C1PP and 15 P P M 2 ,4 - D On the H e a d - C o r e R atio and the Growth P h a s e Index in L a r g e , M edium and S m all W in te re d -O v e r Cabbage (V a rie ty Golden A c re ). G row th S u b stan c es C h e m ic a l T im e of ApSym bol plication* Head - C ore Ratio Size of P la n ts L a r g e M edium Sm all C on tro l 1.26 1.38 1.40 3 .0 2 2.35 2 .2 5 B e fo re D uring A fter 1.28 1.39 1.34 1.32 1.41 1.32 1.39 2.98 2.98 2 .3 5 1.20 1.26 2.95 2.38 2 .4 5 2 .6 5 2 .2 5 B e fo re D uring A fter 1.28 1.35 1.28 1.36 1.33 1.29 1.42 1.43 1.33 2.52 2 .5 8 3.4 2 2.15 2.05 3.00 2.10 @ -05 @ . 01 N .S . N .S . N .S . 0.73 0.73 0.73 0.98 0.98 0,98 2.92 2.41 2,40 C1PP 2 ,4 - D L .S .D . S ize of P la n t M eans 1.27 * In r e s p e c t to cool w e a th e r . 1.34 1.39 Growth P h a s e index Size of P la n ts L a r g e M edium S m all 2.60 2 .3 8 2,70 - 62 to p r o d u c e s e e d s t a l k s . G row th P h a s e Index As m ight b e ex p ec ted , the la r g e p la n ts had high grow th p h ase in d ic e s sin c e th e y w e r e th e p la n ts m o st lik e ly to b o lt. T he a v e ra g e grow th p h a s e index of no t r e a t m e n t in any size group d iffe re d s t a t i s ­ t i c a ll y f r o m c o rre s p o n d in g c o n t r o l s . H ow ever, the a v e ra g e index fo r th e l a r g e and m e d iu m s iz e p lan ts s p ra y e d with 2 ,4 - D a f te r cool w e a th e r w as c o n s id e r a b ly g r e a t e r th a n th e indices fo r the p lan ts sp ra y e d with 2 .4 - D b e f o r e o r d urin g cool w e a th e r . If the d ata fr o m each s iz e group a r e c o n s id e r e d to g e th e r th ey sug g est th a t the tim e of application of 2 . 4 - D had an effect upon the p h a se of grow th. A pparently 2 ,4 -D ap p lied a f te r sufficient cold fo r p a r t i a l induction tended to stim u la te th e r e p r o d u c tiv e p h a s e . - 63 - EXPERIM ENT 4, 1950 T h e u ltim a te o b je c tiv e s of e x p e rim e n t 4 w e re id e n tic a l with t h o s e of e x p e r im e n t 3 . The cold tr e a t m e n t was d ifferen t than th a t em p loy ed in e x p e rim e n t 3 . MATERIALS AND METHODS V a r ie ty , seeding d a t e s , s iz e of p lan ts at th e beginning of the cold t r e a t m e n t , and th e grow th su b sta n c e s fo r th is e x p e rim e n t w e r e th e sa m e as d e s c r ib e d in e x p e rim e n t 3 . One e s s e n tia l d iffe re n c e how ­ e v e r w as th a t the p la n ts w e re subjected to a cold s to ra g e t r e a t m e n t , w hile in th e p re c e d in g e x p e rim e n t th e y w e r e exposed only to th e cool w e a th e r w hich p r e v a i le d u n d er n a t u r a l field conditions* L a r g e , m e d iu m and s m a ll p lan ts shown in F ig u r e 3 w e re t r a n s p l a n t e d f r o m th e seed lin g fla ts to 4 -in c h clay pots O cto b er 3, 1949* N o v e m b e r 2, 1949 and N o v em b er 23, 1949, resp ectiv ely * Seventy p la n ts w e r e potted fo r each of th e tw en ty -o n e tr e a tm e n ts * All p lan ts w e r e p la c e d in a cold s to r a g e ro o m on J a n u a ry 4, w h e re th e t e m p e r ­ a t u r e w as m a in ta in e d at 38° 2° F « , and held fo r fo rty -tw o d a y s . The cold s to r a g e ro o m m e a s u r e d 12 x 16 feet and was eq u ip ­ ped w ith a 2 4 -in ch ro ta tin g fan which r a n continuously giving a u n ifo rm t e m p e r a t u r e throughout th e r o o m . In o r d e r to supply adequate light f o r th e p la n ts , 4 0 -w att M azda bulbs w ire d in s e r i e s w e re p laced t h r e e fe e t a p a r t and two feet above th e p la n ts . f o o t- c a n d le s of l i g h t . T h is lighting gave 25 to 30 L ig h ts w e r e tu r n e d on at seven o*clock each - 64 - F ig u r e 3. C o m p arab le s iz e s of cabbage plants at the b e g in ­ ning of c o ld -in d u ctio n . 3. S m all p la n ts . 1. L a rg e p la n ts . 2. Medium p la n ts . - 65 - m o rn in g and off at five o 'c lo c k each evening by m e an s of an au to m atic tim e r. The above outlined cold s to r a g e t r e a t m e n t is h e r e a f t e r r e f e r ­ r e d to as th e co ld -in d u ctio n t r e a t m e n t . P la n t s re c e iv in g th e grow th su b stan ces b efo re co ld -in d u ctio n t r e a t m e n t w e re s p r a y e d D e c e m b e r 20, 1949* P la n ts re c e iv in g the grow th s u b s ta n c e s d u rin g cold -in d u ctio n w e re sp ra y e d J a n u a ry 23, 1950. The p la n ts re c e iv in g the growth su b sta n c e s a fte r the c o ld -in - d u ction t r e a t m e n t w e r e s p ra y e d F e b r u a r y 15. P la n ts which re c e iv e d th e a p p lic a tio n of growth s u b sta n c e s during induction w e re moved to a n o th e r ro o m , s p ra y e d , allowed to d r y for two h o u rs , and th e n r e ­ tu r n e d to th e cold s to r a g e ro o m . All p la n ts w e re moved f r o m the cold sto ra g e ro o m F e b r u a r y 14, and t r a n s p l a n te d to th e field F e b r u a r y 21. in ra n d o m o r d e r in each of five blocks* T r e a tm e n t s w e re a r r a n g e d E ach t r e a tm e n t in the f i r s t fo u r b lo c k s contained five p lan ts which w e re u sed fo r the p u rp o s e of co llectin g d ata on p lant grow th and d evelopm ent. The fifth b lock c o n ­ ta in e d fifty p la n ts of each tr e a t m e n t and was r e s e r v e d fo r m o r p h o ­ lo g ical s tu d ie s . C u ltu ra l p r a c t i c e s em ployed in th is e x p e rim en t w e r e id e n tica l with e x p e r im e n ts 2 and 3. In addition to collecting the data d e s c r ib e d fo r th e p re c e d in g e x p e r im e n ts , d ates of seed stalk e m e r g e n c e , flo w e rin g , and pod m a tu r ity w e r e r e c o r d e d fo r each t r e a t m e n t . T here w as no need fo r a s ta t is tic a l evaluation of th e s e data sin ce p lan ts in c e r t a i n t r e a t m e n t s p ro d u ced see d sta lk s while o th e rs did n o t. - 66 RESULTS C1PP T r e a tm e n t s D ata with, r e s p e c t to the effect of th e tim e of applying C1PP on th e grow th in height of th e t h r e e s iz e s of p la n ts a r e p r e s e n te d in T ab le 1 4o To show th e e x t r e m e d iffe re n c e s obtained among the tr e a tm e n t s in th is e x p e r im e n t, th e s e d ata a r e also shown g ra p h ic a lly in F ig u r e 4. T he p o in ts on th e b a r grap h in d icate th e a v e ra g e height of the p lan ts fo r ea c h t r e a t m e n t on th e d a te s sp ecified in the legend. The v e r ti c a l d is ta n c e betw een th e points in d icate the in c re m e n ts in plant height b etw ee n m e a s u r i n g d a t e s . L a r g e p lants s p ra y e d b efo re c o ld -in d u c - tio n g rew at e s s e n ti a lly the sa m e r a te as th o se in the co ntro l th r o u g h ­ out the e x p e r im e n t. The la r g e plants which w ere s p ray ed during c o ld -in d u c tio n grew at a slo w er r a t e than the c o n tro l. The d if ­ f e r e n c e b etw een t h e i r a v e ra g e heights on F e b r u a r y 27 was sig n ifican t. T hey w e r e not sig n ifican tly d ifferen t on M arch 20 but w e r e on A pril 10 and A p ril 20. By A pril 27 th e d iffe re n c e s in th e a v e ra g e heights of t h e s e two t r e a t m e n t s w e r e v e r y a p p a r e n t. The la r g e p lan ts in th e c o n tro l and th o s e s p ra y e d b e fo re and a f te r cold induction w e re not m e a s u r e d a f te r A p ril 27. T h e s e p la n ts , all p o s s e s s in g flo w e rs and s eed p o d s, had c e a s e d to grow . L a r g e p la n ts sp ra y e d during cold- induction w e r e m e a s u r e d tw ice m o r e , on May 4 and May 11. T h ese p la n ts p ro d u c e d flo w ers and seed pods m uch l a t e r th an the p la n ts in th e c o n tro l plot as will be d is c u s s e d l a t e r . L a r g e p la n ts s p ra y e d with C1FP a f te r cold,-induct ion grew at - 67 - T a b le 14. The Influence of T im e of A pplication of 250 P P M C1PP On th e A ccu m u lativ e A v erag e Height of L a r g e , M edium and S m a ll Cabbage at D iffe re n t T im e s D uring the Growing S eason ( V a rie ty Golden A c r e , C o ld -In d u ced )• D ates of M e a s u re m e n ts M ar. A pr. A p r. A pr. 20 10 20 27 (C e n tim e te rs) Size of P la n t s T im e of Application* Feb. 27 L arge C ontrol B e fo re D uring A fter 11.3 9 .3 10.7 10.0 12.7 13.1 11 23.2 24.4 15.8 19.5 37.0 36.9 19.4 10.5 16.8 17.7 13.1 14.6 10.3 11.8 15.6 20.7 30.0 3 .9 3 .9 4 .0 3 .8 4 .8 4 .9 4 .9 4 .4 10.7 13.5 11.8 1 7 .4 35.0 7 .6 9 .3 19. 6 1 0. 0 13.5 20.7 46.9 50.0 19.0 4 2 .6 G e n e r a l S ize M eans 3 .9 4*8 9 .8 14.2 21.0 3 9 .6 S m a ll 2 .9 7 .7 7 .4 11.9 9 .9 18.0 7 .4 9 .4 9 .5 9 .0 9.1 11.2 2.8 2.8 2.6 3 .4 3 .4 3 .6 3 .5 (\J • 00 1 “1 11.0 May 10.6 18.9 G e n e r a l Size Means 2.8 3 .5 7 .5 9 .2 10.9 17.8 L . S . D . * * @ .05 @ . 01 1 .4 1.9 2 .3 3 .0 3.1 4 .2 5 .6 7 .8 10.7 G e n e r a l S ize M eans M edium C ontrol B e fo re D uring A fter C ontrol B e fo re D u rin g A fter 6.6 26.6 10.8 8.0 40.0 - 16.2 - ' * T im e of app licatio n in r e s p e c t to co ld -in du ction . ** L . S . D . v alu es apply to any tim e of application m ean s within size g r o u p s , but not to g e n e ra l s iz e m e a n s . - 68 - LARGE. SIZL i SMALL SIZE. M L D I U M SIZE. MAY MAY AP R AP R APR MAR I 11 4 27 20 10 20 FLB U a a 2 a I— C3 = U .J aL Lt—J - Z . u - c c . y ~ r—' -= t U r tl <*: c£. <-3 ai u_ T I M L OF C l P P APPLICATION F ig u r e 4 . C o m p a ra tiv e se a so n a l growth in height of la r g e , m e d iu m and s m a ll Golden Acre cabbage plants sp ra y e d w ith 250 ppm C lP P b e fo re , during and a f te r cold induction. - 69 - a s lo w e r r a t e th a n th e c o n tro l p l a n t s . T he d iffe re n c e in the a v e ra g e h e ig h ts of th e p la n ts in t h e s e two t r e a t m e n t s was n o ticab le until A p ril 27, th e l a s t d a te of m e a s u r e m e n t . T h e r e w e r e s p e c ta c u la r d iffe re n c e s in th e r a t e of growth of th e p la n ts in th e m e d iu m s iz e group as a r e s u l t of th e tim e of applying C l P P • S uch d if f e r e n c e s did not o ccu r how ever until la te in the s e a s o n . T r e a t e d p la n ts did not d iffe r in height f r o m th e c o n tro ls until A p ril 1 0 . P l a n t s s p r a y e d b e f o r e cold-induction w e r e , on A pril 20, m uch h ig h e r th a n th e p la n ts in th e c o n tr o l. Between A pril 20 and A p ril 27, p la n ts s p r a y e d with C lP P b e f o r e cold-induction m a d e m o r e ra p id grow th in h eight th a n any of th e o th e r p la n ts in th e m e d iu m size g ro u p . P la n ts s p r a y e d d u rin g cold -in d u ctio n m a d e l e s s r a p id growth in height than th e c o n tro l p l a n t s . T h ey w e re s u b sta n tia lly lo w er in height on A pril 10 th a n th e c o n t r o l s . The d iffe re n c e in a v e ra g e heights between th is t r e a t m e n t and th e c o n tro l w as not g r e a t enough fo r s ta t is tic a l s ig n if­ ic a n c e on A p ril 27. Although s ta t is tic a l a n a ly sis was not applied to the d ata f o r th e two l a s t d a te s of m e a s u r e m e n t b e c a u se th e p lan ts in c e r ta in t r e a t m e n t s had c e a s e d to grow , th e d iffe re n c e in av erag e heights of th e p la n ts in th e c o n tro l and th o s e sp ra y e d during cold-induction was v e ry ap p aren t. P la n t s in th e s a m e s iz e group s p ra y e d a f te r th e th e r m o - i n d u c ­ tio n t r e a t m e n t m a d e grow th in height s i m i l a r to th e c o n t r o l s . T h e r e w e r e not outstanding d iffe re n c e s in r e s p o n s e to th e t i m e of applying C lP P exhibited by th e p la n ts in th e s m a ll size g ro u p . T h e ir - 70 - a v e r a g e h eig h ts showed no d if f e r e n c e s a r is i n g fr o m tr e a t m e n t . 2 ,4 - D T r e a tm e n t s The d ata in T a b le 15 re g a r d in g the effect of tim e of applying 2 ,4 - D on growth in height a r e p r e s e n te d in b a r graph fo rm in F ig u r e 5 . It can be s e e n at a glance th a t 2 ,4 - D inhibited growth of cold-induced p la n ts i r r e s p e c t i v e of the t i m e of ap p licatio n and plant s iz e . The a v e r a g e height of la r g e plan ts sp ra y e d b efo re co ld -in d u c tio n w as not sig n ifican tly l e s s than th a t of the control plants until A p ril 27. P la n ts in th e la r g e s iz e group sp ra y e d during or a f te r cold- induction w e r e not sig nificantly d ifferen t in height fr o m th o se of the c o n tro l at any tim e d urin g th e growing s e a s o n . P la n ts of m e d iu m s iz e s p ra y e d e ith e r b e fo re , during o r a fte r co ld -in d u ctio n w e re p r a c t i c a l l y the sa m e height as the co n tro ls up to A p ril 27. As m en tio ned e a r l i e r , the plan ts in a few of the tr e a tm e n t s in th is e x p e rim e n t had re a c h e d t h e i r u ltim a te height by A pril 27. T h e r e f o r e , the D . S . D . v alu es w e re not calcu lated fo r th e la s t date of m e a s u r e m e n t . It is a p p a re n t in F ig u r e 5 th at the p lants which w e r e s p ra y e d with 2 ,4 - D in g e n e ra l did not grow as rap id ly o r r e a c h an u ltim a te height c o m p a ra b le to the c o n tro ls . This is esp e c ia lly t r u e with p la n ts s p ra y e d b e fo re o r during co ld -in d u ctio n . Medium s iz e d p la n ts s p r a y e d a f te r cold-induction m ade the m o st rap id growth in height b etw een A pril 27 and May 11 of any of th e 2 ,4 -D t r e a t m e n t s . The sub sequent growth in height of the sm all p lan ts was not a l t e r e d by applying 2 ,4 - D e ith e r b e fo re , during or a f te r co ld -ind u ctio n . - 71 - T a b le 15. The Influence of T im e of A pplication of 15 P P M 2 ,4 - D On th e A ccu m u lativ e A verage Height of L a r g e , M edium and S m all Cabbage at D ifferen t T im e s D uring the Growing S e a ­ son (V a rie ty Golden A c re , C old-Induced)• S ize of P la n ts T im e of A pplication* Feb. 27 D ates of M e a s u re m e n ts M ar. A pr. A p r. A p r. 20 10 20 27 ( C en tim eters) C ontrol B e fo re D uring A fter 11.0 10.2 12.2 12.7 16.8 1 2 .0 9 .4 G e n e r a l S ize Means L arge May 11 10.8 14.4 18.0 15.4 23.2 18.5 24.0 21.5 37.0 26 .2 3 2 .4 3 2 .4 48.1 - 10.7 12.0 16.2 21.8 32.0 - C ontrol B efo re D uring A fter 3 .9 3 .8 4 .6 3 .4 4 .8 5.0 4 .5 4 .6 10.7 9 .9 9 .4 9 .2 13.5 12.4 11.3 17.4 15.6 13.6 14.5 46.9 26.3 24.7 3 3 .6 G e n e r a l S ize M eans 3 .9 4 .7 9 .8 12.2 15.3 32.9 S m all C ontrol B e fo re D uring A fter 2.9 3 .4 3 .2 3 .8 3 .0 7 .7 6 .4 6.3 6.9 9 .4 8 .3 9 .2 9 .2 11.2 2.6 2.8 2.8 9 .3 9 .5 9 .9 18.2 14.2 15.3 17.0 G e n e r a l Size M eans 2.8 3 .4 6.8 9 .0 1 0 .0 16.2 1 .4 1.9 2.3 3 .0 3.1 4 .2 5. 6 7 .8 8.0 M edium L .S. D. * @ .05 @ .0 1 12.7 11.8 10.7 T im e of ap p licatio n in r e s p e c t to cold-induction* * * L . S . D . v a lu e s apply to any tim e of application m eans within size g r o u p s , but not to g e n e r a l s iz e m e a n s . - 72 - LARGE SIZE MEDIUM SIZE SMALL SIZE MAY 11 | MA Y 4 APR 27 A P R £0 A P R 10 I MAR 20 | F E B 27 O Q£ H- uU Cn O ^ -z. u_ ct: O uJ o ca ZD d Li- -a: TIML OF 2 , 4 - D A P PL IC A TIO N ii F ig u r e 5. C o m p a rativ e seaso n al growth in height of l a r g e , m ed iu m and s m a ll Golden A cre cabbage plants s p ra y e d with 15 ppm of 2 ,4 - D b e fo re , during and a fte r cold induction. - 73 - As shown in F i g u r e 5, th e c o n tro ls w e re slightly higher on each d ate of m e a s u r e m e n t th a n p la n ts in e ith e r of the o th e r tr e a t m e n t s , although th e s e d if f e r e n c e s w e r e not at any tim e sig n ifican t. H e a d - C o r e Ratio It is of i n t e r e s t to c o m p a r e th e g e n e ra l size m ean h e a d - c o r e r a t i o s fo r l a r g e , m e d iu m and s m a ll p la n ts , T able 16. This m e a n a p ­ p r o a c h e d unity in l a r g e p la n ts , was 1 . 1 6 for m edium , and 1.46 for s m a ll p la n ts . The tim e of ap p licatio n of C lP P and 2 ,4 - D had no effect upon th e h e a d - c o r e r a ti o s w ithin the group of la r g e p la n ts . All th e s e p la n ts b e c a m e r e p r o d u c tiv e , p ro d u ced seed s ta lk s , flo w e rs , and se e d . T h e r e f o r e , th e a v e r a g e h e a d - c o r e r a tio of each t r e a tm e n t ap p ro ach ed unity • O utstanding d iffe re n c e s o c c u r r e d in the h e a d - c o r e r a tio s among th e v a r io u s t r e a t m e n t s in the m ed iu m size p la n ts . A significantly l a r g e r h e a d - c o r e r a tio r e s u lt e d when p lan ts w e re sp ray ed with C lP P d u rin g induction. S praying b e fo re o r a f te r cold-induction r e s u lte d in h e a d - c o r e r a ti o s c o m p a ra b le to th e c o n tro l. P la n ts receiv in g C lP P d u rin g induction had g r e a t e r h e a d - c o r e r a tio s than th o se receiv in g 2 ,4 - D during o r a f te r induction. Most plan ts sp ray ed during cold- induction with C lP P p ro d u ced r a t h e r f i r m h e a d s . In fact, all m edium s iz e p la n ts w e re re p r o d u c tiv e except th o se sp ray ed during induction with C l P P . C e n tra l c o r e s in f i r m heads w e re s h o r te r than in lo o se h ead s o r in p la n ts fo rm in g no tr u e h ead . Consequently, p lants sp ra y e d with C lP P durin g co ld -in d u ctio n had l a r g e r r a tio s th an the co n tro l. - 74 - T a b le 1 6 « H e a d - C o r e Ratio of Growth P h a s e Index in L a r g e , Medium and S m all Cabbage P la n ts as Affected by T im e of Application of 250 P P M C lP P and 15 P P M 2 ,4 - D (V ariety Golden A cre, C o ld -In d u ced ). G row th S u b sta n c e s C h em ical T im e of ApSym bol plication* Head - Core Ratio Siz e of P la n ts L a r g e M edium Sm all C ontrol 1 .0 1 1.09 1.49 7.65 6.70 2 .2 5 G rowth P h a s e Index Size of P la n ts L a r g e M edium S m all C lP P B ef o r e D u rin g A fter 1.02 1.06 1.00 1.13 1.32 1.09 1.45 1.46 1.48 7.60 6.70 7.55 6.4 8 3 .4 2 6.2 5 2 .3 5 1.48 2 .4 5 2 ,4 - D B e fo re D u rin g A fter 1.02 1.02 1 .0 1 1.20 1.16 1.14 1.49 1.50 1.36 7.35 7.45 7.55 4.80 5.08 5.20 1.55 1.58 @ .05 @ . 01 0.12 0.12 0.12 1.16 1.16 0 .1 6 0.16 0 .1 6 1.55 1.16 1.55 1.02 1 .1 6 1.46 7.41 5 .4 2 1.95 L .S .D . G e n e r a l S ize M eans * In r e s p e c t to co ld -in d u ctio n . 1.98 1.55 - 75 - M edium s iz e p la n ts s p ra y e d with 2 ,4 - D had r a t h e r la r g e h e a d c o r e r a ti o s as c o m p a re d to the c o n tro l. H e a d -c o re r a tio s of plants s p r a y e d b e f o r e induction with 2 ,4 - D w e r e la r g e but not la r g e enough to be s t a t i s t i c a l l y d iffe re n t f r o m th e co n tro l. The h e a d - c o r e r a ti o s fo r th e v a r io u s t r e a tm e n t s in the group of s m a ll p la n ts w e r e e s s e n tia lly the s a m e except th e s m a ll value fo r th o s e s p r a y e d with 2 ,4 - D a f te r co ld -in d u ctio n . This w as, how ever, of no p r a c t i c a l s ig n ifican ce sin ce e s s e n tia lly all of the sm all p lants p ro d u ced firm heads. H e a d - c o r e r a ti o s among the s e v e r a l tr e a tm e n t s within th e group of s m a ll p la n ts w e r e , in m o st in s ta n c e s , l a r g e r than the r a t i o s of th e m e d iu m s iz e p la n ts s p ra y e d during cold-induction with C lP P . As will be shown l a t e r th e heads of the plants receiv in g the l a t t e r t r e a t m e n t s w e r e l e s s v eg etativ e th an th o s e in the group of s m a ll p la n ts. Growth P h a s e Indices The growth p h a se indices v a r ie d with the size of p la n ts . The g e n e r a l s iz e m e a n was high with la r g e (7.41) and m edium plants (5 .4 2 ), but low with s m a ll p la n ts (1 .9 5 ). It is of in te r e s t also th at the low est grow th p h a se index fo r each s ize group r e s u lte d when p lants w e re sp ra y e d with C lP P during co ld -in d u ctio n . The indices among the tr e a t m e n t s within l a r g e p lants and among th o s e w ithin the group of s m a ll p lants w e re not significantly d ifferen t f r o m t h e i r r e s p e c t iv e c o n t r o l s . As p r e v io u s ly stated, all the la r g e p la n ts w e r e r e p r o d u c tiv e and m o s t of all the s m a ll p lants w e re v e g e t a ­ tiv e . a r e s u l t , th e r e s p o n s e to the v a r ie d tr e a tm e n t s within th e s e two s iz e g roups was s i m i l a r . T he grow th p h a s e indices of the m ed iu m plants v a r ie d a p p r e ­ ciab ly with th e t r e a t m e n t s (T able 16). P la n ts sp ray ed with C lP P b e fo re induction s c o r e d a lm o s t the sa m e index as th e co n tro l. The index for p la n ts s p r a y e d during induction with C lP P was much s m a l le r th a n fo r p la n ts of any o th e r tr e a t m e n t within the s ize grouping. P la n ts with an a v e r a g e index n e a r e s t th e s e p lan ts w e re th o se sp ra y e d b e fo re induction with 2 , 4 - D . tro ls. T h e s e two indices w e re significantly l e s s th a n the c o n ­ The d if f e r e n c e s betw een th e index of p lants sp ray ed with C lP P d u rin g co ld -in d u ctio n and th e indices among the rem ain in g tr e a tm e n t s w e r e s ig n ific a n t. The only m e d iu m s iz e p la nts to pro d u ce f ir m heads w e re th o se s p r a y e d with C lP P during co ld -in d u ctio n . Some effects of tim e of a p ­ p lic a tio n of C lP P upon p h a s e of growth in m ed ium s iz e p lan ts a r e shown in F ig u r e 6 . P la n ts on the left w e r e sp ray ed before; th o s e in th e c e n t e r , a f te r ; and th o s e on th e rig h t, during cold -in d uction . The p la n ts on the left p ro d u c e d flo w ers 11 days e a r l i e r than th o s e in the cen ter. P la n t s on the rig h t w e re sp ra y e d during induction and r e ­ m a in ed v e g e ta tiv e . P la n t s s p r a y e d b e fo re cold-induction with 2 ,4 -D had th e second s m a l l e s t and th o s e s p ra y e d during induction had the th i r d s m a lle s t grow th p h a s e index among the m edium size p la n ts . The index was - 77 - F ig u r e 6 . Some effects of the tim e of application of C lP P on the ph ase of growth in Golden A cre Cabbage. L eft to rig h t, s p r a y applied b e fo re , a f te r and during co ld -in d u ctio n . F ig u r e 7. P h o to g rap hed May 23, 1950. R eproductive cabbage plants show ­ ing in c r e a s e d n u m b e r of seed sta lk s re su ltin g fro m C lP P t r e a t m e n t . No. 6 . The co n tro l. N o . 7 . Sprayed b e fo re induction with 250 ppm of C lP P . 78 - s m a l l e r fo r th e p la n ts s p ra y e d a f te r cold-induction than for the c o n ­ tro ls. E v en though th e in d ices a r e s ta t is tic a lly s m a l le r in 2 ,4 - D t r e a t e d th a n in c o n tro l p la n ts , th e p r a c t ic a l value with r e s p e c t to i n ­ h ib itio n of bolting in cabbage is q u estio n ab le. All the m ed iu m size p la n ts in each of th e 2 ,4 - D t r e a t m e n t s w e re r e p ro d u c tiv e . Seed S talk D evelopm ent T h e effect of tim e of applying C lP P and 2 ,4 -D on seed stalk dev elo p m en t is shown in T ab le 17. The av e ra g e nu m b er of days f r o m the end of cold -in d u ctio n to the ap p e a ra n c e of seed stalk s v a r ie d among t r e a t m e n t s . sta lk s. P la n t s in c e r ta in tr e a tm e n t s did not p ro d u ce seed The a b s e n c e of seed s talk s was confined to the s m a ll p la n ts . C lP P T r e a tm e n ts The ti m e of ap p licatio n of C lP P affected the developm ent of f lo r a l p r i m o r d i a in cabbage (Table 17). Applying th is g r o w th - r e g u ­ la tin g su b stan ce b e fo re induction to la r g e p lants had little effect upon th e t i m e th e see d s talk s e m e r g e d . When applied during i n ­ duction seed s ta lk a p p e a ra n c e w as delayed 14 days in the la r g e p la n ts . Seed s ta lk s a p p e a re d four days l a t e r on the la rg e plants sp ra y e d a f te r induction th a n on the control p la n ts . Applying C lP P b e fo re induction h asten e d the a p p e a ra n c e of seed s ta lk s 17 days on m edium size p la nts and 14 days on s m a ll p l a n ts . When applied durin g induction, th is substance delayed a n d / o r inh ib ited seed s ta lk and flow er developm ent in la r g e , m ed iu m , and - 79 - T a b le 17, The E ffect of T im e of A pplication of 250 P P M of C lP P and 15 P P M of 2 ,4 - D On the A verage N um ber of Days f r o m C om pletion of C old-Induction to th e A ppearance of Seed S talk s and th e N um ber of P la n ts P roducing F lo w e r s , G row th S u b stan ces C h em ical T im e of Ap­ Symbol plication* 2 ,4 - D * N um ber of P la n ts P ro d u cin g F lo w e r s P lan t Size L a rg e Medium S m all 59 73 79 20 16 2 B efo re D uring After 61 65 oc 70 20 20 20 15 73 63 56 82** 67 2 0 1 B efo re D uring A fter 67 65 59 70 79 76 oc oc oc 20 20 20 C ontrol C lP P Days to Seed Stalk A ppearance P la n t Size L a r g e M edium Sm all 15 10 9 12 0 0 0 In r e s p e c t to cold -in du ction t r e a t m e n t . ** F iv e p lan ts p ro d u ced seed stalk s which b a r e l y b u r s t through the o u te r l e a v e s , but no flo w e rs w e r e p ro d u ced by any of the plants in th is t r e a t ' m e n t, and s m a ll p la n ts . Even though b a r e l y v is ib le seed, stalk s w e re p r o ­ duced on five of th e 20 m ed iu m s iz e p la n ts , they n e ith e r grew above th e n o r m a l p lan t head n o r p ro d u ced f lo w e r s . a p p e a r e d w e r e delayed as shown in T able 17. The seed s ta lk s that Seed s ta lk s p ro duced by m e d iu m and s m a ll p la n ts sp ra y e d a f te r induction w ere v isib le in each s iz e group s ix and nine days e a r l i e r , re s p e c tiv e ly , th an in the c o rre s p o n d in g c o n tr o ls . P l a n t s s p ra y e d with C lP P b efo re o r a f te r induction w e re m o r e r e p r o d u c tiv e th a n th e c o n tro l. T his in c r e a s e d re p ro d u c tiv e n e s s was noted m a in ly in an in c r e a s e in th e n u m ber of seed stalk b ra n c h e s and seed p o d s . In F ig u r e 7 a r e two r e p r e s e n ta tiv e p la n ts . The plant s p r a y e d b e f o r e induction pro d u ced n u m e ro u s seed stalk b r a n c h e s , w h e r e a s the co n tro l p ro d u ced only five o r six s p a r s e ly d is trib u te d b ran ch es. T he n u m b e r of p la n ts producing flo w ers in the m ed iu m and s m a ll s iz e s w as the sam e fo r the control p la n ts, th o se sp ra y e d b efo re and th o s e s p ra y e d a f te r induction. None of the plants in th e s e two s iz e gro u p s which w e r e s p ra y e d during induction produced f lo w e r s . 2 ,4 - D T r e a tm e n ts All la r g e p la n ts s p ra y e d with 2 ,4 - D b o lted. Seed stalk s a p ­ p e a r e d eight days l a t e r on th o se sp ra y e d b efo re and six days l a t e r on th o s e s p r a y e d d u rin g induction than on th e c o n tro ls . The n u m b e r of days f r o m the end of cold-in d u ctio n to the a p p ea ra n ce of seed stalk s - 81 - on p la n ts s p r a y e d a f t e r induction with 2 ,4 - D did not d iffer f r o m the c o n tr o l. P la n t s s p r a y e d b e f o r e induction w e re f i r s t to pro d u ce v isib le seed s ta lk s in th e m e d iu m s iz e group. th a n th e c o n t r o l s . They w e re th r e e days e a r l i e r P la n ts s p ra y e d during induction w e re six days l a t e r and th o s e s p ra y e d a f te r induction w e re th r e e days l a t e r th an th e c o n ­ t r o l p la n ts . flo w ers. A to ta l of 16 out of 20 p lan ts in the control prod u ced T en of th e 20 p la n ts sp ra y e d b e fo re , nine sp ray ed du ring , and 12 p la n ts s p ra y e d a f te r induction produced flo w e rs . N e ith e r s e e d s ta lk s n o r flo w ers w e re produced on any of the s m a ll p la n ts s p ra y e d with 2 , 4 - D . B ase d on th e s e data it a p p e a rs th a t 2 ,4 - D had an in h ib ito ry effect upon seed stalk developm ent e x ­ cept with th e t r e a t m e n t s applied to la r g e p la n ts . 82 •* EXPERIM ENT 5, 1951-52 It w as d e s i r e d to obtain additional in fo rm atio n with r e s p e c t to p ro m o tin g th e r e p r o d u c tiv e p h a se by the u s e of g ro w th -reg u latin g s u b ­ sta n c e s. In o r d e r to study th is effect an attem p t was m ade to p a r ti a ll y induce th e re p r o d u c tiv e p h a s e . Since Round Dutch is somewhat r e ­ s is ta n t to bolting it was em ployed in p r e f e r e n c e to the Golden A cre v a rie ty . MATERIALS AND METHODS S eed s of Round D utch w e re planted August 22, 1951 in the greenhouse. The seed lin g s w e re tra n s p la n te d to 4 -in ch clay pots O cto b er 1 and grown in the g reen h o u se until the ste m d ia m e te r s m e a s u r e d a p p ro x im a te ly 7 m m . T h ese plan ts w e re then divided into eight g roups of s ix te e n p lan ts each in such a way that p lants in one group w e r e as n e a r l y as p o s sib le the sa m e size as plants in any o th e r g ro u p . each. E ac h group w as th e n divided into four r e p lic a te s of four p lan ts E ach 16-plant group r e c e iv e d one of the following tr e a tm e n ts : T r e a tm e n t N u m b er C h em ical C oncentration (ppm) - T im e of Application — 1 C ontrol 2 M .H . 250 N ovem ber 26, 1951 3 M .H . 250 D e c e m b e r 20,1951 4 M .H . 250 Ja n u a ry 7, 1952 5 TIB A 250 D e c e m b e r 20,1951 6 TIB A 250 Ja n u a ry 7, 1952 - 83 - T re a tm e n t N u m b er C h em ical C o n centratio n (ppm) T im e of Application ^ C lP P 250 D e c e m b e r 20,1951 8 C lP P 250 J a n u a ry 7, 1952 All p la n ts w e r e su b jected to a cold-induction tr e a tm e n t of 36° ^ 3° F . fo r f o r ty - o n e days f r o m N ovem ber 27, 1951 through Ja n u a ry 7, 1952. O b s e rv e in th e l i s t of t r e a t m e n t s above th at growth su b stan ces w e re applied to c e r t a i n t r e a t m e n t s b e fo re cold-induction, to o th e rs during co ld -in d u ctio n and to s till o th e rs a f te r cold-induction. Lighting fo r the p la n ts throughout the induction t r e a tm e n t was the same as d e s c r ib e d in e x p e rim e n t 4. A fter the induction tr e a tm e n t , all p lants w e re r e tu r n e d to the g re e n h o u s e and tr a n s p la n te d to on e-g allo n tin cans Ja n u a ry 10. The m e d iu m in the cans co n s is te d of equal p a r t s of soil, w e ll- r o tte d m a n u r e , and w e ll - r o t te d saw d u st. T r e a tm e n ts w ere ran d o m ized in fo u r r e p li c a te s throughout the e x p e rim e n t. To in s u r e adequate n u trie n ts fo r the growing p lants 200 m l . of a n u tr ie n t solution co n sistin g of one ounce of 10-52-17 soluble f e r t i ­ l i z e r and two ounces of am m o n iu m n it r a te d isso lv ed in t h r e e and o n eh alf gallons of w a te r w as applied ev ery two weeks to each can . tin e su lfate and DDT w e r e u se d to control i n s e c t s . a p r o b le m . N ic o ­ D is e a s e s w e r e not D ata on growth and developm ent w ere collected as d e ­ s c r ib e d in p r e v io u s e x p e r im e n ts . - 84 - RESULTS The d a ta r e g a r d in g the effect of tim e of application of C lP P , TIB A and MH on plan t height a r e p r e s e n te d in T able 18. h e ig h ts w e r e e s s e n ti a lly th e sa m e J a n u a r y 17, 1952. A verage The a v e ra g e h eig h ts fo r two t r e a t m e n t s w e re on F e b r u a r y 29, s ta tis tic a lly d i f f e r ­ ent f r o m th e c o n t r o l s . P la n t s sp ra y e d with MH afte r cold-induction w e r e not as high and p lan ts which w e re sp ray ed during induction with C lP P w e r e h ig h e r th a n th e c o n tr o ls . The d ifferen c e in a v e ra g e height of th e p la n ts in th e f o r m e r t r e a tm e n t and th a t of the co ntro l was highly s ig n ific a n t. P la n ts in th e co n tro l w e re about tw ice as ta ll A pril 17 as p lan ts s p r a y e d w ith MH a f te r co ld -in d u ctio n . Spraying TIB A b efo re in d u c ­ tio n and T1BA and C lP P durin g induction produced t a l l e r p lan ts than th e c o n t r o l . The only p lan ts with av e ra g e heights significantly d ifferen t f r o m th e c o n tro l on June 11 w e re th o se sp ra y e d with MH a f te r in d u c ­ ti o n . S p rayin g with MH a f te r induction inhibited growth and p la n ts r e ­ ceiving th is t r e a t m e n t w e r e only half as high as th e c o n t r o l s . t e r m i n a l bud died in m o s t of th e s e p la n ts . m ad e li t t l e o r no g ro w th . v e r y p o o r growth* The T e r m in a ls th a t did not die S e v e ra l a x illa r y buds developed but m ade At th e end of the ex p erim en t when the d ata w e re c o lle c te d on th e h e a d - c o r e r a ti o s and growth p h ase in d ic e s , five p la n ts which had b een s p ra y e d with MH a f te r induction w e re not d i s ­ s e c te d but le ft in tact fo r f u r th e r o b s e rv a tio n of th e ir growth h a b it. The - 85 - T a b le 18. T he E ffect of 250 P P M of C e rta in G row th-R egulating S u b ­ sta n c e s on A v erag e Height of Cabbage P la n ts P a r t i a l l y Induced, to F lo w e r by Cold T e m p e r a tu r e E x p o su re (V ariety , Round D utch). G row th S u b stan ces C h em ical Symbol T im e of Ap­ plication* C ontrol Height in c m s . on dates sp ecified . J a n . 17 F e b . 29 A pr. 17 June 11 6 .4 8 13.85 16.45 20.42 B efo re D uring A fter 7.02 7.05 6.75 13.90 12.85 7.08 18.48 17.90 7.77 22.92 T1BA B efo re D uring 7 .2 5 7.05 14.85 14.98 18.80 18.85 21.85 22.42 C lP P B efo re D uring 7.45 7.4 5 13.70 15.55 18.22 18.80 20.18 @.05 N .S . 1.30 1.77 2.24 3.05 4.2 5 5.79 MH L .S.D o @.01 * T im e of ap p licatio n in r e s p e c t to cold—induction* 20.82 10.35 22.02 a v e r a g e height of th e s e five p la n ts tw elve m onths a f te r t r e a tm e n t was 15 .6 c m s . D u rin g th is tw elve month p e rio d n e ith e r heads n o r seed sta lk s developed on e ith e r of the five p la n ts . D ata c o n ce rn in g tim e of applying MH, TIB A and C1PP on the h e a d - c o r e r a tio and growth p h ase index of p a r tia lly induced p lan ts a r e shown in T ab le 19« Applying MH b efo re cold-induction had no m a ­ t e r i a l effect on th e h e a d - c o r e ra tio but significantly in c r e a s e d the grow th p h a s e index o v e r th e co n tro l. The d ifferen ce between each of t h e s e two v a lu e s and the co rresp o n d in g valu es for the co n tro ls w ere v ery apparen t. S praying p lants e ith e r b efo re o r a fte r induction with T1BA c a u se d no change of the h e a d - c o r e ra tio o r growth phase index. The h e a d - c o r e r a tio was red u ced and the growth p h ase i n ­ dex i n c r e a s e d by sp ray ing p la n ts b e fo re induction with C1PP. The d iffe re n c e in h e a d - c o r e r a tio s betw een the control and p lan ts sp ra y e d with C1PP b e fo re induction was outstanding. Growth phase indices fo r th e s e two tr e a t m e n t s w e re significantly d iffe re n t. The h e a d - c o r e r a ti o and the grow th p h ase index of plan ts sp ra y e d during induction w e r e e s s e n tia lly th e sa m e as the c o n tro l. The a b s e n c e f r o m T able 19 of the data p ertain in g to plants s p r a y e d with MH a f te r induction should be noted. T hese data w e re o m itte d f r o m th e s t a t i s t i c a l a n aly sis and w ere not included in the ta b le . The h e a d - c o r e ra tio for this tr e a tm e n t was 1. None of the grow th p h a s e in d ices em ployed in th e se studies fit the p la nts in th is t r e a t m e n t and the p la n ts w e re not s c o re d . 87 - T a b le 19. H e a d - C o r e R atio and Growth P h a s e Index of Cabbage P la n ts P a r t i a l l y Induced to F lo w e r by Cold T e m p e r a tu r e E x p o s u re as Influenced by T im e of Application of MH, TIB A, and C1PP (V a rie ty Round Dutch) 0 G row th S u b stan ces C h em ical Symbol PPM C ontrol H ead-■Core Ratio T im e of Application* B efo re During 1.86 - Growth P h a s e Index T ime of Application B efore D uring 2.1 - MH 250 1.68 1.29 3.1 4 .5 TIB A 250 1.71 1.76 2 .6 2.1 C1PP 250 1.42 1.72 3 .2 2 .2 L . S . D . * * @.05 @.01 ^ 0.23 0.31 1.0 1 .4 T im e of ap p licatio n in r e s p e c t to the cold-induction t r e a tm e n t , ** L . S . D . v a lu e s apply to tim e of application m e an s within and among c h e m ic a ls , T h e g e n e r a l a p p e a ra n c e of plants among the tr e a tm e n t in th is e x p e r im e n t v a r i e d li ttl e except th o s e sp ra y e d with MH during and a f te r in d u ctio n. T h e r e w as a lso v a r ia tio n among p la n ts t r e a t e d with MH du rin g in du ctio n . M ost p la n ts sp ra y e d during induction w e re r e p r o ­ ductive in a p p e a ra n c e but none of th e m p ro du ced f lo w e r s . The p h o to ­ g ra p h s shown in F ig u r e 8 il lu s tr a t e the type of growth m ade by th e s e MH s p r a y e d p la n ts . The plant r e p r e s e n te d by D was the co n tro l. Note th e w ell f o r m e d h e a d . form head s. P la n t s sp ra y e d during induction with MH did not T h e d e g r e e of ap p aren t re p ro d u c tiv e n e s s in th is tr e a tm e n t v a r i e d as shown in A and B. The plant shown in A had all a p p e a ra n c e s of a r e p r o d u c tiv e plant except fo r the production of f lo w e r s . The plant shown in C was r e p r e s e n ta tiv e of th o se sp ray ed with MH a fte r in d u c ­ tio n . Note the dead t e r m i n a l bud and young w ith e re d le a v e s . Four l a t e r a l buds developed on th is plant but th r e e w e re rem o v e d ju s t b e ­ f o r e th is pho to g rap h was m a d e . - 89 - B F ig u r e 8 . P a r t i a l l y induced cabbage p lan ts following t r e a t m e n t w ith MH. co ld -in d u c tio n . A and B s p ra y e d during; and C a fte r D, c o n tro l. - 90 - MORPHOLOGICAL STUDIES T h e s e s tu d ie s w e r e m ad e with t h r e e ob jectiv es: (1) to a s c e r t a i n th e m o rp h o lo g ic a l changes o c c u r r in g in the te r m in a l growing points w hile th e p la n ts w e re being co ld -in d u ced , and a f te r induction; ( 2 ) to d e t e r m in e th e changes in t e r m i n a l growing points cau sed by applying g r o w th - r e g u la tin g s u b s ta n c e s at v a r ie d ti m e s with r e s p e c t to th e coldinduction t r e a t m e n t ; and, (3) to d e te r m in e th e tim e of seed stalk i n i ­ tia tio n am ong the v a r io u s t r e a t m e n t s . Such studies should r e v e a l the m o rp h o lo g ic a l changes a s s o c ia te d with the tr a n s f o r m a tio n fr o m the v e g e ta tiv e to th e re p ro d u c tiv e growth p h a s e , tim e of d ifferen tiatio n of th e s e e d s ta lk and f lo w e r s , and any in te r n a l changes a s s o c ia te d w ith a p p lic a tio n of g ro w th -re g u la tin g s u b s ta n c e s . MATERIALS AND METHODS S am p les c o n sistin g of te r m i n a l shoots * w e re h a r v e s te d p e r io d ic a lly throughout the s e a s o n f r o m each tr e a tm e n t in the th r e e e x p e r im e n ts conducted d urin g th e 1949-50 s e a s o n . The f i r s t s a m p le s w e r e co llected D e c e m b e r 12, 1949, and subsequent sa m p le s at a p ­ p r o x im a te ly 15 day in te r v a ls th ro u g h A pril 14, 1950. E ach sam p le c o m p ris e d four t e r m i n a l sh o o ts. A fter the le a v e s and r o o ts w e re rem o v e d f ro m the s e le c te d p la n ts , e x c e s s t i s s u e was t r i m m e d , with a s h arp knife, f r o m around * See T e rm in o lo g y , page 24. 91 th e t e r m i n a l shoots* The t e r m i n a l shoots w e re then p laced in v ia ls containing f o r m a l in - ace to - alcohol (FAA) solution for killing and fixing* E ac h 100 ml* of FAA fo rm u la u sed co n sisted of 6 .5 ml* of f o r m a l in , 2*5 m l . of a c e tic acid and 91 m l. of 50 p e rc e n t ethyl a l ­ cohol. The length of th e p r e s e r v e d shoots v a r ie d f r o m 8 to 12 mm* depending on th e s iz e of plan t and c h a r a c te r of grow th. A ir w as re m o v e d f r o m th e sp ecim en s in the v ia ls by m ean s of a su ctio n p u m p . V ials containing the sp ecim en s w ere left in th e v acu u m c h a m b e r until th e t e r m i n a l shoots sank to th e bottom of th e k illin g and fixing solution with the vacuum off, which u s u a lly r e ­ q u ir e d 20 to 30 m in u te s . The v ia ls w e re th en sealed with a i r tight lid s and s to r e d until F e b r u a r y , 1951, A fter w ashing in running w a te r for t h r e e h o u rs th e t e r m in a l shoots w e r e d e h y d ra te d by th e alcohol-xylene method as d e s c r ib e d by Jo h a n s e n (42). T h e s e shoots w e re em bedded in p a ra ffin and s e c ­ tio n ed lo ng itu d in ally at a th ic k n e s s of seven m ic ro n s with a r o t a r y m ic ro to m e . T e n to t h i r ty n e a r - m e d ia n sectio n s w ere saved f r o m the rib b o n of each shoot and mounted on s lid e s . After d ry in g, the p a r a f f in in and a ro u n d th e sectio n s was rem o v ed with x y len e. The s e c tio n s w e r e stain ed in s a fra n in and aniline blue with D e la fie ld fs h em ato x y lin a s d e s c r ib e d by P opham (67), and mounted in b a l s a m . The se c tio n s w e r e studied u n d er a low and high pow er and oil e m e r ­ sion m i c r o s c o p e . G r o s s and d e ta il m orph o lo g ical changes induced by v a r io u s t r e a t m e n t s w e r e o b s e r v e d . - 92 - The m o rp h o lo g ic a l study r e p o r te d h e r e i n was conducted with th e l a r g e , m e d iu m and s m a ll p la n ts s p ra y e d with 250 ppm of C1PP and 15 ppm of 2 ,4 - D b e f o r e , durin g and a f te r th e cold-induction t r e a t ­ m en t as d e s c r i b e d in e x p e r im e n t 4 , S tudies w e re lim ite d to th is e x ­ p e r i m e n t sin ce no p la n ts in o th e r e x p e rim e n ts w e re com pletely in th e r e p r o d u c tiv e p h a s e . In a ll, about 110 d ifferen t sam p les w e re studied including about 440 t e r m i n a l sh o o ts. T he grow ing point* was divided into a zonal p a tte r n fo r s i m ­ p lic ity in d is c u s s in g the m o rp h o lo g ical s tu d ie s . The d ia g ra m m a tic r e p r e s e n t a t i o n shown in F ig u r e 9 will fa c ilita te an u n d erstan d in g of the lo c a tio n of each of th e fo u r zo n e s . The tunica co n sistin g of only the two s u r f a c e cell l a y e r s is r e p r e s e n te d in zone 1. in itia ls a r e r e p r e s e n t e d in zone 2. The co rp u s The p e r ip h e r a l o r flanking t i s ­ sue is r e p r e s e n t e d in zone 3, and the rib m e r i s t e m in zone 4. T his m ethod was em ployed with re a liz a tio n th at c e r ta in t i s s u e s w e re not e a s il y d if f e r e n tia te d f r o m o t h e r s . F o r exam ple, a d istin ctio n b e ­ tw een th e tu n ic a and co rp u s in th e shoot apex* was not e a s ily m a d e . T h e r e w as a g ra d u a l tr a n s i t i o n f r o m one ti s s u e to the o th e r r a t h e r th a n a d is tin c t line of d e m a r c a tio n s e p a ra tin g th e m . To f u r th e r sim p lify th e d is c u s s io n th e cell l a y e r s will o ccasio n ally be r e f e r r e d to as th e f i r s t , second, th i r d , fourth and so fo rth , p r o g r e s s i n g fr o m 1 See T e rm in o lo g y , page 24. F ig u r e 9. D ia g r a m m a tic r e p r e s e n ta tio n showing four d is tin c tiv e zones in the v eg etativ e growing point of cabbage. 1. Tunica l a y e r . 2. C orpus in itia ls . 3. P e r i p h e r a l o r f la n k ­ ing t i s s u e s . 4. Rib m e r i s t e m . F ig u r e 10. The growing point of a vegetative cabbage plant h a r v e s te d F e b r u a r y 6 . (a) Tunica la y er; (b) corpus in itia ls ; (c) p r o c a m b ia l c ells; (d) rib m e r is te m ; (e) young developing le a f. x64 -94 - th e s u r f a c e l a y e r in w a rd . RESULTS F a m i l i a r i t y with the changes th a t o c c u r in th e veg etativ e and r e p r o d u c tiv e grow th p h a s e s as the p la n ts developed fr o m seed lin gs to m a tu r ity w as the f i r s t o b je c tiv e . A fter th is was acco m p lish ed any changes th a t m ight b e cau sed by the applied g ro w th -reg u latin g s u b ­ sta n c e s could b e m o r e r e a d ily d e te c te d . S easo n al Changes in the T e r m in a l Growing Point of V egetative P la n ts Only slight changes w e r e found in p lan ts within a t r e a tm e n t betw een D e c e m b e r 12, 1949, and F e b r u a r y 6 , 1950. On each sam p lin g d ate th e growing points in the la r g e p lants w ere l a r g e r th a n in th e m e d iu m p la n ts and in like m a n n e r th o se in the m edium p la n ts w e r e l a r g e r th a n in th e s m a ll p la n ts . T h e re was little d if ­ f e r e n c e in s iz e of growing points in p la n ts of the sam e size and l i ttl e change o c c u r r e d in th e growing points during the c o ld -in d u ctio n t r e a t m e n t . A fter the p la n ts w e re tr a n s p la n te d to the field th e ap ices b e ­ cam e m o r e a c tiv e . In F ig u r e 10 can be seen a p h o to m icro g rap h of a r e p r e s e n t a t i v e of th e v eg etative p la n ts on F e b r u a r y 6 , 1950, about six w eeks p r i o r to the tim e of activ e plant grow th. th e d iffe re n t t i s s u e s w e r e about the s a m e s iz e . w e r e d is ti n c t. The c e lls in C ells in the tunica C ells in the t h i r d and fourth cell la y e r s w ere l e s s - 95 - d istin c t. The p r o c a m b iu m c e lls w e r e m o r e active than the corpus in itia ls as evidenced by d if f e r e n tia l stain in g . The rib m e r i s t e m cells w e r e a r r a n g e d in a n o n - d e s c r ip t iv e m a n n e r , and a p p ea re d to have b e e n dividing in v a r io u s p la n e s . When active growth s ta r t e d a f te r M a rc h 20, a c tiv ity i n c r e a s e d in each of the four zones (F ig u re 11). The c e lls in th e tu n ica divided rap id ly in an an ticlin al plane (cell wall f o r m e d in a p lan e p e r p e n d ic u la r to the o u te r s u rfa c e ). ti a l s divided r a p id ly in v a rio u s p la n e s. C orpus i n i ­ C ells in this zone w e re e a s ily d is tin g u is h a b le f r o m th o s e of adjoining z o n es. The d iv isio n of the c e lls in th e t h i r d and fo u rth cell l a y e r s in the o u te r p a r t of zone 3 n e a r the shoot apex w as p r i m a r i l y a n ticlin ally . H ow ever, o c c a s io n a lly , p e r ic lin a l d iv isio n s o c c u r r e d as will be d is c u s s e d la te r. T he p ro c a m b iu m c e lls w e re dividing rap id ly in a p e r ic lin a l plan e (cell wall f o r m e d in a plane p a r a l le l with the o u te r su rface) and th e s e c e lls w e r e l e s s d is tin c t th a n b efo re active growth began. d iv isio n in zone 4 o c c u r r e d in v a rio u s p la n e s . Cell The cells in each zone w e r e sligh tly l a r g e r and th e ap ice s w e re b r o a d e r than b efo re th e tim e of activ e grow th. As can be se e n in F ig u r e 12, no m a jo r g r o s s change o c c u r r e d in th e t e r m i n a l growing point of v egetativ e plan ts a f te r growth s ta r te d in the s p r in g . T h is shoot was collected A pril 14. Shoots collected a f te r th is date showed th a t no g r o s s changes had o c c u r r e d in the g ro w ­ ing p o in ts, o th e r than a slight in c r e a s e in s iz e , as the plant heads r e a c h e d m a r k e t m a tu r ity . - 96 - F ig u r e 11. The growing point of a vegetative cabbage p lant h a r v e s te d M arch 27. (a) Tunica la y er; (b) corpus i n ­ itia ls ; (c) p r o c a m b ia l cells; (d) rib m e r i s t e m . F ig u r e 12. x 64 The growing point of a vegetative cabbage p lant h a r v e s te d A pril 14. x64 - 97 - L e a f D evelopm ent C e lls in th e tu n ica divided an ticlin ally without exception. T hose in th e t h i r d and fo u rth cell l a y e r s divided an ticlin ally except d u rin g the in itia tio n of a le a f o r o th e r l a t e r appendage. In the beginning of le af ■initiation c e lls in th e t h i r d and fourth l a y e r s ju s t to e ith e r side of the c o rp u s in itia ls and in zone 3 began to divide p e r ic lin a lly to fo r m the le a f i n i t i a l s . u r e 13. E a r l y evidence of th is phenom enon can be seen in F i g ­ Continued p e r ic lin a l d iv isio n s followed s h o rtly by p e r ic lin a l and a n tic lin a l d iv isio n s r e s u lte d in the fo rm atio n of a le a f p r im o r d iu m , F ig u r e 14. T h e c e lls in the tunica continued to divide an tic lin a lly . In th e le a f p r im o r d iu m , F ig u r e 15, cells divided in v a rio u s plan es f o r m ­ ing slight " h u m p s ' 1 to e i th e r side of th e shoot apex. In F ig u r e 16 can be seen a p h o to m ic ro g ra p h of a cabbage te r m in a l growing point with young developing le a v e s and advanced le a f p r im o r d ia . Some Changes Which O ccur in the T e rm in a l Growing P o in t of R eproductive P lan ts S e v e ra l o b s e r v a b le g r o s s changes o c c u r r e d in the te r m in a l shoots d u rin g th e tr a n s i tio n a l s ta g e s f r o m the veg etativ e to the r e ­ p ro d u c tiv e p h a s e of gro w th . In th e e a r ly stag es of th is gradual t r a n s f o r m a t i o n it w as difficult to m o rphologically d etect with c e r ­ ta in ty when th e re p r o d u c tiv e p h ase was in itia te d . F o r exam ple, the t e r m i n a l growing point r e p r e s e n te d in F ig u re 17 only dep icted in d i­ catio n s th a t th e r e p ro d u c tiv e p h ase was being in itia te d . The l a t e r a l - 98 - F ig u r e 13. L ea f in itiatio n in a vegetative cabbage plant, (a) Shoot apex; (b) co rp us in itia ls; (c) tunica la y er; (d) le af in itia l in th i r d and fourth cell l a y e r s . x620 a b F ig u r e 14. D evelopm ent of a leaf p rim o r d iu m in a vegetative cabbage p l a n t s (a) T unica la y e r; (b) le a f p rim o r d iu m developing by p e r ic lin a l cell d iv isio n . x620 - 99 - a b F ig u r e 15. The growing point of a vegetative cabbage plant showing a le a f p r im o r d iu m . (a) L ea f p rim o rd iu m ; (b) o ld er le a f, x l 28 F ig u r e 16. The growing point of a vegetative cabbage plant showing le a f d ev elo p m en t, vanced le a f p r im o r d iu m . (a) Young developing leaf; (b) a d ­ x l2 8 - 100 - F ig u r e 17. The growing point of a cabbage plant h a rv e s te d F e b r u a r y 6 which is p ro b ab ly re p ro d u c tiv e , (a) Cells form ing in longitudinal row s; (b) le a f p rim o rd iu m ; (c) la t e r a l growing point. x64 F ig u r e 18. The growing point of a re p ro d u ctiv e cabbage plant h a r v e s te d F e b r u a r y 24. (a) L a t e r a l growing point p r im o r d iu m d e ­ veloping in the axil of a le a f p rim o rd iu m ; (b) an older growing point p r im o r d iu m ; (c) c e lls form ing in longitudinal ro w s. x64 - 101 - grow ing p o in ts w e r e beginning to d iffe re n tia te and grow in the a x ils of each of two le a f p r i m o r d i a . The c e lls in the rib m e r i s t e m zone u n d e r ­ n e a th th e co rp u s in itia ls w e r e beginning to f o r m in longitudinal row s when th i s s p e c im e n w as c o lle c te d . As will be seen l a t e r , the growth of th e l a t e r a l growing points and th e tendancy of cells to be a r r a n g e d in longitudinal row s in zone 4 w e re two g r o s s changes found in th is study to be d e fin itely a s s o c ia te d with the rep ro d u ctiv e p h a s e . In c o n t r a s t to th e n u m e ro u s stu d ie s r e p o r te d for m any c r o p s , the shoot a p ic e s of th e cabbage p la n ts exam ined in th is study did not becom e "fla tte n e d and b ro a d e n e d at the tip " p r i o r to seed stalk or f lo ra l i n i ­ tia tio n but r e m a in e d slig htly d o m e -sh a p e d throughout the study i r ­ r e s p e c t iv e of th e grow th p h a s e . G r o s s changes o c c u r r in g in the growing point in the e a r ly s ta g e s of in itia tio n of the re p ro d u c tiv e ph ase can be seen m o re c l e a r l y in F ig u r e 18. p o in ts . G rowth had in itiated in a few l a t e r a l growing C ells in th e r ib m e r i s t e m zone w e re being a r r a n g e d in m o r e d is tin c t longitudinal row s when th is shoot was co llected . On th e left side of th e t e r m i n a l growing point ju s t beneath the apex was a le a f p r im o r d iu m w ith a l a t e r a l growing point p r im o r d iu m in its ax is. Note th a t the p r im o r d iu m of the l a t e r a l growing point had m ade about th e sam e growth as th a t of the le a f. The two u p p e rm o st l a t e r a l growing point p r i m o r d i a shown in F ig u r e 19 had also m ade growth equal to t h e i r ad jacen t le a f p r i m o r d i a . The te r m in a l growing point shown in F ig u r e 19 w as slig h tly m o re advanced in the rep ro d u ctiv e - 102 - F ig u r e 19. The growing point of a rep ro d u ctiv e cabbage plant h a r v e s te d M arch 10. m o r d iu m . (a) L a t e r a l growing point p r i ­ x64 F ig u r e 20. The growing point of a rep rod u ctiv e cabbage plant h a r v e s te d M arch 27 showing a p ro b ab le flower p r i m o r ­ d iu m . (a) L e a f making lim ite d growth; (b) probable flower p r im o r d iu m . x64 - 103 - p h a s e th a n th e one shown in F ig u r e 18. The younger le av es w e re not developed so w ell in the shoot shown in F ig u r e 19 as in F ig u r e 18. The c e lls in th e r ib m e r i s t e m w e r e in longitudinal ro w s. In F i g u r e 20 is shown an advanced stag e in the re p ro d u c tiv e grow th p h a s e . L a t e r a l growing points had been initiated throughout the length of the shoot. M ore newly developed le av es had m ade lim ite d grow th and c e lls in the rib m e r i s t e m w ere in longitudinal row s. As w ill be shown in d etail l a t e r in th is d is c u s s io n it was d if ­ ficult to d is tin g u is h betw een a flo ra l in itial o r p r im o r d iu m and a le a f in itia l o r p r im o r d i u m . By thoroughly studying type of le a f growth and n u m b e r of l a t e r a l growing points which have been initiated one can b eco m e p r o f ic ie n t in d istinguishing flo r a l p r im o r d ia fr o m le a f p rim o rd ia. One o utstanding f e a tu r e found in th is study was the f i r s t flo w er p r im o r d iu m to be in itiated was found in th e axil of a much d w arfed le a f p r im o r d iu m . A fter s e v e r a l flow er p r im o r d ia w e re i n i ­ tia te d the le a v e s b e c a m e r u d im e n ta r y . B a s e d on th e se o b se rv a tio n s the u p p e r m o s t p r im o r d iu m on th e right side of the te r m in a l growing point in F ig u r e 20 w as la b e le d as a p ro b ab le flower p r im o r d iu m . In F ig u r e 21 is shown a developing young flo w e r. p r i m o r d i a w e r e c l e a r l y d is tin c t. Sepal Initiation of the o th er f lo r a l p a r t s had not o c c u r r e d . L a t e r a l Shoot Development In th e developm ent of a l a t e r a l shoot which m ay be e ith e r - 104 - F ig u r e 21. The growing point of a re p ro d u ctiv e cabbage plant h a r v e s te d M arch 27. po in t. x64 F ig u r e 22. bage. (a) Developing flower; (b) la t e r a l growing A developing l a t e r a l shoot p r im o rd iu m in cab (a) A l a t e r a l shoot p r im o r d iu m . x l2 8 - 105 - v e g e ta tiv e o r r e p r o d u c tiv e th e m e r i s t e m a t i c bud in the axil of a le a f b eg an to d if f e r e n t ia t e . As growth p ro c e e d e d the growing point of the l a t e r a l shoot a s s u m e d an a r c h i t e c t u r a l d esig n and g r o s s m orphology id e n tic a l with th a t in the growing point of the te r m in a l shoot. The tu n ic a in th e l a t e r a l shoot was fo rm e d by the two s u rfa c e cell l a y e r s in th e e a r l y sta g e s of grow th. Shown in F ig u r e 22 is a young l a t e r a l growing point in the leaf axil of a te r m in a l shoot. The tu n ic a was d is tin c t, and the co rp u s in itia ls w e re d etectab le but le s s d istin c t. The p la n e s of c e ll div isio n in the l a t e r a l growing point w e r e id e n tic a l with th o s e in the te r m in a l growing point. In the tu n ic a , cell d iv isio n s w e re a n ticlin al, the corpus in itials divided an tic lin a l and p e r i c l i n a l , and the cells in the rib m e r i s t e m divided in v a r io u s p la n e s . D ivisions w ere an ticlin al in the th ir d and fourth cell l a y e r s of th e p e r ip h e r a l zone except during the initiation of a l a t e r a l o r g a n when th e y w e re p e r ic lin a l . shown in F ig u r e 23. A young l a t e r a l shoot is The rib m e r i s t e m cells w e re in longitudinal ro w s which in d ic a te s th is l a t e r a l was in the rep ro d u c tiv e p h a s e . In F ig u r e 24 is a m o r e advanced stage in the growth of a l a t e r a l shoot. T his l a t e r a l shoot had a growing point m o rph o lo g ically c h a r a c t e r i s t i c of th e e a r l y s tag es of the re p ro d u ctiv e growth p h a s e . The l a t e r a l shoot shown in F ig u r e 25 was rap id ly initiating flo r a l p r i m o r d i a when it w as co lle c te d . - 106 - F ig u r e 23. A developing l a t e r a l shoot showing f i r s t p a ir of le a v e s in cab bag e, (a) P o r tio n of te r m in a l shoot; (b) old leaf; (c) young leaf; (d) la t e r a l growing point. F ig u r e 24. xl2 8 A developing la t e r a l shoot in cabbage. This l a t e r a l shoot is m o rp h o lo g ically c h a r a c t e r i s t i c of the e a rly s tag es of the r e p ro d u c tiv e growth p h a s e . xl28 - 107 - F ig u r e 25. A re p ro d u c tiv e l a t e r a l shoot in cabbage. xl28 a F ig u r e 26. F lo w e r in itiatio n in cabbage, (a) Corpus i n ­ itia ls ; (b) tu n ica la y e r; (c) flow er in itial in th ird and fourth cell l a y e r . x620 - 108 - F lo w e r D evelopm ent F l o r a l in itia ls a r o s e in th e u p p e r m o s t p a r t of th e p e r i p h e r a l zone of th e grow ing p o in t. The p r in c ip a l plan e of cell d iv isio n in th e th i r d and fo u rth cell l a y e r s of th is a r e a w as a n tic lin a l. When f lo r a l in itia ls w e r e being d if f e r e n tia te d a few of th e c e lls divided in a p e r i ­ clinal p la n e . E a r l y evidence of p e r ic lin a l cell div isio n in th e t h i r d and fo u rth cell l a y e r s is shown in F ig u r e 26. In F ig u r e 27 is shown a flow er bud in itia l r e s u ltin g f r o m p e r ic lin a l cell division f r o m the th i r d and fo u rth l a y e r s . It w as evident th a t th is was a flo ra l in itia l, b e c a u s e th e t e r m i n a l shoot f r o m which it was se le c te d was d e v e lo p ­ ing only f lo r a l i n i tia ls . Continued p e r ic lin a l and an ticlin al d iv isio n s of th e f lo r a l in itia ls r e s u l t e d in the fo rm a tio n of the flow er p r i m o r ­ d ium , F ig u r e 28, and th e young developing flo w er, F ig u r e 29. The o r d e r of a p p e a ra n c e of th e f lo r a l p a r t s , F ig u r e 30, 31 and 32, w as found to be s e p a ls , s ta m e n s , p is til and l a s t l y p e t a ls . A cross s e c ­ tio n of a flow er is shown in F ig u r e 33. It h a s b e e n g e n e r a lly in tim a te d in the l i t e r a t u r e that flow ering in c r u c i f e r e a is t e r m i n a l . In th is study, cabbage flo w ers w e re i n i ­ tia te d l a t e r a l l y on e ith e r side of the shoot apex in the sam e m a n n e r as le a v e s and l a t e r a l s h o o ts . F u r t h e r m o r e , the g r o s s shape and c e llu la r a p p e a ra n c e of the shoot apex in 3 re p ro d u c tiv e plant was not d iffe re n t f r o m that of a v e g etativ e p la n t. The growing points of the ygggj^g^yg and re p ro d u c tiv e p la n ts w e re d iffe re n t. To a tte s t the b e ­ lie f th a t th e a p ic e s of th e p la n ts in the two growth p h ase s w e re alik e, - 109 - F ig u r e 27. A developing flow er initial in cabbage, (a) P e r i c l i n a l cell d iv isio n s in the th ir d and fourth cell la y ers. x620 F ig u r e 28. b ag e. The developing flow er p r im o rd iu m in c a b ­ (a) F lo w e r p r im o r d iu m . xl2 8 - 110 - F ig u r e 29. The developm ent of a flow er showing sepal in itia ls in cabbage, pal i n i tia ls . (a) Advanced flower p rim o rd iu m ; (b) s e ­ x l2 8 F ig u r e 30. The developm ent of a flow er showing sepal p r im o r d iu m in cabbage, flow er p a r t to develop. (a) Sepal p rim o rd iu m , the f i r s t x l2 8 - Ill F ig u r e 31. - The developm ent of a flow er showing stam en p r im o r d iu m in cabbage, (a) Sepal; (b) stam en p r im o r d iu m . x l 28 F ig u r e 32. Longitudinal sectio n of a cabbage flo w er. (a) Sepal; (b) stam en; (c) p is ti l. The p etal, not shown is the la s t flow er p a r t to develop. x64 - 112 - F ig u r e 33. f lo r a l d ia g r a m , C r o s s sectio n of a cabbage flower showing (a) Sepal; (b) a n th er lobe, 2; (c) stam en; (d) p is ti l, 2 c a r p e ls ; (e) petal tip . F ig u r e 34. xlOO P h o to g rap h of a cabbage plant which was d e v e r n a liz e d by high t e m p e r a t u r e . After six weeks of t e m ­ p e r a t u r e s above 85° F . th is plant cea sed to flower and p r o ­ duced a s m a ll f ir m head at the su m m it of the seed stalk. - 113 - t e n r e p r o d u c tiv e p la n ts w e re d e v e r n a liz e d by subjecting th e m to t e m ­ p e r a t u r e s above 85° F # in th e g reen h o u se fo r six w eek s. As a r e ­ sult of th is t r e a t m e n t th e p la n ts c e a se d to flow er and w e re t r a n s ­ fo rm e d f r o m the re p r o d u c tiv e to the v eg etativ e growth p h a s e . The p lan t shown in F ig u r e 34 had seed pods on a Hseed stalk" which b o re a s m a ll but f i r m cabbage head at th e su m m it of the seed stalk . C e r ta in m o rp h o lo g ical changes which o c c u r as a plant t r a n s ­ f o r m s f r o m th e v eg e ta tiv e to the re p ro d u c tiv e phase have been d i s ­ c u s s e d ab ove. It should be noted th at the f i r s t evidence of in itiation of the r e p r o d u c tiv e growth p h a se w as about F e b r u a r y 24. A study of the shoots c o llected on th a t date f r o m the v a rio u s tr e a tm e n t s was th e n m a d e . E ffect of G row th-R egulating S ubstances Upon T im e of F lo w e r Initiation It w as found th a t th e m o rp h olo gical c h a r a c t e r i s t i c s of the growing p o in ts w ithin a tr e a t m e n t w ere s im i la r but g re a t d iffe re n c e s among the v a r io u s tr e a t m e n t s w e re o b s e rv e d . Seed stalk initiation had o c c u r r e d in c e r t a in tr e a t m e n t s on F e b r u a r y 24 while in o th e r tr e a t m e n t s it had n o t. P la n t s iz e at the tim e of cold-induction had no effect upon the tim e of in itia tio n in re p ro d u c tiv e p la n ts . Initiation o c c u r r e d in m e ­ d iu m s iz e p la n ts as e a r l y as in la r g e p la n ts . The growing points of the s m a ll p la n ts w e r e v eg etativ e and consequently no seed s ta lk in i- - 114 - tia tio n o c c u r r e d . L a r g e P la n ts T h e r e w as li ttl e evidence on F e b r u a r y 24 to indicate th at i n i ­ tia tio n of th e re p r o d u c tiv e growth p h ase had o c c u r r e d in any of the la r g e c o n tro l p la n ts . not e n la r g in g . L a t e r a l growing points in the axils of the le a v e s w e re The only ind icatio n was th e c ells in the rib m e r i s t e m ju s t b en eath th e co rp u s in itia ls w e r e being fo rm ed in longitudinal ro w s, F ig u r e 35. F ig u r e 36 r e p r e s e n t s a growing point collected F e b r u a r y 24 f r o m a p lant s p ra y e d with C1PP b e fo re induction. The rep ro d u ctiv e p h ase h ad b een in itia te d in th e growing points of all p lan ts exam ined fo r th is t r e a t m e n t . C ells in th e rib m e r i s t e m w ere in longitudinal ro w s , and l a t e r a l growing points w e re d ifferen tiatin g throughout the length of th e shoot. No evidence of in itia tio n ex isted on F e b r u a r y 24 in any of the p la n ts s p ra y e d d u rin g induction with C1PP, F ig u r e 37. The cells in th e r ib m e r i s t e m w e r e not a r r a n g e d in longitudinal rows but in a nond e s c r ip t iv e m a n n e r . No l a t e r a l growing points w ere differentiating in any p la n ts ex a m in e d . seen* In F ig u r e 38, evidence of initiation can be T his fig u re is r e p r e s e n ta tiv e of th e la rg e plants on F e b r u a r y 24 which w e r e s p ra y e d a f te r induction with C1PP. B a s e d on th is study th e o r d e r of initiation among the la r g e p lants s p ra y e d at v a r io u s t i m e s with C1PP follows: f i r s t , in plants sp ra y ed b e fo re induction; second, in p lan ts sp ra y e d a fte r induction; th i r d , in - 115 - F ig u r e 35. The growing point of a cabbage plant (larg e size) h a r v e s te d F e b r u a r y 24. the re p ro d u c tiv e p h a s e . T h e re is little evidence of x64 ■ ■ F ig u r e 36. v k The growing point of a cabbage plant (larg e size) s p ra y e d with C1PP b efo re cold-induction and h a rv e s te d F e b r u a r y 24. (a) Rib m e r i s t e m c e lls form ing in longitudinal row s and (b) l a t e r a l growing points developing in the le af axils a r e indicative of the re p ro d u c tiv e p h a se . x64 - 116 - F ig u r e 37 . The growing point of a cabbage plant (larg e szie) s p ra y e d with C1PP during cold-induction and h a rv e s te d F e b r u a r y 24. T h e r e is no evidence of the rep ro d u ctiv e p h a s e . x64 # F ig u r e 38. The growing point of a cabbage plant (larg e size) s p ra y e d with C1PP a f te r cold-induction and h a rv e s te d F e b r u a r y 24. The rib m e r i s t e m cells w ere form ing in lo n g i­ tudinal row s and a few l a t e r a l growing points w ere developing when th is t e r m i n a l shoot was h a r v e s te d . x64 - 117 - c o n tro l p la n ts ; and fo u rth , in p la n ts s p ra y e d during induction. P h o to m ic r o g r a p h s of th e growing points of la r g e p la nts s p ra y e d with 2 ,4 - D b e f o r e , d u rin g and a f te r th e induction tr e a tm e n t a r e p r e ­ se n ted in F i g u r e s 39, 40 and 41, r e s p e c tiv e ly . T h e s e shoots showed li ttl e in d ic a tio n th a t th e re p ro d u c tiv e p h a se had been in itia ted when the shoots w e r e c o lle c te d on F e b r u a r y 24. Studies m ade of shoots co llected two w eeks l a t e r in d ic a te d th a t in itia tio n o c c u r r e d e a r l i e s t in p lants sp ray ed b e f o r e induction and l a t e s t in plants sp ra y e d during induction. The d iffe re n c e in ti m e of in itia tio n betw een the p lants sp ra y e d b efo re and th o s e s p ra y e d a f te r induction was neg lig ib le. P la n ts sp ray ed during co ld -in d u ctio n w e re c o n s id e ra b ly le s s advanced in the r e p r o ­ ductive p h a s e th a n p la n ts sp ra y e d b efo re o r a fte r induction. M edium P la n ts In the co n tro l p lan ts of m edium size c e r ta in m orphological ch an g es, a s s o c ia te d with th e in itia tio n of the rep ro d u ctiv e growth p h a s e , w e r e noticed in t e r m i n a l shoots collected F e b r u a r y 24. Cells in the rib m e r i s t e m w e r e beginning to f o r m longitudinal rows and l a t e r a l growing point p r i m o r d i a w e re d ifferen tiatin g in the axils of the leaf p r i m o r d i a , F ig u r e 4 2. A c o m p a ris o n of th e te r m in a l growing point shown in F ig u r e 42 with the one in F ig u r e 43 shows that initiation of the re p r o d u c tiv e p h a se was slightly m o r e advanced in plants sp ray ed With C1PP b e f o r e induction th a n in the control p la n ts . L a t e r a l growing points w e r e growing in th e a x ils of the o ld e r le av es of plants sp ray ed 118 - F ig u r e 39. The growing point of a cabbage plant (la rg e size) sp ra y e d with 2 ,4 -D b efo re co ld-induction. Rib m e r i ­ s te m c e lls w e re fo rm in g in longitudinal rows when h a r v e s te d F e b r u a r y 24. F ig u r e 40. x64 The growing point of a cabbage plant (larg e size) s p ra y e d with 2 ,4 - D during cold-induction. A few l a t e r a l growing points w ere developing when h a rv e s te d F e b r u a r y 24. x64 - 119 - F ig u r e 41. The growing point of a cabbage plant (larg e size) s p ra y e d with 2 ,4 - D a fte r cold-induction. A few la t e r a l growing points w e re developing and the rib m e r i s te m cells w e re fo rm in g in longitudinal rows when h a rv e s te d F e b r u a r y 24. x64 F ig u r e 42. The growing point of a cabbage plant (medium size) in the c o n tro l. L a t e r a l growing points w ere beginning to develop and rib m e r i s t e m c e lls w ere forming in longitudinal row s when h a r v e s te d F e b r u a r y 24. L x64 - 120 - F ig u r e 43. The growing point of a cabbage plant (m edium size) s p ra y e d with C1PP b efo re cold-induction. L a t e r a l g ro w ­ ing points w e re developing and rib m e r i s t e m cells w ere form ing in longitudinal row s when h a r v e s te d F e b r u a r y 24. F ig u r e 44. x64 The growing point of a cabbage plant sprayed with C1PP d u rin g co ld -in d u ctio n . G en eral d iso rg an izatio n of th e c e lls o c c u r r e d in all shoots h a r v e s te d F e b r u a r y 24 from th is t r e a t m e n t but no evidence of initiation of the reprod u ctiv e p h ase was o b s e r v e d . x64 - 121 - b e f o r e induction. No evidence of in itia tio n w as found in any te r m in a l shoots ex am in ed of p la n ts s p ra y e d durin g induction, F ig u r e 44. A g e n eral la c k of o r g a n iz a tio n of th e c e lls was o b s e rv e d e sp ecially in the apices of a ll shoots c o llected F e b r u a r y 24 f r o m plants s p ray ed during in d u c­ tio n with C 1 P P , F ig u r e 44. Shoots collected fro m all tr e a tm e n t s w ere s i m i l a r l y handled throughout th e h isto lo g ical p ro c e d u re for any one sam p lin g d a te . T h o se h a r v e s te d on different dates w ere handled as n e a r l y alik e a s p o s s i b le . One might a s s u m e th at C1PP applied during induction i n t e r f e r e s with n o r m a l c e llu la r o rg an ization during the p e r io d of in itia tio n . As will be pointed out l a t e r such pronounced d i s ­ o rg a n iz a tio n of the c e lls was not o b se rv e d in shoot apices h a rv e s te d f r o m any t r e a t m e n t s b e fo re o r a f te r F e b r u a r y 24. A s im i la r but le s s pro n o u n ced r e s p o n s e w as o b s e rv e d in the ap ices of te r m in a l shoots c o l­ le c te d F e b r u a r y 24 of p lan ts sp ra y e d a fte r the induction t r e a tm e n t , F ig u r e 45. L a t e r a l growing points w e re differentiating in th e s e t e r ­ m in al shoots which in d ic a te s in itiatio n of the rep ro d u ctiv e p h a s e . In itiatio n of the r e p ro d u c tiv e growth ph ase ap peared to have o c c u r r e d e a r l i e s t in th e p lan ts sp ray ed before induction. The plants in the c o n tro l w e r e next in o r d e r followed by those sp ray ed a fte r in d u c­ tio n . T e r m in a l shoots of m ed iu m size plants sprayed with 2 ,4 -D b e ­ f o r e , d u rin g and a f te r the induction tr e a tm e n t a r e shown in F ig u r e s 46, 47 and 48, r e s p e c t iv e ly . Initiatio n of the rep ro d u ctiv e phase was m o re - 122 F ig u r e 45. The growing point of a cabbage plant (m edium size) s p ra y e d with C1PP a f te r co ld -in d u ctio n . T h e r e was slight c e l lu la r d is o r g a n iz a tio n in the shoots h a r v e s te d F e b r u a r y 24 f r o m th is t r e a t m e n t and slight evidence of in itia tio n of the r e ­ p ro d u c tiv e p h a s e . Figure 46. x64 T h e g r o w i n g point of a c a b b a g e plan t ( m e d i u m s i z e ) s p r a y e d w it h 2 , 4 - D b e f o r e c o l d - i n d u c t i o n . February 24. x64 H arvested - 123 - F ig u r e 4 7 . The growing point of a cabbage plant (m ed iu m size) s p ra y e d with 2 ,4 - D durin g co ld -in d u ctio n . H a r v e s te d F e b r u a r y 24. Figure 48. x64 T h e g r o w i n g point of a c a b b a g e plant ( m e d i u m s i z e ) s p r a y e d w ith 2 , 4 - D a f t e r c o l d - i n d u c t i o n . H arvested February 24. x64 - 124 - ad v an c ed in p la n ts s p ra y e d b e f o r e ( F ig u r e 46) and a f te r th e induction t r e a t m e n t ( F i g u r e 48) th a n in th e co n tro l ( F ig u r e 42). T h e r e was no o b s e r v a b le d if f e r e n c e b etw een p la n ts s p ra y e d b e fo re and th o s e s p ra y e d a f t e r th e induction t r e a t m e n t . P la n ts s p ra y e d with 2 ,4 -D durin g i n ­ d u ction showed a lm o s t no evidence of in itia tio n on F e b r u a r y 24. A study of th e shoots h a r v e s te d two w eeks l a t e r r e v e a le d th a t in itiation had o c c u r r e d . T h e s e m o rp h o lo g ic a l o b s e rv a tio n s h a rd ly c o r r o b o r a te th e d ata in T ab le 16 dealin g with the growth p h ase index. These in ­ c o n s is te n c ie s m a y be a ttr ib u te d to v a r ia tio n in auxin content of the two groups of p la n ts at o r im m e d ia te ly following in itia tio n . S m all P la n ts T h e r e w e r e no in d icatio n s of in itiatio n of the re p ro d u c tiv e p h a s e in any of the s m a ll p la n ts ex am in ed . S e a s o n a l Changes in the T e r m in a l Growing P o in ts of P la n ts Kept V eg etativ e by G row th-R egulating S ubstances L ittle change o c c u r r e d during th e s easo n in the g e n e ra l m o r p h o l­ ogy of th e growing p oints of p la n ts sp ra y e d with C1PP during the in d u c ­ tio n t r e a t m e n t . The g e n e ra l m orphology of such plants is shown in F i g u r e s 49, 50 and 51. S p ecim en s used in p r e p a r in g th e s e p h o to ­ m i c r o g r a p h s w e r e co llected J a n u a ry 20, k la rc h 27 and A pril 14, r e ­ s p e c tiv e ly . It is to be r e c a lle d fr o m the p reced in g d is c u s s io n how ever th a t on F e b r u a r y 24, the tim e of seed s ta lk initiation, m a rk e d c e llu la r d is o r g a n iz a tio n o c c u r r e d in the growing points of the p lan ts in th is t r e a t - - 125 - F ig u r e 49. The growing point of a cabbage plant (m edium size) s p ra y e d with C1PP during cold-induction. J a n u a r y 20, 1950. H a rv e ste d x64 llsS F ig u re 50. The g r o w i n g point of a ca bb age plant ( m e d i u m s i z e ) s p r a y e d w it h C1PP d u rin g c o l d - i n d u c t i o n . M a r c h 2 7, 1 9 5 0 . x64 H arvested - 126 - F ig u r e 51. The growing point of a cabbage plant (m edium size) s p ra y e d with C1PP during cold-induction. A pril 14, 1950. f x64 H a rv e s te d - 127 - m e n t. Such, d is o r g a n iz a tio n did not p r e v a il two weeks p r i o r o r two w eeks su b se q u en t to F e b r u a r y 24. In F ig u r e 49, in d ic atio n s a r e th a t a few of the c e lls in th e rib m e r i s t e m re g io n had f o r m e d in longitudinal r o w s . T e r m in a l shoots c o lle c te d M a r c h 27, F ig u r e 50, a p p e a re d to be slightly elongated as c o m p a r e d w ith genuinely v eg etativ e s h o o ts . Even so, th is shoot could not b e c l a s s i f i e d as being in th e re p ro d u c tiv e p h a s e . The shoot r e p r e ­ s e n te d in F ig u r e 51 w as s t r i c t l y v eg etativ e and is c h a r a c t e r i s t i c of o th e r s c o lle c te d A p ril 14 f r o m plan ts s p ra y e d during cold-induction with 250 ppm C1PF. - 128 - DISCUSSION R e s u lts of th is study su p p o rt th e findings of B osw ell (7) and M ill e r (59) th a t low t e m p e r a t u r e is th e m a in en v iro n m en tal f a c to r a s ­ s o c ia te d w ith p r e c o c io u s seeding in cab b ag e. In addition, the size of th e p la n ts when su b je c te d to low t e m p e r a t u r e s is an im p o rta n t fa c to r (7) and (48). L a r g e p la n ts have g r e a t e r te n d en cies to shoot to seed th a n s m a ll o n e s . P la n t s with s te m d i a m e t e r s 6 m m . o r l a r g e r at c o l d - t r e a t ­ m e n t of a p p ro x im a te ly 38° F . fo r 42 days bolted, w h ereas pla nts with d i a m e t e r s of 4 m m . did not b o lt. T h e r e was c o n s id e ra b le d iffe re n c e in re s p o n s e by the two v a r i ­ e tie s to co ld -in d u ctio n t r e a t m e n t . Golden A cre plants having a s te m d i a m e t e r of 6 m m . o r g r e a t e r r e a d ily bolted a f te r cold-induction. Round Dutch p la n ts with s te m d ia m e te r s of 6 to 7 m m . did not bolt a f te r a s i m i l a r cold t r e a t m e n t . Although t e m p e r a tu r e had a pronounced effect on p r e m a t u r e flow ering in cabbage, th is effect was influenced in both v a r i e t i e s by g ro w th -re g u la tin g s u b s ta n c e s . T h ese su b sta n c e s alone did not have sufficient influence to change the growth p h ase fr o m v e g e ta tiv e to r e p r o d u c tiv e , but a p p e a re d to aid such changes when u sed in co m b in atio n with th e en v iro n m en t. The influence of the su b sta n c e s applied v a r ie d with the c h e m ic a ls , c o n c e n tr a tio n s , plant s iz e s and tim e s of ap p licatio n . Aside from, f o r m ­ a tiv e effects and i n c r e a s e d growth r a t e during th e seedling stage th e m o s t o u tsta nd in g c h e m ic a l in flu en ces w e r e noticed in p lan ts t r e a t e d with 2 ,4 - D , - 129 - C1PP and M H. V eg etativ e grow th r a t e was s tim u la te d in young p lan ts soon a f t e r t r e a t m e n t with low co n c e n tra tio n s of NA, but th is r e s p o n s e w as not n o tic a b le a few w eeks a f te r t r e a t m e n t . Application of TIB A as u s e d in t h e s e e x p e r im e n ts had no a p p a re n t effect on plant grow th. R ece n t concepts co ncern in g m e c h a n is m s involved in the t r a n s ­ itio n of p la n ts f r o m the v e g e ta tiv e to the re p ro d u c tiv e p h ase c e n te r aro u n d th e h y p o th e sis of existing flo w er-in d u cing and flo w er-inh ibiting su b stan ces* Cailadbjan ( 9 ) su g g ested th a t a h o rm o n al su b stance which he c a lle d ’’f lo r i g e n ” was p ro d u ced in th e le a v e s and tr a n s l o c a te d to the growing p o in t. A ccording to th e th e o ry sufficient q uantities of the s u b ­ s ta n c e m u s t r e m a i n in th e growing point fo r sufficient tim e for flow er induction to o c c u r . Cholodny (10, 11) m ade a d ifferen t ap p ro ach by su g g estin g th a t f lo r ig e n m ight be an o r d in a r y auxin o r aux in -lik e s u b ­ s ta n c e and not a sp ecific flow er inducing s u b sta n c e . Lang (51), in d is c u s s in g th e physiology of flowering in long and s h o r t d ay p la n ts , v is u a liz e d two b a s ic a lly d ifferen t p o s s ib ilitie s : 1 , an ind u ctiv e day length which p ro m o te s flow ering and 2 , a non-inductive day length which inhibits flo w erin g . The f o r m e r im p lies that p la n ts a r e not cap ab le of flow ering u n le s s photo-induced so as to build up a f lo w e r ­ ing s tim u lu s . The l a t t e r im p lie s th a t p lan ts a r e capable of flow ering but flo w erin g is s u p p r e s s e d by non-inductive day lengths which builds up a flo w erin g in h ib ito r . F r o m th e s e p o s s ib ilitie s Lang concludes th a t f lo r a l in itia tio n , in long day and s h o rt day p la n ts , is d e te r m in e d by flo w erin g s tim u li g e n e ra te d in the le a v e s and tr a n s l o c a te d to the growing - 130 - p o in t* H e fu r th e r c o n c lu d e s fr o m r e s u lt s o f g r a ftin g e x p e r im e n ts w ith lo n g and s h o r t d a y p la n ts th a t th e f lo w e r in g s tim u li of th e tw o p la n ts a r e s i m i l a r and p o s s i b l y th e sa m e* D e f in it e p r o o f h a s not b e e n e s t a b lis h e d , a s p o in te d out b y L a n g , th a t s u b s ta n c e s e x tr a c te d f r o m flo w e r in g p la n ts and in tr o d u c e d in to n o n -f lo w e r in g p la n ts c a u s e d f lo r a l in itia t io n . P la n t s w hich r e q u i r e th e rm o -p h o to in d u c tio n build up two f lo r a l s tim u li a c c o rd in g to L ang (51)* The stim u lu s produced during th e cold t r e a t m e n t h a s b e e n c a lle d " v e r n a lin 11 and c o n sid e re d to be a p r e c u r s o r w hich a c ts as a c a ta ly s t of flo rig e n fo rm a tio n . c o u r s e of v e r n a liz a tio n was auto c a ta ly tic . P u r v is ( 6 8 ) b elieved the This could well be and if t r u e e x p lain s why th e stim u lu s cannot be e x tra c te d fr o m living c e l ls . T he s e v e r a l h y p o th e ses and p o s s ib ilitie s set fo rth by Lang (51) can be explained on th e b a s is of s y n th e s is , le v e l, economy and d is trib u tio n of auxins o r ph y to h o rm o n es Many a u th o rs have p r e f e r r e d to explain t h e i r r e s u l t s w ith the phytohorm one th e o ry (4, 5, 6 , 11, 14, 15, 25, 36, ip., 5 2 ,5 5 ,5 7 ,9 2 ,9 3 ,9 4 ,9 5 ). The r e c e n t w ork of Leopold and a s s o c ia te s ( 5 2 ,5 3 ,5 5 ,5 7 ) have r a t h e r conclusively shown that auxins e x e r t an e f ­ fect on flow ering in W inter b a r le y , A laska p ea, B iloxi soybean and W in ter r y e . D ata have b een r e p o r te d (14) to indicate th at phytohorm one c o n ­ te n t f lu c tu a te s in c e l e r y during and subsequent to cold-induction t r e a t ­ m e n t. A low phytohorm one le v e l during induction followed by an 1 See T e rm in o lo g y , page 24. -131- i n c r e a s e su b seq u en t to induction a p p e a rs to be a s s o c ia te d with se e d s ta lk in itia tio n ( 1 4 ,5 1 ) . G u stafso n (36) p r e s e n te d data which show a re d u c tio n in p h y to h o rm o n e s in p la n ts grown at te m p e r a t u r e s above 30° C. B ran d is and M cQ u ire ( 8 ) hav e shown th a t heat (52^ C. for 20 m inutes) d e s tr o y s th e g e o tro p ic r e s p o n s e in c ro p s with i n t e r c a l a r y m e r i s t e m s such as sugar cane. T h is r e s p o n s e was r e s t o r e d by soaking th e p lants in a s o lu ­ tio n containing 100 m g . / I of in d o leacetic acid . T h e ir data stro n g ly s u g ­ g e s t th a t low t e m p e r a t u r e had a s im i la r effect which in d icates t h e r e a r e m in im a l, o p tim al and m a x im a l t e m p e r a t u r e ran g es fo r auxins and p h y to h o r m o n e s . Leopold (57) p r e s e n te d data which conclusively show an in te r a c ti o n of auxin and t e m p e r a t u r e in flow er in itiatio n . He found a d if f e r e n tia l r e s p o n s e to auxin applied to long day, sh o rt day and i n ­ d e t e r m in a t e p la n ts which w e re grown under v a rio u s t e m p e r a t u r e s . Auxin (NA) t r e a t e d p la n ts su b seq u en tly grown u n d er low t e m p e r a tu r e conditions flo w e re d e a r l i e r and m o r e p ro fu s e ly th a n the c o n tro ls . Under a v e ra g e t e m p e r a t u r e s (1 8 -2 0 ° C .) applied auxin had no effect o r inhibited f lo w e r ­ ing depending on th e p la n t. Van O v e rb e e k et j d ( 9 4 ) found th a t the s te m ap ices of pineapple p la n ts contained la r g e q u an tities of f r e e phytohorm one (called f r e e auxin by V an O verbeek) but s m a ll am ounts of bound phytohorm one (bound auxin); w h e r e a s , th e le a f b a s is contained little f r e e and la r g e q uan tities of bound p h y to h o rm o n e . Skoog (80) c o n s id e re d cabbage le a v e s to contain r e la tiv e ly l a r g e am o u n ts of bound phytohorm one, o r 4 m g. p e r k g . f r e s h w eight. Van O v e rb e e k et al (94) a s s u m e d the tr a n s f o r m a tio n of bound phytohorm one - 132 - to f r e e ph y to h o rm o n e to c au se flow ering in p ine ap p le. Low t e m p e r a ­ t u r e s m a y r e d u c e th e f r e e o r activ e phytohorm one content in the apex, c a u s e a change of phytohorm one d is tr ib u tio n in p lants o r modify the p b y to h o rm o n e m e c h a n is m so as to r e l e a s e the bound phytohorm one in th e l e a v e s . T h is h y p o th e sis ta k e s into account th e function of th e le a v e s and s te m tip s in f lo r a l in itia tio n . It finds support in e x p e rim e n ta l e v i­ dence with pin eapp le (94); c e l e r y (14,21); and b a r le y , soybean, p ea, and r y e (57) • R e s u lts r e p o r te d h e r e with r e s p e c t to cabbage ap p ea r to be r e a d i ly explained by th e auxin o r p r e f e r a b ly phytohorm one th e o ry . With th is t h e o r y it b e c o m e s n e c e s s a r y to m ake c e r ta in a s s u m p tio n s. t e m p e r a t u r e a l t e r s th e phytohorm one m e c h a n is m . F irst, Such an a s s u m p tio n is f e a s ib le sin ce an in te r a c tio n betw een te m p e r a tu r e and auxin and t e m ­ p e r a t u r e and p h y to h o rm o n es have been d e m o n stra te d e x p e rim e n ta lly ( 1 4 ,2 1 ,5 7 ) . Second, low t e m p e r a t u r e s (below 45° F . ) and high t e m ­ p e r a t u r e s (85° F . and above)tendto low er the f r e e phytohorm one lev el (8 , 14, 21). T h ir d , v eg etativ e growth is favored by a s ta tic phytohorm one supply, and re p ro d u c tiv e growth is fav o red by a r a t h e r high p h y to h o r­ m one supply following a r a t h e r low one ( 1 4 ,2 1 ,9 4 ) . Along with th e s e a s s u m p ti o n s , c e r t a i n g e n e ra liz a tio n s can be m a d e. F i r s t , cabbage p la n ts held at t e m p e r a t u r e s of 50° to 80° F . re m a in v eg etativ e p o s sib ly a s a r e s u l t of an econom ic u se of a s ta tic phytohorm one supply. Second, p la n ts held below 45° F . for sufficient tim e tend to bolt as a r e s u lt of a r e d u c tio n of f r e e phytohorm one in the apex followed by a sh a rp - 133 - i n c r e a s e b ro u g h t about by a r e l e a s e of the bound fo r m in the le a v e s . T h i r d , th e r e a s o n l a r g e cabbage p lan ts bolt m o r e re a d ily th a n s m a ll ones m ig h t b e elu cid a ted by the p o s s ib ility of a g r e a t e r supply of bound p b y to h o rm o n e ex istin g in l a r g e p la n ts th a n in s m a ll. Such a thought is c o r r o b o r a t e d by th e fact th a t t e m p e r a t u r e s below 45® F . for two to fo u r w eek s change th e grow th c h a r a c t e r in s m a ll plants ( 7 ), although such t r e a t m e n t s a r e in su fficien t to induce the rep ro d u ctiv e p h a s e . F o u r t h , d if f e r e n c e s in bolting te n d en cies among v a r ie tie s m ay be i n ­ t e r p r e t e d on th e b a s is of a g r e a t e r phytohorm one stab ility existing in slow bolting v a r i e t i e s , such as Round Dutch, th a n in v a r ie tie s which bolt r e a d i ly , such as Golden A c r e . The bound phytohorm one might be r e l e a s e d to th e f r e e f o r m f a s t e r in Golden A cre than in Round D utch . (14). Such is th e c a s e in bolting and slow bolting c e le r y v a r ie tie s If t r u e with cabbage it explains why c e r ta in v a r ie tie s r e q u ir e lo n g e r cold t r e a t m e n t s th a n o th e rs to induce th e rep ro d u ctiv e p h a s e . T he d e v e r n a liz a tio n r e s p o n s e brought about in cabbage as m e n tio n ed above by high t e m p e r a t u r e s m ay well be explained on the b a s i s of a lo w erin g of th e phytohorm one content by the high t e m p e r a ­ tu re s. Growth c h a r a c t e r i s t i c s of d e v e rn a liz e d plants w e re a lm o st id e n tic a l w ith p la n ts t r e a t e d with MH, which indicates th at MH m ay be an a n ti-p h y to h o rm o n e as well as an an ti-au x in as d e m o n s tra te d by L eopold and K lein (54). An h y p o th e sis is p r e s e n te d above with r e f e r e n c e to a p o s sib le r o le p la y ed by p h y to h o rm o n es in the t r a n s f o r m a tio n f r o m the v e g e ta tiv e - 134 - to r e p r o d u c t iv e grow th p h a s e in cabbage. The question a r i s e s as to the r o le of s y n th e tic g r o w th -re g u la tin g su b sta n c e s when applied to v a r io u s p la n t s i z e s at v a r i e d t i m e s with r e s p e c t to cold -in d u ctio n. A pparently 2 ,4 - D e x e r t e d an influence upon the phytohorm one m e c h a n is m which te n d ed to s ta b iliz e th e f r e e phytohorm one supply, ir r e s p e c t iv e of th e t i m e it w as ap p lie d . sm all p la n ts. R e sp o n se s w e re s i m i l a r in la r g e , m edium , and T he d e g r e e of e ffe c tiv e n e s s , how ever, was g r e a t e r in s m a ll and m e d iu m th a n in l a r g e p la n ts . T h ese d iffe re n c e s might be e x ­ p la in e d on th e b a s i s of a g r e a t e r to ta l quantity of bound phytohorm one in l a r g e p la n ts th a n in s m a l l e r o n e s . P o s s ib ly 2 ,4 -D was m o r e stab le th a n th e p h y to h o rm o n es to low t e m p e r a t u r e s . R e s p o n s e to C1PP v a r ie d c o n siste n tly with tim e of ap p licatio n . F lo w e rin g a p p e a re d to be s tim u la te d when th is substance was applied b e f o r e o r a f te r th e cold -in d u ctio n t r e a t m e n t . In sh arp c o n tra s t, flo w erin g w as inhibited o r s u p p r e s s e d when C1PP was applied during c o ld -in d u c tio n . The outstanding r e s p o n s e fr o m th is ch em ical was o b tain ed when p lan ts w e re m ed iu m s iz e . P la n ts tr e a te d b efo re o r a f t e r co ld -in d u ctio n flo w ered e a r l i e r and m o re p ro fu se ly than the co n ­ tro ls. T h o se t r e a t e d durin g th e induction tr e a tm e n t did not flo w er, and only 4 out of 20 p la n ts te n d ed to develop seed s ta lk s . T h e r e a p p e a rs to be no c l e a r , a ll- e n c o m p a s s in g explanation of th e s e r e s u l t s . It might be a s s u m e d th a t low t e m p e r a t u r e s g rad u ally low er the f r e e phytohorm one c o n te n t. A p p aren tly it is n e c e s s a r y fo r the r e la tiv e le v e l of f r e e phyto- h o rm o n e to d ro p r a t h e r low, o r to fluctuate widely b efo re the re p ro d u c tiv e - 135 - p h a s e i s in d uced . If such is th e c a s e , p la n ts sp ra y e d with C1PP b e fo re induction had a n o r m a l phytohorm one content and a high au x in -lik e c h e m ic a l content at the beginning of the cold s to ra g e t r e a t m e n t . As a r e s u l t of low t e m p e r a t u r e th e r e la tiv e le v e ls of th e s e ch em ic als w e re r e d u c e d , followed by a s h a rp i n c r e a s e a f te r the cold-induction t r e a t ­ m e n t. The r e s u l t s su g g est th a t w ithin c e r t a in lim its the ran g e o v er w hich t h e s e s u b s ta n c e s flu ctu ates m ay be a m o r e d ecisiv e fa c to r than th e a c tu a l q u an tity at any given le v e l. L ack of seed stalk developm ent and su b se q u en t flow ering in m ed iu m s iz e p lan ts sp ray ed during the c o ld -in d u c tio n t r e a t m e n t m a y be s im i la r l y explained. The r e la tiv e le v e l of f r e e phytohorm one at the beginning of induction was biologically th e s a m e a s in p lan ts s p ra y e d b e fo re induction. No ch em ical was a p ­ plied h o w ev er to r a i s e th e r e la tiv e auxin le v el as with p lan ts sp ray ed b e f o r e induction. D uring th e f i r s t 21 days of cold-induction tr e a tm e n t low t e m p e r a t u r e s did not re d u c e th e f r e e phytohorm one to a le vel s u f ­ f ic ie n tly low to induce th e re p ro d u c tiv e p h a se , o r did not effect adequate r e l e a s e of th e bound f o r m . At th e end of 21 days m o r e au x in -lik e c h e m ic a l (C1PP), w as applied which m a y have r a is e d the le v el of a u x in -lik e s u b s ta n c e s in the p la n ts . This substance (C1PP) in som e way s e r v e d at l e a s t som e of the sam e functions as phytohorm one. Then th e re m a in in g 21 days of co ld-induction t r e a tm e n t w e re insufficient to e ffe c tiv e ly r e d u c e th e s e su b stan ces low enough to induce th e re p ro d u c tiv e grow th p h a s e . A nother p o s s ib ility is the application of C1PP during co ld - induction p r e v e n te d th e wide fluctuation in phytohorm one content - 136 - n e c e s s a r y to induce re p ro d u c tiv e d ev elo p m en t. The stim u lativ e r e s p o n s e f r o m C1PP ap p lied a f te r induction can t h e r e f o r e be explained on the b a s is of a low le v e l of f r e e phytohorm one r e s u ltin g fro m the low t e m p e r a t u r e t r e a t m e n t followed by an e x tr e m e ly high le v el of auxin brought about by th e ap p lic a tio n of C 1 P P , and th e r e l e a s e of bound phytohorm one. T his high auxin le v e l following cold -in d uctio n stim u lated growth and r e p r o d u c ­ tiv e d e v e lo p m e n t. The phyto h o rm o n e th e o ry is also applicable to the r e s u l t s o b ­ ta in e d with MH applied to m e d iu m size p lan ts at v a r ie d tim e s with r e ­ sp ect to the co ld -in d u ctio n t r e a t m e n t . Definite evidence has been p r e ­ sen ted th a t MH is an a n ti-a u x in (53,54) and th is ch em ical might t h e r e ­ f o r e be u s e fu l in red u cin g th e f r e e phytohorm one le v e l. h e r e le n d s evidence to such a p o s s ib ility . D ata r e p o r te d Round Dutch p lants sp ray ed b e f o r e a p a r t i a l co ld -in d u ctio n tr e a tm e n t developed m o re open heads th a n th e c o n t r o l s . Although th e s e p lan ts produced m o re open heads no s e e d s ta lk s o r flo w e rs a p p e a r e d . Such re s p o n s e m ay be in te r p r e te d as m e an in g th a t MH re d u c e d th e f r e e phytohorm one supply in the apex. In view of th e fact th a t c o m p a ra tiv e ly little growth o c c u r r e d in the MH t r e a t e d p la n ts it s e e m s lik ely th a t MH a l te r e d th e e n tire phytohorm one s y s t e m to th e extent th a t bound phytohorm one in the le a v e s was not r e ­ l e a s e d to the f r e e f o r m , and tr a n s lo c a te d to the apex so as to effect g ro w th . All p la n ts s p ra y e d with MH during cold- induction pro duced open h e a d s , and about h alf of th e m developed elongated s te m s and le a v e s m o rp h o lo g ic a lly c h a r a c t e r i s t i c of re p ro d u c tiv e p la n ts . The la ck of - 137 - flo w erin g r e s p o n s e in th is tr e a t m e n t was due p o ssib ly to the sam e r e a s o n a s th o s e s p ra y e d b e f o r e induction. The te r m in a l bud was killed in m o s t p la n ts s p r a y e d a f te r co ld -in d u ctio n . The r e a s o n for the le th a l r e s p o n s e o btain ed is b eliev ed to be due to the h ig h e r t e m p e r a t u r e s e n ­ d u r e d following c h e m ic a l t r e a tm e n t by th e s e p lan ts th an by th o s e sp ra y e d b e f o r e o r d u rin g induction. P la n ts s p ray ed b efo re and during the cold t r e a t m e n t w e r e su b je c te d to a p p ro x im a te ly 38° F . following s p ra y a p ­ p l i c a ti o n s . T h o se s p ra y e d a f te r cold-induction w e re moved im m e d ia te ly to a g re e n h o u s e w h e re th e a v e r a g e t e m p e r a t u r e was above 65° F . M ore of th e a c tiv e MH c h e m ic a l was pro b ab ly a b so rb e d by the p lants at th is h ig h e r t e m p e r a t u r e , r e s u ltin g in s e v e r e stunting o r killing of the t e r ­ m in a l b u d s . Had MH s p ra y e d p lan ts been subsequently tr e a te d with an auxin o r a u x in -lik e su b stan ce the r e s u l t s might have been v e r y d iffe re n t. K lein and Leopold (45) su g g est th at MH has no d ir e c t influence on f lo w e r ­ ing but a l t e r s th e auxin m e c h a n is m which subsequently affects f lo w e r ­ ing. R e s u lts of th e s e e x p e rim e n ts indicate th a t MH a l t e r s th e phyto- h o r m o n e s y s t e m which subsequently affects flow ering. With r e s p e c t to the m o rp h o lo g ical studies it will be r e c a lle d th at l a r g e p la n ts had c o rre s p o n d in g ly l a r g e r growing points th a n m ed iu m o r s m a ll o n e s . Too, only slight changes o c c u r r e d in the growing points w hile the p la n ts w e r e being cold t r e a t e d . Then, a f te r growth s t a r t e d in s p rin g t h e r e w e r e no m a jo r g r o s s changes in th e t e r m i n a l growing p o in ts of p la n ts m aking v eg etativ e grow th, but c e lls elongated and l a t e r a l buds developed in plan ts making re p ro d u c tiv e grow th. The f i r s t - 138 - and m o s t r e l i a b l e m o rp h o lo g ic a l evidence of re p ro d u c tiv e growth found in th is study w as longitudinal row s of c e lls in the rib m e r i s t e m and grow th of l a t e r a l b u d s . T h e s e m orp h o lo g ical changes p r e c e d e d flow er in itia tio n as m uch as 15 to 30 d ay s, w h e re a s ex p e rim e n ta l evidence p r e s e n t e d (75,84) on c am b ial activ ity , lim ite d phloem cell fo rm a tio n , i n c r e a s e d c e ll w all th ic k n e s s , f r e e r staining of c e r ta in t i s s u e s , and the a c c u m u la tio n cell in c lu sio n s o c c u r s h o rtly b efo re o r concom m itantly w ith flow er in itia tio n . Shoushan (79) found i n t r a - c e l l u l a r accu m u latio n of s t a r c h g r a n u le s ju s t p r i o r to flow er in itiatio n in L i lli u m . He also found th a t flo w er in itia ls a r o s e in the second the th ir d cell la y e r s of th e flanking m e r i s t e m , and le a f in itia ls a r o s e in the th ir d and fourth c ell l a y e r s . E x a m in a tio n of cabbage m e r i s t e m s in th is study c l e a r ly d e m o n s t r a te d th a t all l a t e r a l appendages a r o s e in the th ir d and fourth cell l a y e r s of th e flanking m e r i s t e m . The la s t m orp h olo gical evidence of r e p r o d u c tiv e growth was the o rig in of flow er p r im o r d ia in the axils of d w a r f le a f p r i m o r d i a . Since th e s e s e s s i le le a f p r im o r d ia eventually c e a s e d to d if f e r e n tia te th e y signified the final stage of the gradual t r a n s i t i o n f r o m v eg etativ e to re p ro d u c tiv e developm ent. Apices of cabbage shoots r e m a in e d unchanged as the s te m axis elongated and p ro d u c e d l a t e r a l ap p en d a g es. In v e g etativ e p lants th e s e l a t e r a l a p ­ p en d ag e s w e r e le a v e s and in re p ro d u c tiv e plants they w ere e ith e r dw arf l e a v e s , l a t e r a l sh o o ts, o r f lo w e r s . The te r m in a l apices did not d i f ­ f e r e n t i a t e into f lo w e r s , h o w ev er, flow ers a r o s e so closely to g e th e r n e a r th e a p ic e s of m a tu r e flow ering s ta lk s that th e y a p p e a re d to - 139 - th e u n aid ed eye to te r m i n a t e th e flow ering s ta lk . The i r r e g u l a r o r d e r of a p p e a r a n c e of flo w er p a r t s ( s e p a ls , s ta m e n s , p is til and la s tly p etals) a g r e e s w ith the findings of Thom pson (89) and is the com m on o r d e r for th e c r u c i f e r a e fa m ily . The findings in th e m o rp h o lo g ical stu d ies coincide with growth and flo w erin g r e s p o n s e s as d is c u s s e d in the phytohorm one th e o r y . An im p o r ta n t point con cern in g th e s e stu dies was th e g e n e ra l c e llu la r d i s ­ o rg a n iz a tio n in growing points h a r v e s te d F e b r u a r y 24 of m ed iu m size p la n ts s p r a y e d durin g th e induction tr e a t m e n t . Auxins as well as the s u b s titu te d phenoxy compounds have been found to activ ate growth by in c r e a s in g c e ll d iv isio n and cell elongation ( 2 ). P r o lif e r a tio n of v a r io u s t i s s u e s , developm ent of ro o ts and shoots fro m c a llu s, and g e n e r a l i n c r e a s e in growth re s u ltin g f r o m the application of phenoxy com pounds as r e p o r te d by B eal (2) and shown in this study, stron g ly in d ic a te th a t t h e i r m a in function m orp h o lo g ically is to encourage cell d iv is io n and gro w th . T h e r e a r e indications th a t c e llu la r o rg an iz atio n d u rin g n o r m a l see d s ta lk in itia tio n is involved in d eterm in in g th e growth p h a s e w hich follo w s. E vidence p r e s e n te d in th is study su g g ests th at C1PP applied d u rin g a cold tr e a tm e n t influenced c e llu la r o rg a n iz a tio n . U ntil f u r th e r w o rk is conducted on th is subject it would be p re s u m p tio u s to c la im th a t th i s phenom enon was brought about solely by the ch em ical tre a tm e n t. M a le ic h y d r a z id e a p p e a r s to p r e v e n t c e l l d iv is io n b y in h ib itin g m it o s is (1 6 ,2 2 ,2 4 ,3 4 ,6 9 ). A p p a ren tly t h is s u b s ta n c e d o e s not - 140 - i n t e r f e r e with c e ll elongation (34). C h elid o n ic acid ( 5 6 ) and alpha cy an o -B ( 2 , 4 , dichlorophenyl) a c r y lic acid (58) have also been found to inhibit plan t g ro w th . P la n t r e s p o n s e to the a c r y lic acid fo rm u la tio n a p ­ p e a r e d to be s i m i l a r to th at of m a le ic h y d ra z id e . One m a jo r d ifferen c e noted w as th a t a x i lla r y Ibud developm ent a p p e a re d not to be affected by alpha cy an o -B ( 2 ,4 , dichlorophenyl) a c r y lic a c id . F u rth er re s e a rc h w ith t h e s e c h e m ic a ls is n e c e s s a r y b e fo re th e ir auxin and a n ti-a u x in p r o p e r t i e s a r e fulfyunder stood. The genuine m e c h a n is m involved in the tr a n s f o r m a tio n f r o m one grow th p h ase to a n o th er r e m a in s o b s c u r e . W hether it be f r o m the f o r m a tio n of a sp ecific flo w er-in d u cing su b stan ce (florigen) o r some o th e r m o r e com plex phytohorm one s y s te m affords intriguing s p e c u la ­ tio n . The s y s te m ic n a tu re of re p ro d u c tiv e growth in cabbage is d e m ­ o n s tr a t e d f i r s t by th e re p ro d u c tiv e c h a r a c t e r i s t i c s of young developing l a t e r a l shoots; seco n d , by the production of nu m e ro u s l a t e r a l s e e d - s ta l k b r a n c h e s ; and th i r d , by th e d e v e rn a liz a tio n re s p o n s e as acc o m p lish ed by exposing m a tu r e flow ering plants to high t e m p e r a t u r e s . The in d i­ vidu al cell m o s t lik e ly e n c o m p a s se s th e b a s ic fa c to r o r fa c to r s i n ­ vo lv e d . The c o u r s e of developm ent in cabbage is governed by t e m p e r ­ a t u r e , lig h t, w a t e r , and the food and n u trie n t supply. The genetic c o n s titu tio n p la y s a m a jo r ro le in the type and quantity of r e s p o n s e . It is of im p o r ta n c e to 'know th at c e r ta in g ro w th -re g u la to ry su b sta n c e s u s e d p r o p e r l y a l t e r the quantity and quality of plant d evelo p m en t. To th is extent grow th and developm ent m ay be co n tro lled o r m anipulated - 141 - in such a m a n n e r as to obtain th e d e s i r e d plant response* - 142 - SUMMARY R e sp o n se to 2, 4 -dich lo ro p h en o x y acetic (2 ,4-D ); alpha, o r th o ch lo ro p h en o x y p ro p io n ic (C1PP); alpha n ap h th alen eacetic (NA); and ^ “triio d o b e n z o ic acid (T1BA); and m a le ic h y d razid e (MH) v a r ie d w ith c o n c e n tra tio n , tim e of application and size of cabbage s e e d in g s . C o n c e n tra tio n s in pp m w ere; 5, 1 0 , 15 and 20 2 ,4 -D ; 50, 1 0 0 , 250 and 500 C1PP and TIB A; 100, 250, 500 and 1000 NA; and 250 MH. The t h r e e p lan t s iz e s w e r e la r g e ( s te m d ia m e te r 9 m m . ) , m edium (6 m m . ) , and s m a ll (4 m m . ) . Most of the w ork d ealt with the m edium s iz e . Without an accom panying cold-induction of 38° F . fo r six w eeks no c h e m ic a l affected flo w erin g . Alm ost com plete inhibition of r e p r o d u c tiv e developm ent was achieved in m edium size Golden A c re s p r a y e d d u rin g cold-induction with 250 ppm C1PP. F lo w er in itiatio n and d ev elo p m en t was stim u late d in la r g e and m edium p lants by C1PP applied b e fo re o r a f te r induction. i l a r , but l e s s p ro n o u n ced . R esponse to 15 ppm 2 ,4 -D was s i m ­ Spraying la r g e plants during induction with 2 , 4 - D o r C1PP r e t a r d e d flow ering two w eek s. S p ra y s of 250 pp m of MH applied b efo re p a r ti a l induction of m e d iu m s iz e Round Dutch plan ts induced open head developm ent and when applied d u rin g p a r t i a l induction p ro m o ted seed stalk developm ent in m a ny p la n ts th a t o th e rw is e would have re m a in e d v e g e ta tiv e . A l­ though 50 p e r c e n t of the p la nts in th is tr e a tm e n t produced seed s ta lk s , none flo w e r e d . T e r m in a l buds w e re k illed and subsequent growth s u p ­ p r e s s e d fo r one y e a r by MH applied a fte r p a r t i a l induction. - 143 - Low concentrations of auxin-like ch em icals (2 ,4 -D , C1PP, NA) applied b efore cold w eather generally prom oted vegetative development and stim u lated growth in height for two months in medium siz e plants of both v a r ie t ie s . Proliferation of tis s u e s , m alform ation of le a v e s, and shoot and root developm ent in and around callu s tissu e w ere common w ith high concentrations of 2 ,4 -D and C1PP. Plants sprayed with TIBA in concentrations up to 500 ppm resem b led the con trols. The m o st reliab le m orphological changes indicative of reproduc­ tiv e developm ent w ere the form ation of longitudinal row s of c e lls in the rib m e r iste m , la tera l bud development and dwarfing of young le a v e s . Appearance of th ese changes varied among treatm ents but occurred about February 24 in la rg e and medium size p la n ts. Spraying large or m edium plants with C1PP (250 ppm) before or after cold-induction hastened the appearance of th ese ch a n g es. Large plants sprayed during induction in itiated reproductive growth two w eeks later than c o n tr o ls. Plants o f m edium s iz e sprayed with C1PP during induction showed no evidence o f reproductive growth as late as April 27. The ap ices did not becom e dom e-shaped but rem ained unchanged in the transition from vegetative to reproductive developm ent. L eaf and flow er in itia ls arose from p ericlin al c e ll division in the third and fourth c e ll la y e r s of the flanking m eristem just below the shoot ap ex. F lo w ers w ere produced la tera lly as w ere the lea v e s and did not term in ate the seed stalk . Flow er in itia ls w ere distinguished from - 144 - le a f in itia ls by g r o s s changes a s s o c ia te d with re p ro d u c tiv e grow th. When flo w e r in itia tio n b egan the subtending le a f b eca m e d w arfed . A fter s e v e r a l flo w e rs w e r e p ro d u ced th e le a f developed no f u r th e r th a n th e p r i m o r d i a l s ta g e . A m eth o d fo r n u m e r ic a lly evaluating the d e g re e of r e p r o ­ d u ction w as p r e s e n t e d . V egetative and re p ro d u c tiv e growth, and f l o r a l d ev elop m en t w e r e h is to lo g ic a lly p r e s e n te d and d is c u s s e d on the b a s i s of s y n th e s is , d is tr ib u tio n and economy of phyto horm one s . - 145 - LITERATURE CITED 1. Barnard, E . E . a n d R . L . W arden. 1950. The effect o f m a leic hydrazide on various vegetable cro p s. (A b st.) Paper p resen ted to North Central Weed Control Con­ feren ce . 1950. 2 . Beal, J. M . 1950. 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