IN T E R R E L A T I O N O F R E S P O N S E TO IN D O L E A C E T IC A C ID , D U R A TIO N A N D IN T E N S IT Y O F L IG H T , AND H E T E R O S IS IN T H E SN A PD R A G O N ( A N T IR R H IN U M M A JU S L . ) By JO H N B E R N A R D £ A R T N E R A TH ESIS S u b m i t t e d to t h e S c h o o l of G r a d u a t e S tu d ie s of M ic h i g a n S ta te C o lle g e of A g r i c u l t u r e a n d A p p lie d S c i e n c e in p a r t i a l f u l f i l l m e n t of th e r e q u i r e m e n t s f o r th e d e g r e e of D O C T O R O F P H IL O S O P H Y D e p a r t m e n t s of H o r t i c u l t u r e , B o ta n y a n d P l a n t P a t h o l o g y 1952 ProQuest Number: 10008311 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 10008311 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, Ml 4 8 1 06-1346 1- 11-0 ft) V ACKNOW LEDGMENT T h e a u t h o r w i s h e s to e x p r e s s h is s i n c e r e th a n k s to D o c t o r s H a m n e r , W ils o n a n d H a n e y u n d e r w h o s e g u i d ­ a n c e a n d s u p e r v i s i o n t h is i n v e s t i g a t i o n w a s u n d e r t a k e n . W ith o u t t h e i r c o o p e r a t i o n th e f u lf illm e n t of t h i s p r o j e c t c o u ld n e v e r h a v e b e e n c o m p le te d . He is a l s o g r e a t l y i n d e b te d to D r . S e ll a n d D r . B e n n e of th e A g r i c u l t u r a l C h e m i s t r y D e p a r t m e n t f o r t h e i r g u id a n c e a n d h elp in c h e m i c a l d e t e r m i n a t i o n s . G r a t e f u l a c k n o w le d g m e n t is a l s o due to M r . P h i l i p C o le m a n , E x p e r i m e n t S ta tio n p h o t o g r a p h e r f o r h is a s ­ s i s t a n c e on th e p h o t o g r a p h ic w o r k . T h e w r i t e r d e e p ly a p p r e c i a t e s th e f i n a n c i a l a i d of th e M ic h ig a n S ta te F l o r i s t A s s o c i a t i o n w h ic h m a d e p o s s i b l e th e u n d e r t a k i n g of t h i s p r o j e c t . T h e a u t h o r i s g r e a t l y i n d e b te d to h is w ife who h e lp e d in th e c o n d u c tin g of th e e x p e r i m e n t s a n d c o m p i l a t i o n of d a ta a n d ty p in g . W ith o u t th e i n s p i r a t i o n of m y w ife, t h is w o r k w o u ld n e v e r h a v e b e e n c o m p le te d , a n d to w h o m th e r e s u l t s a r e h e r e w i t h d e d ic a te d . IN T E R R E L A T IO N O F R E S P O N S E TO IN D O L E A C E T IC A CID, DU RA TION AND IN T E N S IT Y O F L IG H T , AND H E T E R O S IS IN T H E SNA PD R A G O N (A N T IR R H IN U M M AJUS L .) By Jo h n B e rn a rd G artn er AN ABSTRACT S u b m it t e d to th e S c h o o l of G r a d u a t e S tu d ie s of M ic h i g a n S ta te C o lle g e of A g r i c u l t u r e a n d A p p li e d S c i e n c e in p a r t i a l f u lf i l l m e n t of th e r e q u i r e m e n t s f o r th e d e g r e e of D O C T O R O F P H IL O S O P H Y D e p a r t m e n t s of H o r t i c u l t u r e , B o ta n y a n d P l a n t P a t h o l o g y Y ear APPROVED - O S,., y . 1952 C_. - Jo h n B. G a r tn e r It w a s fo u n d th a t A n t i r r h i n u m m a j u s L . d e f in it e ly e x ­ h ib its h e te r o s is . A n i n t e r r e l a t i o n s h i p w a s fo u n d b e tw e e n in d o le a c e t i c a c i d , lig h t i n t e n s i t y a n d th e d e g r e e of h e t e r o ­ sis . T h e d e g r e e of h e t e r o s i s e x h ib ite d w a s no t th e s a m e a t a l l s e a s o n s of th e y e a r . H e te r o s is w as m e a s u re d by ta k in g t h e i n c r e a s e cf th e F j o v e r th e a v e r a g e of th e two p a r e n t s b o th a s to i n c r e a s e in h e ig h t a n d i n c r e a s e in d r y w e ig h t. T h e d e g r e e of h e t e r o s i s e x h i b i t e d in A . m a j u s i s c o r ­ r e l a t e d w ith s o l a r r a d i a t i o n . W hen s o l a r r a d i a t i o n w a s lo w th e d e g r e e of h e t e r o s i s w a s no t a s p r o n o u n c e d a s w h e n s o l a r r a d i a t i o n w a s h ig h . T r e a t m e n t w ith in d o le a c e t i c a c i d i n d i c a t e d t h a t th e h y b r i d s s h o w e d a g r e a t e r e p i n a s ti c r e s p o n s e th a n e i t h e r of th e p a r e n t s . T h is e p i n a s t i c r e s p o n s e w a s a l s o c o r r e l a t e d w ith so la r r a d i a t i o n a n d a g r e a t e r e p i n a s t i c r e s p o n s e w a s fo u n d u n d e r low lig h t i n t e n s i t y th a n u n d e r h ig h lig h t i n t e n ­ s it y . B y u s in g a b i o l o g i c a l t e s t it w a s fo u n d t h a t th e i n b r e d s h a v e a m o r e e f f e c tiv e m e c h a n i s m of i n a c t i v a t i n g o r in h ib itin g th e e f f e c t s of in d o le a c e t i c a c i d t h a n th e h y b r i d . It w a s fo u n d t h a t s o l a r r a d i a t i o n i n f l u e n c e s h e t e r o s i s in A . m a j u s . T h e e x p r e s s i o n of h e t e r o s i s in A . m a ju s c a n b e d i r e c t l y c o r r e l a t e d w ith lig h t i n t e n s i t y a n d a s t h e lig h t i n t e n s i t y J o h n B . G artner - 2- i n c r e a s e s th e d e g r e e of h e t e r o s i s i n c r e a s e s . T h e i n b r e d s p o s s e s s a m e c h a n i s m of i n a c t i v a t i n g in d o le a c e tic a cid . T h is i n a c t i v a t i o n i n c r e a s e s a s lig h t i n t e n s i t y i n c r e a s e s a n d t h i s p o s s i b l y c o u ld b e th e e x p l a n a t i o n of h e t e r o ­ s i s in A . m a j u s . T h e r e i s l e s s i n a c t i v a t i o n of g r o w th s u b ­ s t a n c e s in th e h y b r i d s th a n i n th e i n b r e d s u n d e r h ig h lig h t in te n sitie s. T h is r e s u l t s in a n i n c r e a s e d g r o w th r a t e in th e h y b r i d s a n d c o u ld b e th e r e a s o n w hy th e h y b r i d s show a g r e a t e r a m o u n t of h e t e r o s i s u n d e r h ig h l ig h t t h a n u n d e r low lig h t in te n s itie s . John B e rn a rd G a rtn e r C a n d id a te f o r th e d e g r e e of D o c to r of P h i l o s o p h y F i n a l e x a m in a tio n , J u l y 7, 1952, 2:00 P . M . , H o r t i c u l t u r e S em in ar Room . D is se rta tio n : I n t e r r e l a t i o n of R e s p o n s e to In d o le A c e t i c A c id , D u r a t i o n a n d I n t e n s i t y of L ig h t, a n d H e t e r o s i s in th e S n a p d r a g o n ( A n t i r r h i n u m M a ju s L . ) O u tlin e of S tu d ie s M a jo r s u b je c ts : H o r t i c u l t u r e a n d B o ta n y B io g ra p h ic a l Ite m s B o r n , M a r c h 23, 1918, C le v e la n d , Ohio U n d e r g r a d u a t e S tu d ie s , O hio S ta te U n i v e r s i t y , 1938-42 G r a d u a t e S tu d ie s , M ic h i g a n S ta te C o lle g e , 1946-49, 1951-52. E x p e r i e n c e : U n i t e d S t a t e s N av y , 1 94 2 -4 6 . A t t a i n e d the r a n k of F u l l L i e u t e n a n t a n d c o m m a n d in g o f ­ f i c e r of t h r e e v e s s e l s d u r in g t h i s p e r i o d . S u p e r i n t e n d e n t of B e a l G r e e n h o u s e s , M i c h i ­ g a n S ta te C o lle g e 19 47 -49 . H o r t i c u l t u r e E x t e n s i o n S p e c i a l i s t N o r t h C a r o l i n a S ta te C o lle g e 1949-51. G r a d u a t e A s s i s t a n t , M ic h i g a n S ta te C o lle g e 1951-52. M e m b e r of P i A lp h a Xi a n d S o c ie ty of th e S ig m a X i. TA B L E OF CONTENTS IN T R O D U C T IO N I R E V IE W O F L I T E R A T U R E 4 M A T E R IA L S A ND M E T H O D S 13 A. P la n ts 13 B. M e a s u r e m e n t s 14 C . D r y W e ig h t D e t e r m i n a t i o n s 15 D. R e s p o n s e to In d o le A c e t i c A c i d 16 E . B io lo g ic a l T e s ts 17 F . E f f e c t of L i g h t I n te n s i t y 18 G. S o l a r R a d i a t i o n 19 RESULTS I. H e t e r o s i s II. P h y s i o l o g i c a l R e s p o n s e 20 20 25 A . P h y s i o l o g i c a l r e s p o n s e to in d o le a c e t i c a c id 25 B . B io l o g i c a l T e s t s 32 III. L i g h t I n t e n s i t y O b s e r v a t i ons 36 A . E f f e c t of l i g h t on h e t e r o s i s 36 B . E f f e c t of li g h t on th e p h y s io l o g i c a l r e s p o n s e to in d o le a c e t i c a c i d 43 DISCUSSION 47 CO N CLU SIO N 52 B IB L IO G R A P H Y 53 A P P E N D IX i IN T R O D U C T IO N T h e s u p e r i o r v i g o r of th e p r o g e n y of tw o u n r e l a t e d i n b r e d lin es has b een o b s e rv e d and u tiliz e d for m any y e a r s . T h i s p h e n o m e n o n h a s fo u n d m o r e a p p l i c a t i o n s c o n t i n o u s ly f r o m p r e - M e n d e l i a n t i m e s to th e p r e s e n t a n d a d d i ti o n a l a p p l i c a t i o n s w ill u n d o u b te d ly b e m a d e in th e f u t u r e . T h e t e r m h y b r i d v i g o r o r i g i n a l l y a p p l i e d to t h i s p h e ­ n o m e n o n h a s f a l l e n in to s o m e d i s r e p u t e . It h a s b e e n u s e d in c a s e s w h e r e th e p a r e n t s w e r e n o t i n b r e d , a p p l ie d to g e n e r a t i o n s l a t e r th a n th e F j , a n d c a m e to im p l y a c o n ­ s i s t e n t s u p e r i o r i t y w h ic h i s n o t n e c e s s a r i l y th e c a s e . S h u ll (39) p r o p o s e d t h e t e r m h e t e r o s i s to d e s c r i b e th e v i g o r d i f f e r e n c e , p o s i t i v e o r n e g a tiv e , b e t w e e n th e F^ a n d th e p a ­ re n ta l av erag e. M o s t o f t h e w o r k on h e t e r o s i s h a s b e e n done on c o r n . T h e A m e r i c a n I n d ia n s k n e w w ith o u t e x p e r i m e n t a l e v id e n c e t h a t p la n tin g of m i x t u r e s of c o r n w o u ld i n c r e a s e th e y i e ld . H o w e v e r , c o r n i s n o t th e o n ly c r o p t h a t s h o w s h e t e r o s i s . T h e i n c r e a s e d y i e l d of h y b r i d o v e r i n b r e d c o r n i s v e r y c o n s id e ra b le . G r e a t e r y ie l d s a r e o b ta in e d w ith l e s s e f f o r t . T h e u s e of h y b r i d c o r n , g a v e a s u r p l u s f o r th e U n ite d S t a t e s d u r in g th e w a r a n d p o s t w a r d i s t r e s s p e r i o d s . T h is w a s g r e a t en o u g h to h e lp fe e d , n o t o n ly th e U n ite d S t a t e s , b u t o t h e r c o u n t r i e s a s w e l l. It w o u ld h a v e t a k e n a g r e a t d e a l m o r e m a n p o w e r to p r o d u c e t h e s e s a m e y i e l d s if it w e r e n o t for h e te r o s is . T h e v a l u e of h y b r i d c o r n to th e A g r i c u l t u r a l i n d u s t r y a n n u a l l y w i l l m o r e th a n p a y f o r a l l th e r e s e a r c h w o r k t h a t h a s e v e r b e e n done in th e f ie l d of A g r i c u l t u r e . T h e n ew a p p l i c a t i o n s of h e t e r o s i s o f f e r g r e a t e r p r o m i s e f o r th e f u t u r e th a n h a v e b e e n r e a l i z e d in th e p a s t . a s o n io n s O th e r p lan ts such to m ato es, e t c . , a s w e ll a s m any o rn a m e n ta l c ro p s, sh o w m a r k e d i n c r e a s e in g r o w th of h y b r i d s o v e r i n b r e d s . F o r t h i s i n v e s t i g a t i o n of h e t e r o s i s , th e s n a p d r a g o n , A n t i r r h i n u m m a ju s w a s c h o s e n a s th e t e s t p l a n t . H e te ro sis in t h i s c r o p i s n o t r e c o r d e d in th e s c i e n ti f i c l i t e r a t u r e a lth o u g h i t s e f f e c t is a t t e s t e d b y th e r a p i d i n c r e a s e in th e p o p u l a r i t y of F | h y b r i d s in c o m m e r c i a l F l o r i c u l t u r e . A n y n ew i n f o r m a t i o n on h e t e r o s i s in t h is c r o p o f f e r s i m ­ m e d i a t e a d v a n ta g e . C u ltu rally , sn ap d rag o n s a r e a d v a n ta g e ­ o u s b e c a u s e l a r g e p o p u la tio n s m a y b e g ro w n in c o m p a r a t i v e l y s m a l l s p a c e a n d s h o r t t i m e a t a n y s e a s o n o f th e y e a r . G e n e t i c a l l y it is d ip lo id h a v in g s i x t e e n s o m a t i c c h r o m o s o m e s a n d a c o n s i d e r a b l e b o d y of l i t e r a t u r e s h o w s e x p e c t e d i n h e r i ­ t a n c e of u n it f a c t o r s , B a u e r (6 ). It i s s e l f f e r t i l e , e a s i l y e m a s c u l a t e d a n d p o ll i n a t e d , a n d p r o d u c e s a s m a n y a s 500 s e e d s f r o m a s in g le p o l l in a t i o n . It a p p e a r s t h a t no o t h e r p l a n t o f f e r s a l l of t h e s e a d v a n t a g e s f o r th is ty p e of w o r k . -3- I n b r e d a n d h y b r i d s n a p d r a g o n s d if f e r in t h e i r r e g i o n a l ad ap tatio n . In th e a u t h o r ’s e x p e r i e n c e o u ts ta n d in g h y b r i d s f r o m m o re n o r th e r n la titu d e s have not b e e n ad v an tag eo u s in N o r t h C a r o l i n a . S in c e t h e s e d i f f e r e n c e s w e r e k no w n to e x i s t th e i n v e s t i g a t i o n of t h is c r o p o f f e r e d p r o m i s e of u s e ­ fu l i n f o r m a t i o n . -4- R E V IE W O F L I T E R A T U R E It i s c o m m o n l y k no w n to c o m m e r c i a l g r o w e r s t h a t h y ­ b r i d s a r e m u c h s u p e r i o r to i n b r e d s in s e v e r a l s p e c i e s of sh ru b s and e v e rg re e n s. T h is h y b r id a d v a n t a g e i s m a i n ­ ta in e d by a s e x u a l p ro p a g a tio n . A s e a r c h of th e l i t e r a t u r e r e v e a l e d l i t t l e s c ie n ti f i c i n f o r m a t i o n c o n c e r n i n g h e t e r o s i s in s n a p d r a g o n s . P ost (35) h a s r e c o m m e n d e d th e u s e of h y b r i d s n a p d r a g o n s . S in c e l i t t l e i s k now n c o n c e r n i n g h e t e r o s i s of A n t i r r h i n u m , a s e a r c h of th e l i t e r a t u r e w a s m a d e to d e t e r m i n e w h a t w a s k n o w n on o t h e r p l a n t s . E a r l y p l a n t h y b r i d i s t s in c lu d in g K o l r e u t e r (27) in th e e i g h t e e n th c e n tu r y , G a r t n e r (18) in th e n in e t e e n t h c e n t u r y n o t e d i n c r e a s e d v i g o r of h y b r i d s . S in c e t h i s t i m e c o n s i d ­ e r a b l e e x p e r i m e n t a t i o n h a s b e e n c a r r i e d ou t to f in d a b a s i s for h e te ro sis. E v e n to d a y a f t e r m a n y y e a r s r e s e a r c h , no o n e h a s c o m p l e t e l y e x p l a i n e d th e e x a c t m e c h a n i s m . S in c e 1900 s o m e r e a s o n a b l y s a t i s f a c t o r y h y p o th e s i s of h e t e r o s i s have b een p re se n te d . T he h y p o th esis th at is m o s t fa v o re d i s th e one of E a s t a n d J o n e s (12, 13, 14, 15, 16, 22, 23, 24) i n ­ v o lv in g d o m in a n c e . J o n e s (22) e x p l a n a t i o n of h e t e r o s i s i n v o lv e s d o m i ­ n a n c e w e l l e x e m p l i f i e d in P i s u m s a t i v u m L . K e e b le a n d -5- P e l l e w (26) h a v e sh o w n t h a t tw o s h o r t p l a n t s c r o s s e d g av e u n ifo rm ly ta ll p ro g en y . p a r e n t c o n t r ib u t e d a G e n e tic a n a l y s i s h a s sh o w n t h a t one r e c e s s iv e fa c to r fo r sh o rt in te rn o d e s a n d a d o m in a n t f a c t o r f o r m a n y n o d e s w h ile th e o t h e r p a r e n t c o n t r i b u t e d th e a l l e l e s d o m in a n t long i n t e r n o d e s a n d r e ­ c e s s i v e few n o d e s . T h e F j s h o w in g th e d o m in a n t a l l e l e s p r o d u c e s t a l l p l a n t s h a v in g m a n y lo n g i n t e r n o d e s . C r o p s w h e r e h e t e r o s i s i s i m p o r t a n t do n o t p r o d u c e in F 2 a n d l a t e r g e n e r a t i o n s th e h o m o z y g o u s d o m in a n t s i z e f a c ­ t o r s t h a t m ig h t b e e x p e c t e d f r o m F j p e r f o r m a n c e . As J o n e s (25) i n d i c a t e d i t i s a l m o s t i m p o s s i b l e b y s tu d y in g t h e g e n e t i c s of h e t e r o s i s to o b ta in th e e x p e c t e d g e n e tic r a t i o in t h e F 2 . W hen M o r g a n (34) f i r s t d i s c o v e r e d lin k a g e , J o n e s (25) u s e d t h is f a c t to sh o w w h y th e F w o u ld n o t g iv e th e e x p e c t e d 2 p r o p o r t i o n of v i g o r o u s in d i v id u a l s . If th e g en e f o r t h e lo ng i n t e r n o d e s w a s c l o s e l y c o u p le d w ith th e g en e f o r a s m a l l n u m b e r of n o d e s on o n e c h r o m o s o m e , a n d th e a l l e l e f o r a l a r g e n u m b e r of n o d e s w a s c l o s e l y c o u p le d w ith th e a l l e l e f o r s h o r t i n t e r n o d e s o n th e h o m o lo g o u s c h r o m o s o m e t h e s e f a c t o r s w o u ld b e r e p u l s i o n lin k e d a n d w o u ld g iv e a low r a t e of c r o s s i n g o v e r . T h e p r o p o r t i o n of v i g o r o u s i n d iv id u a ls w o u ld b e r e d u c e d a n d th e p r o b a b i l i t y of th e h o m o z y g o u s d o m in a n t r e c o m b i n a t i o n w o u ld b e th e s q u a r e of th e f r e q u e n c y of th e low r a t e o f c r o s s i n g o v e r . S in g le to n (40) h a s c a l c u l a t e d t h a t 2000 t i m e s th e la n d a r e a of th e e a r t h w o u ld b e n e c e s s a r y to g ro w en o u g h c o r n p l a n t s to s ta n d a r e a s o n a b l e c h a n c e of r e c o v e r i n g a c o m ­ p l e t e l y h o m o z y g o u s d o m in a n t, if t h i r t y g e n e s w e r e in v o lv e d in h e t e r o s i s w ith o u t l in k a g e . S in c e h e t e r o s i s u s u a l l y a p p e a r s to b e d e p e n d e n t o n m u l ­ t i p l e f a c t o r s a n d in v o lv e s lin k a g e , it i s a l m o s t i m p o s s i b l e to r e c o v e r a h o m o z y g o u s p la n t in th e F ^ o r l a t e r g e n e r a ­ ti o n s t h a t e q u a ls th e F^ in v i g o r . It h a s b e e n sh o w n b y E a s t (15) t h a t th e s e g r e g a t i n g p o p u la tio n c o n tin u a lly r e d u c e s in v i g o r e a c h y e a r u n t i l it r e a c h e s a s t a t i c p o s i t i o n w h e n it is e ffectiv ely h o m ozygous. B y c o n tin u a l in b r e e d in g , e s p e ­ c i a l l y w ith s in g l e p l a n t s e l e c t i o n s , th e y i e l d w i ll b e r e d u c e d u n til e f f e c tiv e h o m o z y g o s i t y i s o b ta in e d . H o w e v e r, c o m p le t e h o m o z y g o s i t y i s v e r y s e l d o m o b ta in e d a n d E a s t (13) h a s sh o w n t h a t a f t e r e ig h t g e n e r a t i o n s , n i n e t y - f i v e p e r c e n t h o m o z y g o s it y w o u ld b e a p p r o a c h e d . It i s v e r y d if f ic u lt to d e t e r m i n e w h a t f a c t o r s c o n t r o l h e t e r o s i s , s in c e i t i s d if f ic u lt to m e a s u r e g r o w th . T o d a te , t h e r e a r e c o m p a r a t i v e l y few m e th o d s of d e t e r m in i n g r a t e s of g r o w th of one ty p e o r a n o t h e r b e c a u s e it i s d iff ic u lt to c o n t r o l so m a n y of t h e in f lu e n c in g e x t e r n a l e n v i r o n m e n t a l f a c t o r s w h ic h p l a y a n i m p o r t a n t r o l e in th e r e s p o n s e of a c r o p to i t s t o t a l i n h e r e n t v i g o r . -7- T h e e f f e c t of h e t e r o s i s in p l a n t s c a n n o t a lw a y s b e m e a s ­ u r e d b y a n i n c r e a s e i n s i z e of th e plant. It m a y b e e v id e n t a s a n i n c r e a s e i n y i e l d o r a n i n c r e a s e in d r y w e ig h t o r a n i n ­ c r e a s e in n u t r i t i o n a l v a lu e . F o r e x a m p le , t o m a to h y b r i d s do n o t n e c e s s a r i l y sh o w a n i n c r e a s e in s i z e of f r u i t , b u t m a y g r e a t l y i n c r e a s e th e n u m b e r of i n f l o r e s c e n c e a s w e l l a s th e to ta l y ield of fru it. W h a le y (50, 51) s u g g e s t e d t h a t h y b r i d v ig o r i s due to h e t e r o z y g o s i t y , a n d th e m o r e h e t e r o z y g o u s th e in d iv id u a l t h e m o r e v i g o r o u s t h e in d iv id u a l. In s o m e w a y s t h i s s e e m s to f it in to th e p i c t u r e a n d c o u ld p o s s i b l y e x p la in w h y th e F ^ a n d s u c c e e d in g g e n e r a t i o n s g r a d u a l l y d e c r e a s e in v i g o r u n ­ t i l h o m o z y g o s i t y i s o b ta in e d . E x a m p les have b een re p o rte d b y W h a le y (51) in w h ic h t h e f u r t h e r a p a r t th e p a r e n t s in r e l a ­ tio n s h ip , t h e m o r e v i g o r o u s t h e h y b r i d s . H o w e v e r, E a s t (12, 13) h a s sh o w n b y i n b r e e d i n g s i s t e r s in g le p l a n t s e l e c t i o n s of a s e g r e g a t i n g p o p u la tio n to e f f e c tiv e h o m o z y g o s i t y a n d t h e n c r o s s i n g , t h a t h e t e r o s i s w a s e v id e n t a lth o u g h th e l i n e s w e r e c lo se ly re la te d . T h i s i s th e b a s i s f o r S h u ll (39) c o in in g th e t e r m h e t e r o s i s m e a n in g t h a t th e in d iv id u a l w a s e x t r e m e l y h e te ro z y g o u s. P r i o r to 1930, d o m in a n c e a n d lin k a g e w e r e f a i r l y w e l l a c ­ c e p t e d a s a b a s i s of h e t e r o s i s . A s h b y (2, 3, 4, 5) w a s one of th e f i r s t to d i s c u s s h e t e r o s i s a s r e l a t e d to g r o w th f a c t o r s . -8- F r o m h i s i n v e s t i g a t i o n s , he a s s u m e d t h a t h y b r i d c o r n h a d a p p r o x i m a t e l y th e s a m e g r o w th r a t e a s i t s l e s s v i g o r o u s p a ­ r e n t s , a n d t h a t t h e h y b r i d d id n o t v a r y f r o m e i t h e r of i t s p a r e n t s a s to c e l l s i z e , p h o to s y n th e ti c a c t i v i t y o r r e s p i r a ­ tio n . A s a r e s u l t , th e f la tte n i n g of i t s g r o w t h c u r v e d u r in g th e g r a n d p e r i o d of g r o w t h w o u ld b e th e s a m e in i n b r e d s a s in h y b r i d s . He c o n c lu d e d t h a t th e only a d v a n ta g e th e h y b r i d h a d o v e r it s l e s s v i g o r o u s p a r e n t s w a s a l a r g e r e m b r y o h a v ­ ing a h i g h e r p e r c e n t a g e of g e r m i n a t i o n , a n d t h a t t h i s a d v a n ­ ta g e w a s m a i n t a i n e d th ro u g h o u t th e g r a n d p e r i o d of g r o w th a n d r e s u l t e d in a s u p e r i o r p la n t. L i n d s t r o m (29, 30, 31) s i m i l a r l y c a m e to th e c o n c lu s io n t h a t th e h y b r i d s m a i n t a i n e d a n i n i t i a l a d v a n t a g e in s i z e o v e r th e i n b r e d s . He s t a t e d t h a t a s m a l l i n i t i a l a d v a n t a g e in s i z e in th e F^ c e l l s o r e m b r y o w o u ld m u l t i p l y v e r y r a p i d l y a n d w o r k on th e c o m p o u n d i n t e r e s t law a n d c o u ld p o s s i b l y a c c o u n t f o r t h e s u p e r i o r i t y of th e h y b r i d s . L i n d s t r o m (31) a l s o d e ­ c a p i t a t e d s o m e h y b r i d s to r e d u c e a n y i n i t i a l s i z e a d v a n ta g e a n d s h o w e d t h a t th e y f in a ll y e x c e e d e d th e p a r e n t a l s t r a i n s a s to d r y w e ig h t. H o w e v e r , he s u p p o s e d t h a t t h i s p r o c e d u r e d id n o t e n t i r e l y e l i m i n a t e th e e m b r y o n ic c a p i t a l a n d i n i t i a l a d v a n t a g e , a n d h e c l a i m e d t h a t th e m e r i s t e m s m a i n t a i n e d t h i s a d v a n ta g e . F u r t h e r w o r k a lo n g t h i s lin e h a s f a i l e d to p r o v e t h a t th e e m b r y o i s a n y l a r g e r in th e h y b r i d s th a n in th e i n b r e d s , a n d in s o m e c a s e s th e h y b r i d s w e r e fo un d to be -9- i n t e r m e d i a t e in s i z e , y e t t h e y s t i l l d i s p l a y e d m o r e v ig o r th a n e i t h e r of th e p a r e n t s . E a s t (15) p o i n t e d o ut t h a t t h e r e a r e s e v e r a l r e c o r d e d c r o s s e s w h e r e h y b r i d s e e d s w e r e n o t a s l a r g e a s t h o s e of th e la r g e r p a r e n ts . M o s t of t h e s e a r e in th e l e g u m i n o s a e w h e r e t h e r e i s v i r t u a l l y no e n d o s p e r m . H e n c e , i t w o u ld a p p e a r th a t th e e m b r y o s i z e a lo n e c a n n o t be th e i m p o r t a n t fa c to r in h y b rid v ig o r. I n th e p a s t few y e a r s , t h e r e h a s b e e n c o n s i d e r a b l e s p e c u l a t i o n on th e o n e - g e n e o n e - e n z y m e t h e o r y on c o n ­ t r o l l i n g p l a n t g r o w th . T a tu m (43) h a s sh o w n t h a t e y e c o l o r in D r o s o p h il a is a c h e m ic a l actio n and i s g e n e -c o n tro lle d . H a n e y (21) h a s sh o w n a s e q u e n c e of g e n e a c t i o n in c o l o r i n h e r i t a n c e in s n a p d r a g o n . T h e d o m in a n t a l l e l e f o r w h ite m u s t b e p r e s e n t f o r e x p r e s s i o n of a n y c o l o r othe;r th a n w h ite . T h e d o m in a n t a l l e l e s f o r b o th w h ite a n d i v o r y m u s t b e p r e s e n t to sh o w a n t h a c y a n i n p i g m e n t a t i o n o r i t s m o d i f ic a t i o n b y d i lu tio n o r i n t e n s i t y g e n e s . A l l th e m o s t r e c e n t w o r k on p h y s io lg ic a l g e n e t i c s h a s d e m o n s t r a t e d t h a t c h e m i c a l p r o c e s s e s in v o lv in g e n z y m e s a r e * g en e-co n tro lled . T a t u m a n d B e a d le (7, 44) h a v e sh o w n t h a t m u t a n t s t r a i n s of N e u r o s p o r a a r e u n a b le to s n y t h e s i z e c e r ­ ta in e s s e n tia l g ro w th s u b s ta n c e s . S u ch m u t a n t s c o u ld b e o b t a in e d b y t r e a t i n g n o r m a l s t r a i n s w ith m u t a g e n i c a g e n t s . -10- W h en t h e s e m u t a n t s t r a i n s o f N e u r o s p o r a a r e s u p p li e d w ith th e d e f i c i e n t g r o w t h s u b s t a n c e s , th e y a r e a b le to m a k e a s m u c h g r o w t h a s th e n o r m a l s t r a i n s of fu n g i. W o rk of t h i s n a t u r e h a s i n d i c a t e d t h a t h e t e r o s i s m a y b e th e r e s u l t of m o r e e f f i c ie n t p r o d u c t i o n of g r o w t h s u b s t a n c e s . T h is e x p l a n a t i o n w o u ld n o t d i s p r o v e a n y of th e p r e v i o u s t h e o r i e s b u t w o u ld c o n f i r m t h e s e c o n c e p t s of h e t e r o s i s . R o b b in s (36) h a s sh o w n t h a t e x t r a c t s of p a r t i a l l y g e r m ­ i n a t e d i n b r e d a n d h y b r i d c o r n , d i f f e r e d s i g n i f i c a n t ly a s m e d i a f o r th e g r o w th of c e r t a i n s e l e c t e d s t r a i n s of fu n g i. T h e o n e s g ro w in g in th e h y b r i d e x t r a c t w e r e m u c h s u p e r i o r to t h o s e g r o w n on i n b r e d e x t r a c t s . T h is m a y i n d i c a t e t h a t h y b r i d s h a v e a m o r e e f f i c i e n t p r o d u c t io n of g r o w th s u b ­ s ta n c e s than th e ir le s s v ig o ro u s in b re d p a r e n ts . W h a le y a n d L o n g (52) h a v e sh o w n t h a t u n d e r c e r t a i n c o n ­ d i t i o n s e x c i s e d r o o t s of h y b r i d t o m a t o e s a n d h y b r i d c o r n g r o w n in c u l t u r e s sh o w c o n s i d e r a b l y m o r e g r o w th th a n t h o s e of t h e i r i n b r e d p a r e n t s . R o b b in s (37) u s in g a c r o s s of i n b r e d l i n e s of L y c o p e r s i c u m p i m p i n e l l i f o l i u m a n d L y c o p e r s i c u m e s c u l e n t u m , fo u n d in s o lu ti o n s s u p p le m e n t e d b y t h ia m i n e , p y r id o x i n e , o r n i c o t i n a m i d e , s e p a r a t e l y o r in c o m b i n a t io n s o f two, th a t th e ro o ts g rew m o re ra p id ly an d p ro d u c e d m o re d r y m a t e r i a l th a n t h o s e of th e i n b r e d p a r e n t s . He s h o w e d t h a t t h e r o o t s of P a r e n t A s h o w e d a g r e a t e r r e s p o n s e to p y r id o x i n e th an P a r e n t B. T h e r o o t s of P a r e n t B sh o w e d a g r e a t e r r e s - -11- p o n s e to n i c o t i n a m i d e t h a n t h o s e of P a r e n t A . H ow ever, P a ­ r e n t B a p p r o a c h e d th e F^ in s o lu tio n c o n ta in in g a l l t h r e e su p p le m e n ts. W h a le y (51, 53) h a s fo u n d in i n b r e d l i n e s of m a i z e , of th e v a r i e t i e s P i p e , P a w n e e , a n d t h e i r r e c i p r o c a l h y b r id s , m a r k e d d i f f e r e n c e s in t h e i r r e a c t i o n s to lig h t c o n d itio n s . W ith c e r ­ t a i n lig h t i n t e n s i t i e s , th e h y b r i d s sh o w e d a s u p e r i o r i t y a n d a t o t h e r i n t e n s i t i e s th e i n b r e d s a p p r o a c h e d th e h y b r i d s in s i z e . M a lin o w s k y (32, 33) n o te d t h a t h e t e r o s i s in b e a n s p r o d u c e d a r e s p o n s e s i m i l a r to t h a t d e s c r i b e d b y W h a le y (51) in m a i z e u n d e r c e r t a i n e n v i r o n m e n t a l c o n d itio n s . G o l d s c h m i d t (19, 20) h a s sh ow n th a t g e n e s in flu e n c e enzym e re a c tio n s. T h is i s f u r t h e r c o n t r o l l e d b y e n v i r o n m e n t . P h e n o c o p i e s of m o th s m a y b e o b ta in e d b y c h a n g in g th e e x t e r n a l e n v iro n m e n t. C h a n g e d e n v i r o n m e n t r e s u l t e d in a d u p l i c a t io n of th e w in g p a t t e r n of a n o t h e r g e n e tic s t r a i n of m o th . T hese p h e n o c o p ie s sh ow t h a t u n d e r d i f f e r e n t e n v i r o n m e n t a l c o n d itio n s , th e c o u r s e o r s e q u e n c e of c h e m i c a l r e a c t i o n s m a y b e a l t e r e d a n d a s a r e s u l t g e n e a c t i o n w ill b e m o d ifie d . V an O v e r b e e k (46) h a s sh o w n th a t " L a z i n e s s " in m a i z e i s d ue to a n a b n o r m a l d i s t r i b u t i o n a n d p r o d u c t io n of g r o w th s u b ­ s ta n c e s. G a l s to n (17) h a s sh o w n t h a t r ib o f la v i n in th e p r e s e n c e of l ig h t i n a c t i v a t e s in d o le a c e t i c a c i d . It a l s o c a n b e d e m o n s t r a t e d t h a t u n d e r v a r y i n g i n t e n s i t i e s a n d q u a l i t i e s of lig h t in d o le a c e t i c -12- is in a c tiv a te d . W ittw e r (54, 55) h a s sh o w n t h a t in th e u s e of in d o le a c e t i c a c i d f o r f r u i t s e t, g r e a t e r e f f i c i e n c y w a s o b ta in e d a t low th a n a t h ig h lig h t i n t e n s i t i e s . Skoog (41, 42) h a s fo u n d t h a t a d e n in e in th e p r e s e n t of lig h t w ill i n a c t i v a t e in d o le a c e t i c a c i d . A good e x a m p l e of t h i s i s th e o r i g i n a l w o r k on p h o t o t r o p i s m . B u r k h o l d e r a n d J o h n s t o n (9), B o y s e n J e n s e n (8), W en t (49) a n d o t h e r s h o w e d t h a t lig h t i n a c t i v a t e s th e g r o w th s u b s t a n c e on th e lig h t s id e of th e c o l e o p ti l e r e s u l t i n g in i t s b e n d in g t o w a r d s t h e lig h t. It has b een o b s e rv e d for m any y e a r s by m any b o t a n i s t s , t h a t p l a n t s g ro w n i n t h e A lp in e a r e a s a r e d w a r fe d , W en t a n d T h im a n n (49). A p o s s i b l e e x p l a n a t i o n is t h a t t h e y r e ­ c e iv e g r e a t e r q u a n t i t i e s of u l t r a v i o l e t lig h t w h ic h is k n o w n to i n a c t i v a t e th e au x in , in d o le a c e t i c a c id , a n d h e n c e r e s u l t in l e s s g r o w th . I t i s a p p e a r e n t t h a t w h ile th e c h e m i c a l r e a c t i o n of p l a n t s m a y b e g e n e - c o n t r o l l e d , e n v i r o n m e n ta l f a c t o r s m a y a l t e r i t s m o d e of a c t i o n . -13- M A T E R IA L S AND M ETH O D S A. P la n ts Tw o i n b r e d l i n e s of A n t i r r h i n u m m a j u s L . a n d th e h y ­ b r i d p r o d u c e d f r o m th e c r o s s b e tw e e n t h e s e two i n b r e d s w e r e c h o se n a s e x p e rim e n ta l te s t su b je c ts fo r th is p r o je c t. A. m a ju s w as ch o sen s in c e th is s p e c ie s d isp la y s h e te r o s is w hen tw o i n b r e d l i n e s a r e c r o s s e d ; a l s o th e g e n e t i c s of t h i s s p e c i e s i s f a i r l y w e ll know n. B y u s in g A . m a j u s a s a t e s t s u b je c t, a l a r g e p o p u la tio n c a n b e g r o w n in a c o m p a r a t i v e l y s m a l l a m o u n t of s p a c e . B y p la n tin g t h r e e i n c h e s b y t h r e e i n c h e s in a g r e e n ­ h o u s e b e n c h , f o u r f e e t b y n in e ty f e e t, it w a s p o s s i b l e to r a i s e 2262 p l a n t s . T h is g iv e s a n a d e q u a t e p o p u la tio n f o r a n a l y s i s in a co m p a ra tiv e ly sm a ll sp ace. A co m p lete cro p ro ta tio n c a n be m a d e w ith in th e p e r i o d of t e n w e e k s a n d h e n c e i t w a s p o s s i b l e to o b ta in c o n s i d e r a b l e d a ta . T he p l a n t s w e r e g r o w n u n d e r g r e e n h o u s e c o n d itio n s d u r in g th e p e r i o d f r o m S e p t e m b e r 1951 to M a y 1952 w ith t e m p e r a t u r e f lu c tu a tio n s of 5 0° to 70° F . T h e s e e d l in g s w e r e g e r m i n a t e d in a c o n s ta n t w a t e r l e v e l b e n c h a n d t r a n s p l a n t e d a s s o o n a s p o s s i b l e to m a i n t a i n uni­ f o r m i t y in th e in d iv id u a l p l o t s . S e e d lin g s w e r e p l a n t e d in a g r e e n h o u s e b e n c h c o n ta in in g a s o i l m i x t u r e of a s i l t l o a m w ith m a n u r e a n d p e a t a d d e d . N u tri­ e n t l e v e l s w e r e m a i n t a i n e d b y l iq u id f e e d in g w h e n e v e r th e s o il -14- t e s t s i n d i c a t e d a low l e v e l of n u t r i e n t s . A t t h i s s p a c in g c o m p e t i ti o n b e t w e e n p l a n t s w o u ld b e in ­ t e n s e in l a t e r s t a g e s of g ro w th , m e a s u r e m e n t s w e r e t a k e n w h e n th e r e a c h e d t e n c e n t i m e t e r s in h e ig h t. O th erw ise e n v iro n ­ m e n t a l v a r i a t i o n w i th i n p l o t s a s w e l l a s b e tw e e n p l o t s w o u ld b e s o i n t e n s i f i e d to s u c h a d e g r e e a s to g r e a t l y i n c r e a s e th e e x p e r i ­ m e n ta l e r r o r . T h e fo llo w in g l i n e s w e r e s e l e c t e d f o r t h e s e e x p e r i m e n t s , is a s t r a i n of R o c k w o o d 's P i n k S u p r e m e o r i g i n a l l y s e c u r e d f r o m th e G e o r g e J . B a l l C o m p a n y , W e s t C h ic a g o , I l l i n o i s . P2 i s an i n b r e d i s o l a t e d f r o m th e v a r i e t y H e le n T o b in f r o m th e i n ­ t r o d u c ti o n of D r . H a r o l d W hite of th e U n i v e r s i t y of M a s s a c h u ­ s e tts . T h e s e i n b r e d l i n e s a r e s in g le p l a n t s e l e c t i o n s f r o m t h e s e s t r a i n s a n d h a v e b e e n i n b r e d f o r th e l a s t f iv e g e n e r a t i o n s f r o m w hat w e re a p p a re n tly tru e lin e s. P^ i s a n i n b r e d t h a t d e v e lo p s s lo w ly b u t h a s a l a r g e p r o d u c tio n of d r y w e ig h t a n d i s a v e r y s t u r d y p l a n t. P^, d e v e lo p s r a p i d l y b u t d o e s n o t h a v e a l a r g e a m o u n t of d r y w e ig h t in r e l a t i o n s h i p to i t s s i z e . T h e F^ of t h i s c r o s s is a v e r y v i g o r o u s g ro w in g h y b r i d . It w a s o u ts ta n d in g in t h i s r e s p e c t in a s u r v e y of 350 F^ s n a p d r a g o n s . B . M e a s u r e m e n t s of H e t e r o s i s T o o b ta in e x p e r i m e n t a l e v id e n c e of h e t e r o s i s in A . m a j u s t h r e e e x p e r i m e n t s w e r e c o n d u c te d to o b ta in d a ta on h e ig h t a n d -15- d r y w e i g h t of th e p a r e n t s in th e F p E x p e r i m e n t I w a s c o n d u c te d b y so w in g s e e d D e c e m b e r 1, 1951 a n d on J a n u a r y 15, 1952 t h e s e p l a n t s w e r e b e n c h e d . H e ig h t m e a s u r e m e n t s w e r e t a k e n o n F e b r u a r y 5, 1952. E x p e r i m e n t II - s e e d s w e r e so w n on F e b r u a r y 3, 1952 a n d b e n c h e d on M a r c h 28, 1952. M e a s u r e m e n t s of h e ig h t w e r e t a k e n on A p r i l 6 , 1952. E x p e r i m e n t III - S e e d s w e r e sow n o n M a r c h 28, 1952 a n d on A p r i l 19th t h e s e p l a n t s w e r e b e n c h e d . H e ig h t m e a s u r e m e n t s w e r e t a k e n on M ay 8 , 1952. T h e s a m e p r o c e d u r e w a s f o llo w e d in E x p e r i m e n t s I, II, a n d III. S e e d s of P , P , F , a n d F , w e r e so w n on th e r e s p e c 1 2 1 c* t i v e d a t e s a n d in e a c h e x p e r i m e n t , 350 p l a n t s of P p 1P^, a n d F^ w e r e b e n c h e d b e f o r e th e s e e d l i n g s b e c a m e c r o w d e d in th e p ro p a g a tio n bench. A lo n g w ith t h e h y b r i d a n d th e two p a r e n t s , 1250 p l a n t s of th e F ^ s e g r e g a t i n g p o p u la tio n w e r e b e n c h e d a t th e s a m e t i m e a n d s e l e c t e d a t r a n d o m in o r d e r to a v o i d d i s ­ t o r t i n g th e c u r v e of s e g r e g a t i o n . M e a s u re m e n ts w e re tak en w h e n th e h y b r i d w a s a p p r o x i m a t e l y t e n c e n t i m e t e r s in h e ig h t. T h i s s i z e w a s c h o s e n in o r d e r to a v o id e f f e c t s of o v e r c r o w d ­ in g . C . D r y W eig h t D e t e r m i n a t i o n s D e t e r m i n a t i o n of d r y w e ig h ts of th e P p P 2 a n d F^ p l a n t s w e r e m a d e a f t e r h e ig h t m e a s u r e m e n t s a n d r e s p o n s e to in d o le -16- a c e tic a c id w as re c o rd e d . F r e s h w e ig h ts w e r e t a k e n a n d th e n t h e p l a n t s w e r e p l a c e d in a n o v e n a t 100° C . a n d t h e n d r i e d f o r a p e r i o d of 72 h o u r s . D. R e s p o n s e to In d o le A c e t i c A c id T h e p l a n t s i n E x p e r i m e n t s I, II, a n d III w e r e s p r a y e d w ith in d o le a c e t i c a c i d a f t e r h e ig h t m e a s u r e m e n t s w e r e r e c o r d e d . P l a n t s in E x p e r i m e n t I w e r e s p r a y e d a t 100 p p m . a n d e x h ib ite d t y p i c a l e p i n a s ty . H o w e v e r , it w a s fo u n d t h a t p l a n t s g r o w n in E x p e r i m e n t s II a n d III d u r in g w h ic h th e lig h t i n t e n s i t i e s w e r e h ig h a n d a s t r o n g e r c o n c e n t r a t i o n of in d o le a c e t i c a c i d w a s n e e d e d to p r o d u c e t h e s a m e d e g r e e of r e s p o n s e . A co n c e n tra ­ t i o n of 1000 p p m . o f in d o le a c e t i c a c i d w a s u s e d in t h e s e e x ­ p e rim e n ts . A h a n d a t o m i z e r w a s u s e d in a p p ly in g t h is c h e m i c a l s p r a y w i t h e a c h lo t r e c e i v i n g th e e q u iv a le n t v o lu m e of m a t e r i a l a t th e sa m e co n cen tratio n . O n e - h a l f of th e p l a n t s w e r e le f t u n t r e a t e d and w ere u sed a s c o n tro ls. T h e r e s p o n s e of th e p l a n t s to th e indole a c e t i c a c i d w a s d e t e r m i n e d b y a n a r b i t r a r y s t a n d a r d u s ­ in g th e n u m b e r s 0 - 5 to d e s ig n a te th e d e g r e e of e p i n a s t y w it h th e h i g h e r n u m b e r sh o w in g th e g r e a t e s t e p i n a s ty a n d th e lo w e s t n u m b e r sh o w in g no e p i n a s t y . T h e d e g r e e of e p i n a s t y w a s r e c o r d e d a s s o o n a s t h e r e w a s a d i f f e r e n c e b e t w e e n th e i n b r e d s a n d th e h y b r i d s . -17- In o r d e r to d e t e r m i n e if a c o r r e l a t i o n e x i s t e d b e t w e e n h e ig h t a n d e p i n a s t i c r e s p o n s e p l a n t s w e r e r e c o r d e d a n d i d e n ­ t i f i e d in s u c h a m a n n e r t h a t a c o m p a r i s o n of h e ig h t a n d e p i n a s t y c o u ld b e m a d e f o r e a c h i n d iv id u a l p la n t . E . B io lo g ic a l T e s ts To d e t e r m i n e th e p r e s e n c e of a n i n h i b i t o r o r a n i n a c t i v a ­ t o r in th e i n b r e d s a b i o lo g i c a l t e s t w a s e m p lo y e d . A la m e rc e ry ( l ) h a s sh o w n t h a t c u c u m b e r s e e d l i n g s a r e v e r y s e n s i t i v e to in d o le a c e t i c a c i d in t h e i r r e s p o n s e to g e r m i n a t i o n a n d g r o w th of h y p o c o ty l a n d r o o t s . W hen s e e d s a r e g ro w n in a s o lu tio n of in d o le a c e t i c a c id , t h e a m o u n t of r o o t g r o w th i n h ib itio n i s in p r o p o r t i o n to th e c o n c e n t r a t i o n of in d o le a c e t i c a c i d . Hence, t h i s m e th o d w a s u s e d to d e t e r m i n e th e p r e s e n c e of a n in h i b i t o r o r i n a c t i v a t o r of in d o le a c e t i c a c i d . In o r d e r to d e t e r m i n e w h e t h e r o r n o t a n i n h i b i t o r o r a n i n a c t i v a t o r w a s p r e s e n t , t e n g r a m s of p l a n t m a t e r i a l f r o m th e t o p s of P j , P £ , a n d w e r e m a c e r a t e d in a w a r i n g b l e n d o r a n d m a d e up to a v o lu m e of 100 c c . b y u s in g d i s t i l l e d w a t e r . To t h i s s l u r r y , in d o le a c e t i c a c i d w a s a d d e d to m a k e a f in a l c o n c e n t r a t i o n of 25 p p m . S ix te e n c u c u m b e r s e e d l i n g s w e r e p l a c e d on a f i l t e r p a p e r in a p e t r i d ish , a n d f iv e c u b ic c e n t i ­ m e t e r s of t h i s s l u r r y w a s a d d e d to e a c h p e t r i d i s h . In a d d i­ t i o n a d i s t i l l e d v a t e r s o lu tio n of in d o le a c e t i c a c i d a t 25 p p m . an d d is tille d w a te r alo n e w e re u s e d a s c o n tro ls . Each tre a t- -18- m ent w as re p lic a te d th re e tim e s . The cu c u m b e r se e d lin g s w e r e a l l o w e d to g e r m i n a t e u n d e r a c o n t r o l l e d t e m p e r a t u r e , b o t h i n c o n s ta n t lig h t a n d in d a r k n e s s . A p p ro x im a te ly four d a y s a f t e r t r e a t m e n t r o o t m e a s u r e m e n t s in n d i l l i m e t e r s w e r e • t a k e n a s w e l l a s p e r c e n t a g e of g e r m i n a ti o n . S in c e a s i g n i f i ­ c a n t d i f f e r e n c e w a s fo u n d th e l o c a l i z a t i o n of t h e i n a c t i v a t o r w as a tte m p te d . In a n a t t e m p t to l o c a l i z e th e a c t i v e p r i n c i p l e p l a n t s w e r e d iv id e d in to two l o t s b e f o r e b e in g m a c e r a t e d in a w a r i n g b le n d o r. M e ris te m a tic tis s u e w as s e p a ra te d fro m o ld er t i s s u e a n d th e s a m p l e s w e r e p r e p a r e d s e p a r a t e l y a n d m a d e up to e q u iv a le n t c o n c e n t r a t i o n s . ,F . E f f e c t of L i g h t I n t e n s i t y To d e t e r m i n e th e e f f e c t of lig h t i n t e n s i t y on th e r e s p o n s e of s n a p d r a g o n s to in d o le a c e t i c a c id , 1200 p la n t s e a c h of F^, p ., and 1 w ere used. O n e - h a l f of t h e s e p l a n t s w e r e g ro w n “ in a.n o p e n b e n c h r e c e i v i n g f u ll lig h t a n d o n e - h a l f w e r e g ro w n under a ch eeseclo th shade. K r o n e a n d B u l m e r (28) h a v e sh o w n t h a t c h e e s e c l o t h s h a d e r e d u c e s s o l a r r a d i a t i o n b y a p ­ p ro x im a te ly 45% . In e a c h p lo t 400 p l a n ts w e r e t r e a t e d w ith in d o le a c e t i c a c i d a f t e r g ro w in g u n d e r t h e s e c o n d itio n s f o r a p e r i o d of t h r e e w e e k s . A f t e r t r e a t m e n t o n e - h a l f of th e t r e a t e d p l a n t s in e a c h plot w e r e s h if t e d to th e o t h e r e n v i r o n ­ m en t. -19- T o d e t e r m i n e t h e e f f e c t of lig h t i n t e n s i t y o n th e g r o w th o f i n b r e d s a n d h y b r i d a c o n t r o l p l o t of P , , P ^ and F ^ 1 con- t a in i n g 200 p l a n t s e a c h w e r e g ro w n u n d e r e a c h of th e a b o v e lig h t c o n d itio n s . The c o n tro l p lo ts re m a in e d u n d er the o r i g i ­ n a l e n v i r o n m e n t a l c o n d itio n s t h r o u g h o u t th e e x p e r i m e n t . G . S o l a r R a d ia t io n S o l a r r a d i a t i o n m e a s u r e m e n t s w e r e o b ta in e d f r o m th e U n ite d S t a t e s D e p a r t m e n t of A g r i c u l t u r e H y d r o lo g ic S ta tio n a t M ic h ig a n S ta te C o lle g e , E a s t L a n s in g , M ic h ig a n . M ea­ s u r e m e n t s w e r e in g r a m c a l o r i e s p er s q u a r e c e n t i m e t e r . C r a b b (10, 11) s h o w s, g r a m c a l o r i e s p e r s q u a r e c e n t i m e t e r is d i r e c t l y p r o p o r t i o n a l to fo o t c a n d le s a s a m e a s u r e m e n t c£ lig h t i n t e n s i t y . -20- RESULTS I. H e t e r o s i s In E x p e r i m e n t I h e t e r o s i s w a s sh o w n to e x i s t w h e n A . m a j u s w a s g ro w n f r o m D e c e m b e r 1, 1951 t h r o u g h F e b r u a r y 5, 1952. ( F i g u r e I). d id s u r p a s s L P ^ . T h e h y b r i d d id n o t s u r p a s s th e but T h e h y b r i d w a s . 73 c e n t i m e t e r s s u p e r i o r in h e ig h t to th e m i d - p a r e n t m e a n . ( T a b le l) . T h e h y b r i d s h o w s a s u p e r i o r i t y in d r y w e ig h t o v e r e i t h e r o f th e p a r e n t s a n d a n i n c r e a s e of . 1 1 5 g r a m s o v e r th e m id -p a re n t m ean. (T a b le 2). T h e s e g r e g a t i n g p o p u la tio n ( F 2) a s sh o w n in T a b le 1 h a s a w id e r a n g e of v i g o r ; s o m e of th e p l a n t s b e in g s m a l l e r t h a n e i t h e r of th e p a r e n t s b u t none of t h e m s u r p a s s i n g t h e h y b r i d . p e c t e d in a s e g r e g a t i n g T h is is w h a t i s n o r m a l l y e x ­ p o p u la tio n . H e te ro s is w as still d i s p l a y e d due to th e f a c t th a t th e h y b r i d w a s s u p e r i o r to th e m id -p a re n t m ean. A n i n c r e a s e in t h e a m o u n t of h e t e r o s i s a s sh o w n in F i g ­ u r e II a n d T a b le 2 w a s found in E x p e r i m e n t II. The h y b rid s u r p a s s e d b o th of th e p a r e n t s in h e ig h t a n d in d r y w e ig h t h a v in g a n i n c r e a s e o v e r th e m i d - p a r e n t m e a n of 3 .6 5 c e n ­ t i m e t e r s p e r p la n t, a n d . 354 g r a m s p e r p l a n t . -21- TABLE 1 A v e r a g e h e ig h t in c e n t i m e t e r s of 350 p l a n t s e a c h of i n b r e d (P^ a n d P 2 ) a n d th e h y b r i d (F^) a n d s e g r e g a t i n g p o p u la tio n (F ^ ) of A . m a j u s . P a r e n t 1 P a r e n t 2 M i d - p a r e n t H y b r id H etero sis* (F 2> m e a n (* V (p i> (p 2 > E x p I ** 7 .3 E x p II*** S. 9 E x p III 4. 7 ' 9 .6 5 10. 38 7.91 0. 73 8 . 93 7 .4 1 5 11 . 1 9 .9 3 .6 5 9 .2 6 . 95 1 0 .9 6 .9 3. 95 12 * H e t e r o s i s i s th e d i f f e r e n c e b e tw e e n m i d - p a r e n t m e a n a n d F^. ** D e c e m b e r 1, 1951 th r o u g h F e b r u a r y 5, 1952. *** F e b r u a r y 3, 1952 t h r o u g h A p r i l 6 , 1952. ❖❖❖^March 28, 1952 t h r o u g h M a y 8 , 1952. -22- TABLE 2 A v e r a g e d r y w e ig h t in g r a m s of in d iv id u a l p l a n t s of P a r e n t 1 ( P .) P a r e n t 2 ( P ) a n d h y b r i d (F ). ^ JL M I n d iv id u a l a v e r a g e s a r e b a s e d on th e a v e r a g e of 350 p l a n t s . P a r e n t 1 P a r e n t 2 M i d - p a r e n t H y b r id m ean ( P 2) (p i> ( F i> E x p I** H etero sis* 0.216 0. 357 0 .2 8 6 0 .4 0 1 0. 115 E x p II*** 0 .2 3 1 0 . 206 0 .2 1 6 0. 570 0. 354 sic*** E x p III 0. 12 0 . 16 0. 14 0.6 0 .4 6 * H e t e r o s i s i s th e d i f f e r e n c e of th e f r o m th e m i d - p a r e n t m e a n . ** D e c e m b e r 1, 1951 t h r o u g h F e b r u a r y 5, 1952. *** F e b r u a r y 3, 1952 th r o u g h A p r i l 6 , 1952. * * * * M a r c h 28, 1952 t h r o u g h M a y 8 , 1952. F ig u re I C o m p a r i s o n of h e ig h t a n d f r e q u e n c y of P^> Pg, F j an d F ^ i l l u s t r a t i n g h e t e r o s i s in A . m a ju s w ith th e n o r m a l s e g r e g a t i o n in th e F 2 * -23- EXPERIMENT I 120 MID-PARENT MEAN 100 80 2 60 40 68 20 J L MEAN FREQUENCY F, 60 40 20 J L - — HETEROSIS (.73 cm.) I I 2 3 4 5 6 7 8 9 10 II 12 13 HEIGHT IN CENTIMETERS Figure I 1 14 M 15 16 I 17 I I 18 19 20 F ig u re II C o m p a r i s o n of h e ig h t a n d f r e q u e n c y of Pf, P 2, F a n d F i l l u s t r a t i n g h e t e r o s i s in 1 2 A . m a j u s w ith th e n o r m a l s e g r e g a t i o n in -24- EXPERIMENT IE MID-PARENT MEAN 99993 100 80 55 60 40 20 51 0 F. MEA 60 > o |O 40 K u. 20 0 HETEROSIS ( 9 .6 5 cm.) 60 60 40 20 0 6 7 8 9 10 HEIGHT IN CENTIMETERS Fi g u r e II 11 12 13 14 15 16 -25- T h e F ^ a g a i n s h o w e d a w id e r a n g e of v ig o r w ith s o m e cf t h e p o p u la tio n b e in g l e s s v ig o r o u s th a n eith er of the p a r e n t s a n d w ith n o n e of th e in d iv id u a ls s u r p a s s i n g th e h y b r id . T he h e t e r o s i s in E x p e r i m e n t II b o th a s to h e ig h t a n d d r y w e ig h t i s g r e a t e r t h a n in E x p e r i m e n t I. H e t e r o s i s w a s a g a in d is p la y e d w ith th e h y b r id s u r p a s s i n g b o th of th e p a r e n t s in E x p e r i m e n t III. A s show n in F i g u r e III a n d T a b le s 1 a n d 2 th e i n c r e a s e in h e ig h t p e r p l a n t of th e h y ­ b r i d s o v e r th e m i d - p a r e n t m e a n w a s 3 .9 5 c e n t i m e t e r s . The i n c r e a s e in d r y w e ig h t p e r p la n t of th e h y b r id s o v e r m i d ­ p a r e n t m e a n w a s .4 6 g r a m s . E x p e r i m e n t III sh o w e d a c o n ­ s i d e r a b l e i n c r e a s e of h e t e r o s i s b y b o th c r i t e r i a o v e r th e two p r e c e d i n g e x p e r i m e n t s . A n i l l u s t r a t i o n of th e d if f e r e n c e b e ­ tw e e n P^, P £ a n d F^ c a n b e s e e n in F i g u r e s IV a n d V. II. P h y s i o l o g i c a l R e s p o n s e / A . P h y s i o l o g i c a l R e s p o n s e to In d o le A c e t i c A c id It w a s found in p r e l i m i n a r y e x p e r i m e n t s t h a t th e h y b r id e x h ib ite d a n e p i n a s ti c r e s p o n s e to c o n c e n t r a t i o n s of in d o le a c e t i c a c i d a s low a s 5 p p m . T h e p a r e n t s e x h ib ite d l i t t l e o r no r e s p o n s e a t t h is c o n c e n t r a t i o n . F u r th e r in v estig atio n s p r o v e d t h a t th e h y b r i d s e x h ib ite d a g r e a t e r r e s p o n s e to i n ­ d o le a c e t i c a c i d t h a n e i t h e r of th e p a r e n t s . ( F i g u r e VI). F i g u r e HI C o m p a r i s o n of h e ig h t a n d f r e q u e n c y of an<* i l l u s t r a t i n g h e t e r o s i s in m a j u s w ith th e n o r m a l s e g r e g a t i o n in th e -26- EXPERIM ENT H £ MID-PARENT MEAN FREQUENCY F, MEAN sret v -HETEROSIS- (3.95 cm) 5 6 7 8 9 10 HEIGHT IN CENTIMETERS Figure III II -27- F i g u r e IV A v iew of c u l t u r e s sho w in g u n i f o r m i t y of in f o r e g r o u n d , cen te r, background. -28- F ig u re V T h e e f f e c t of H e t e r o s i s on th e g r o w th of A. m a j u s . r ig h t a r e P p T h e p l a n ts r e a d i n g f r o m le f t to P^, a n d th e h y b r id F p -29- T h i s p h e n o m e n a w a s m o re , p r o n o u n c e d in th e f a l l a n d w i n t e r t h a n i n th e s p r i n g a s i s e v id e n t b y th e f a c t t h a t th e c o n c e n t r a ­ t i o n s h a d to b e i n c r e a s e d in E x p e r i m e n t s II a n d HI f r o m 100 p p m . to 1000 p p m . to o b ta in th e s a m e r e s p o n s e a s i n E x p e r i ­ m e n t I. I m m e d i a t e l y a f t e r t r e a t m e n t w ith 1000 p p m . in d o le a c e t i c a c i d , b o th th e h y b r i d a n d th e i n b r e d s s h o w e d th e s a m e resp o n se. T he in b re d s r e c o v e r e d f r o m th is ep in a sty m o re r a p i d l y th a n th e h y b r i d . E p i n a s t i c r e s p o n s e w a s e v a lu a t e d a p p r o x i m a t e l y 72 h o u r s a f t e r t r e a t m e n t w h e n t h e r e w a s a c o n s i s t e n t d i f f e r e n c e b e t w e e n th e i n b r e d s a n d th e h y b r i d s . E p i n a s t i c r e s p o n s e of th e h y b r i d s e x c e e d e d t h a t of the p a r e n t s c o n s i s t e n t l y in a l l t h r e e e x p e r i m e n t s (T a b le 3). As sh o w n l a t e r , th e r a t e of r e c o v e r y in b o th h y b r id a n d p a r e n t s i s d e p e n d e n t up o n l ig h t i n t e n s i t y . A n F 2 p o p u la tio n w a s t r e a t e d in e a c h of t h e s e e x p e r i m e n t s to r e c o r d th e n a t u r e of th e s e g r e g a t i o n . M e a s u re m e n ts in d ic a te d a f a ir c o r re la tio n b e t w e e n s i z e of p l a n t a n d d e g r e e of e p i n a s t y . (See A p p e n ­ dix) . B e c a u s e v i g o r a n d r e s p o n s e to in d o le a c e t i c a c i d a p ­ p e a r e d to b e a s s o c i a t e d , h e ig h t a n d e p i n a s t y of e a c h i n d i ­ v i d u a l in th e F 2 s e g r e g a t i n g p o p u la tio n w e r e r e c o r d e d so t h a t th e e x t e n t of c o r r e l a t i o n m ig h t be d e t e r m i n e d . T h e r e l a t i o n s h i p b e tw e e n th e r e s p o n s e to in d o le a c e t i c a c i d a n d h e ig h t w a s d e t e r m i n e d a n d no s ig n i f ic a n t c o r r e l a ­ t i o n w a s o b t a in e d i n E x p e r i m e n t I u n d e r low lig h t i n t e n s i t y . -30- F i g u r e VI T h e e f f e c t of ind ole a c e t i c a c i d on th e g r o w th of i n b r e d a n d h y b r id p la n ts of A. m a j u s . T h e p la n t s on the le ft in e a c h g ro u p w e r e le ft u n t r e a t e d . T h e plants on the r ig h t w e r e t r e a t e d w ith in d o le a c e t i c a c i d a t 1000 p p m . le ft P ^ , c e n t e r P^, rig h t F ^ G ro u p a t -31- TABLE 3 E p i n a s t i c r e s p o n s e of P a r e n t 1 ( P ^ , P a r e n t 2 ( P 2) and h y b r i d (F^) to t r e a t m e n t w i t h in d o le a c e t i c a c i d . P arent 1 (p i) P aren t 2 CP2 ) H y b rid (p i) Exp I 2 1 3 E x p II 2 1 4 E x p III 1 1 3 D e g r e e of e p i n a s t y 0 - no e p i n a s t y 1 - v e r y s li g h t e p i n a s t y 2 - m o d e ra te e p in a s ty 3 - h ig h e p i n a s t y 4 - v e r y h ig h e p i n a s t y T h e e p i n a s t y w a s m e a s u r e d b y th e a m o u n t of c u r l in g a n d d i s t o r t i o n of th e l e a f . a fte r tre a tm e n t. M e a s u r e m e n t s w e r e t a k e n 72 h o u r s R esp o n se im m e d ia te ly a fte r tre a tm e n t w as v e r y h ig h o n b o th p a r e n t s a n d th e h y b r id . -32- In E x p e r i m e n t II a c o r r e l a t i o n of . 0738 w a s fo u n d w h ic h w a s s i g n i f i c a n t to th e 5% l e v e l . T h is e x p e r i m e n t w a s c o n d u c te d u n d e r m o d e r a t e lig h t i n t e n s i t i e s . In E x p e r i m e n t III a c o r r e ­ la tio n of .4 2 0 6 w a s fo un d a n d t h i s w a s s ig n i f i c a n t to th e le v e l. 1% A h ig h d e g r e e of c o r r e l a t i o n w a s n o t a n t i c i p a t e d s in c e t h e r e w a s a n o v e r l a p p i n g of th e p a r e n t s a n d th e h y b r i d s in h e i g h t a s sh o w n in F i g u r e I, II a n d III. T h e r e s p o n s e of th e F 2 to in d o le a c e t i c a c i d c o u ld b e c o r r e l a t e d w ith h e ig h t s i n c e m o s t of th e p l a n t s h a v in g a h ig h d e g r e e of e p in a s ty w e r e in th e l a r g e r s i z e c l a s s e s a n d th e p l a n t s sho w ing th e l e a s t e p i n a s t y w e r e t h e p l a n t s in th e s m a l l e r s iz e c l a s s e s a s sh o w n i n th e t a b l e s o n h e ig h t c o r r e l a t i o n in th e A p p e n d ix . T h i s i n d i c a t e s t h a t th e p l a n t s in th e s e g r e g a t i n g p o p u la tio n sh o w in g th e h i g h e s t d e g r e e of r e s p o n s e a r e of th e h y b r i d g e n o ty p e . T h e p l a n t s sh o w in g th e l e a s t r e s p o n s e a n d th e l e a s t h e ig h t a r e p r e s u m a b l y n e a r e r th e p a r e n t a l g e n o ty p e s . B. B io lo g ical T e s ts S in c e t h e F^ c o n s i s t e n t l y sh o w e d m o r e e p i n a s t y i n r e s p o n s e to in d o le a c e t i c a c i d th a n e i t h e r of th e p a r e n t s , it w a s f i r s t th o u g h t t h a t t h i s d i f f e r e n c e w a s due to a g r e a t e r p r o d u c t i o n of g r o w t h s u b s t a n c e s in th e h y b r i d s , a n d h e n c e b y th e a d d i t i o n of a n in d o le a c e t i c a c i d s p r a y , th e h y b r i d s ' p h y to to x ic t h r e s h h o l d w o u ld b e r e a c h e d s o o n e r th a n th e i n b r e d s . It w a s fo u n d b y c h e m i c a l a n a l y s i s t h a t no d i f f e r e n c e s in in d o le a c e t i c a c i d -33- c o u ld b e d e m o n s t r a t e d b e t w e e n i n b r e d s a n d h y b r i d s . S in ce t h e h y b r i d s p r o d u c e d m o r e g r o w th it w a s b e l i e v e d t h a t th e in d o le a c e t i c a c i d in th e h y b r i d s w a s b e in g u t i l i z e d f o r g r o w th m o r e e f f i c i e n t l y w h ile in th e i n b r e d s i t s e f f ic ie n c y w a s r e ­ d u c e d p e rh a p s by a n in h ib ito r o r an in a c tiv a to r. It w a s fo u n d b y u s i n g th e c u c u m b e r s e e d l i n g s t e s t to d e ­ t e r m i n e th e p r e s e n c e o f a n in h i b i t o r o r a n the i n b r e d s or and in a c tiv a to r th at h a d s o m e m e c h a n i s m of b r e a k i n g dow n o r i n a c t i v a t i n g in d o le a c e t i c a c id . ( T a b le 4). The s e e d l i n g s c o n ta in in g a n e x t r a c t o f P^ a n d P 2 p l u s in d o le a c e t i c a c i d a p p r o a c h e d in s i z e th e s e e d l i n g s g e r m i n a t e d in d istille d w a te r. O n t h e o t h e r h a n d a s c o n t r a s t e d to th e i n h i b i t e d g r o w th w h e r e s e e d l i n g s w e r e g r o w n i n a s o lu tio n o f in d o le a c e t i c a c i d w a s th e c u c u m b e r s e e d l i n g s g r o w in g in th e e x t r a c t o f th e h y b r i d a n d in d o le a c e t i c a c i d r e s p o n d e d in a s i m i l a r m a n n e r to th e s e e d l in g s g e r m i n a t e d in in d o le a c e t i c a c i d s o lu tio n , i n d ic a tin g l i t t l e b r e a k d o w n of in d o le a c e t i c a c i d w h e r e th e h y b r i d e x t r a c t w a s u s e d . F i g u r e V II). ( T a b le 4, T h e s e e d l i n g s g e r m i n a t e d in th e d a r k sh o w a g r e a t e r r e s p o n s e to i n d o le a c e t i c a c i d th a n t h o s e g e r m i n a t e d in th e lig h t; a f u r t h e r i n d i c a t i o n th a t lig h t is a f a c t o r . ( T a b le 4 a n d 5). It w a s fo un d b y u s in g t h e c u c u m b e r s e e d lin g t e s t t h a t th e i n b r e d s in th e s o lu ti o n of in d o le a c e t i c a c i d a p p r o a c h e d th e d i s t i l l e d w a t e r c o n t r o l s . T h e h y b r i d in th e s o lu tio n of -34- TABLE 4 E f f e c t of a s i m u l t a n e o u s a p p l i c a t i o n of a n a q u e o u s e x t r a c t of e i t h e r P ^ o r o r F^ a n d in d o le a c e t i c a c i d a t 25 p p m . on g e r m i n a t i o n a n d r o o t g r o w t h of c u c u m b e r s e e d l i n g s . T re a tm e n t I R o o t g r o w t h in m m . A v e . 16 se e d lin g s II R o o t g r o w th in m m . A v e . 16 s e e d l in g s A verage D istille d W ater 5 .8 5. 5 5 .2 IAA* 0 .4 9 1.0 0. 74 P arent 1 + 25 p p m . IAA* 1 .9 5 2. 33 2. 14 P arent 2 + 25 p p m . IAA* 3. 7 4. 3 4 . 00 H y b r i d 4* 25 p p m . IAA* .4 7 . 56 S e e d l i n g s g e r m i n a t e d in d a r k * in d o le a c e t i c a c i d .5 1 -35- TABLE 5 E f f e c t of a s i m u l t a n e o u s a p p l i c a t i o n of a n a q u e o u s e x t r a c t o f e i t h e r P^ o r o r F-^ a n d in d o le a c e t i c a c i d a t 25 p p m . on g e r m i n a t i o n a n d r o o t g r o w t h of c u c u m b e r s e e d l i n g s . T re a tm e n t ................I .... — " R o o t g r o w t h in m m . A v e . 16 S e e d lin g s D istille d W ater IAA* P arent 1 + 25 p p m . IAA* P aren t 2 + 25 p p m . IAA* H y b rid + 25 p p m . IAA* 5. 1 II R o o t g r o w th in m m . A v e . 16 S e e d lin g s 4. 95 5 .0 2 .8 4 1. 09 .9 6 1. 35 1 .5 1 1 .4 3 2 .9 9 3. 94 3. 31 . 72 .5 1 . 61 S e e d l i n g s g e r m i n a t e d in lig h t * in d o le a c e t i c a c i d A verage -36- i n d o le a c e t i c a c i d w a s c o m p a r a b l e to th e in d o le a c e t i c a c i d c o n tro l. ( F i g u r e V II). T h i s i n d i c a t e s t h a t th e i n b r e d s h a v e s o m e m e c h a n i s m f o r i n a c ti v a t i n g o r f r e a k i n g down in d o le a c e t i c a c i d to a m u c h g r e a t e r e x te n t t h a n th e h y b r id . T h i s w ill h e lp e x p l a in w h y th e i n b r e d s r e c o v e r f r o m t h e e p i n a s t y w h e n t r e a t e d w ith in d o le a c e t i c a c i d m o r e r a p i d ­ l y t h a n th e h y b r i d s . T o d e t e r m i n e i n w h a t p o r t i o n o f th e p la n t the in h ib ito r o r in a c tiv a to r w as lo c a liz e d o r m o st a c ­ tiv e , e x t r a c t s w e r e m a d e of y ou ng m e r i s t e m a t i c t i s s u e a s w e l l a s e x t r a c t s of m a t u r e t i s s u e . T h e re is m o re in a c tiv a ­ t i o n of in d o le a c e t i c a c i d in th e m e r i s t e m a t i c t i s s u e th a n in the m a t u r e t i s s u e . ( T a b l e 6). H I. L i g h t I n t e n s i t y O b s e r v a t i o n s A . E f f e c t of L i g h t on H e t e r o s i s S in c e a p r o g r e s s i v e i n c r e a s e in h e t e r o s i s w a s fo u n d in s u c c e s s i v e e x p e r i m e n t s a s t h e s e a s o n a d v a n c e d tw o c u r v e s w e r e p l o t t e d to sh o w th e c o n c u r r e n t v a r i a t i o n in h e t e r o s i s an d s o la r ra d ia tio n . ( F i g u r e V III). T h e s o l a r r a d i a t i o n d a ta w e r e o b t a i n e d f r o m th e U n ite d S ta t e s D e p a r t m e n t of A g r i c u l ­ t u r e , H y d r o lo g ic R e s e a r c h S ta tio n , M ic h ig a n S ta te C o lle g e , E a s t L a n s i n g , M ic h ig a n a n d i t w a s fou nd t h a t th e s o l a r r a d i a ­ ti o n i n c r e a s e d s t e a d i l y f r o m J a n u a r y th r o u g h M ay 1952. ( F i g u r e VIII). -37- ?£- C j O I iA : T > , r i » ^ > < * v * ' t u n ( - . ' - ' ^ * F i g u r e VII T h e e f fe c t of s im u l t a n e o u s a p p l ic a t i o n of a n a q u e o u s e x t r a c t of s n a p d r a g o n a n d in d o le a c e t i c a c i d a t 25 p p m . on th e g e r m i n a t i o n a n d r o o t g r o w th of c u c u m b e r s e e d lin g s F r o m top to b o tto m , 1. d i s t i l l e d w a t e r , 2. in d o le a c e t i c a c i d a t 25 p p m . , 3. a q u e o u s e x t r a c t of a c i d a t 25 p p m . , 4. a q u e o u s e x t r a c t of P 1 + ind ole a c e t i c a c i d a t 25 p p m . , 5. a q u e o u s e x t r a c t of a c i d a t 25 pp m . + in d o le a c e t i c + in d o le a c e t i c • ’ * -36- TABLE 6 E f f e c t of a n a q u e o u s e x t r a c t of m e r i s t e m a t i c t i s s u e a n d o f d i f f e r e n t i a t e d t i s s u e o f P^, p ^ a n d F^ t o g e t h e r w ith in d o le • a c e tic a c i d a t 25 p p m . on g e r m i n a t i o n s a n d r o o t g r o w th of c u c u m b e r s e e d lin g s . T re a tm e n t I R o o t g r o w th in m m . A ve. 15 s e e d l i n g s II R o o t g r o w th in m m . A v e . 15 s e e d l i n g s III R o o t g r o w th in m m . A v e . 15 s e e d lin g s A verage D istille d W ater 5 3 .6 61.8 64. 8 60. 1 IAA* 12 . 6 9 .0 13. 9 11.8 P i m e ris te ­ m a tic tis s u e + IAA* 2 9 .4 3 5 .6 34. 3 33. 1 d iffe re n ­ tia te d tissu e + IAA* 17. 1 28. 0 3 2 .2 25. 7 P 2 m e ris te ­ m atic tis s u e + IAA* 5 0 .4 54. 7 56. 5 5 3 .8 d iffe re n ­ tia te d tiss u e + IAA* 18. 1 17. 8 3 0 .4 21.8 24. 0 38. 1 4 2. 0 34. 6 21. 0 9. 1 55. 1 28. 3 F j m e ris te ­ m atic tis s u e + IAA* d iffe re n ­ tia te d tissu e + IAA* S e e d lin g s g e r m i n a t e d in lig h t * in d o le a c e t i c a c i d F i g u r e VIII I n c r e a s e i n s o l a r r a d i a t i o n in g r a m c a l o ­ r i e s p e r s q u a r e c e n t i m e t e r s f r o m D e c e m b e r 1, 1951 th r o u g h M a y 15, 1952 a t E a s t L a n s i n g , M ic h ig a n . -39- 1------ 400 350 AVERAGE SOLAR RADIATION GRAM / CALORIES PER SQUARE CENTIM ETER 450 300 250 200 - 150 100 50 _L DEC. JAN. FEB. MAR. APR. MONTHLY AVERAGES OF SOLAR RADIATION F i g u r e VI II MAY -40- In D e c e m b e r t h e t o t a l s o l a r r a d i a t i o n w a s a l i t t l e l e s s t h a n 100 g r a m c a l o r i e s p e r s q u a r e c e n t i m e t e r a n d s t e a d i l y i n c r e a s e d to a p p r o a c h a s t r a i g h t lin e r e a c h i n g i t s m a x i m u m of a p p r o x i m a t e l y 400 g r a m c a l o r i e s p e r s q u a r e c e n t i m e t e r f o r t h i s e x p e r i m e n t in M a y . T h e i n c r e a s e in h e ig h t of th e h y b r i d s o v e r th e p a r e n t s is p l o t t e d a g a i n s t s o l a r r a d i a t i o n d u r in g E x p e r i m e n t s I, II, a n d III. lin e . ( F i g u r e IX ). The r e s u lt is v e ry n e a rly a s tra ig h t A s th e s o l a r r a d i a t i o n i n c r e a s e d th e d e g r e e of h e t e r o - s is in c re a s e d . S o l a r r a d i a t i o n w a s p l o t te d a g a i n s t th e d r y w e ig h t i n ­ c r e a s e of th e i n E x p e r i m e n t I, II, a n d III, a n d t h i s a g a i n g a v e a l m o s t a s t r a i g h t lin e c o r r e l a t i o n . ( F i g u r e IX ). As t h e s o l a r r a d i a t i o n i n c r e a s e d , th e d i f f e r e n c e in d r y w e ig h t b etw een p a r e n ts and h y b rid in c r e a s e d . B o th h e ig h t a n d d r y w e ig h t m e a s u r e m e n t s of h e t e r o s i s g a v e a l m o s t a p e r f e c t c o r r e l a t i o n w i t h i n c r e a s e in s o l a r r a d i a t i o n a s sh o w n b y th e l in e a r ity of the c u r v e s . T h e f a c t t h a t th e s lo p e s of t h e two c u r v e s a r e a l m o s t i d e n t i c a l i s e v id e n c e of a t h r e e w a y c o r r e l a t i o n b e tw e e n h e ig h t, a m o u n t of d r y w e ig h t a n d s o l a r r a d i a t i o n . It w a s fo u n d t h a t w h e n th e i n b r e d s a n d h y b r i d w e r e r a i s e d u n d e r th e s a m e e n v i r o n m e n t a l c o n d itio n s w ith th e e x c e p t i o n of lig h t i n t e n s i t y t h a t th e i n b r e d s u n d e r low lig h t i n t e n s i t y w e r e s i m i l a r to th e h y b r i d in s i z e . U n d e r h ig h 400 EXPERIMENT I f f 350 300 H eight I n c r e a s e Dry W eight I n c r e a s e 250 EXPERIMENT I I 200 150 AVERAGE SOLAR RADIATION GRAM/CALORIES PER SQUARE CENTIMETER -41- 100 E X P ER IM EN T X 50 INCREASE OF F, OVER P, AND Pt F i g u r e IX R e l a t i o n s h i p of th e i n c r e a s e in h e ig h t a n d d r y w e ig h t of h e t e r o s i s to s o l a r r a d i a t i o n . TABLE 7 S o l a r r a d i a t i o n in r e l a t i o n to h e t e r o s i s of A . m a j u s . D ays G row n T o tal s o la r ra d ia tio n rec e iv e d E x p I* 62 5 5 1 2 .9 88. 9 . 115 . 73 E x p II** 58 1 3 4 3 3 .8 2 3 1 .6 . 354 3 .6 5 E x p III*** 40 1 6 0 1 8 .1 400. 4 .4 6 3. 95 A v e . d a ily H etero sis s o la r A ve. d ry A v e .h t. ra d ia tio n w t. i n in c re a se c r e a s e F^ F^ * S e e d s s o w n D e c e m b e r 1, g e r m i n a t e d D e c e m b e r 6, h a r v e s t e d F e b r u a r y 5, 1952. ** S e e d s s o w n F e b r u a r y 8 , 1952, g e r m i n a t e d F e b r u a r y 13, 1952, h a r v e s t e d A p r i l 6 , 1952. *** S e e d s so w n A p r i l 3, 1952, g e r m i n a t e d A p r i l 8 , 1952, h a r ­ v e s t e d M a y 12, 1952. jS:*** H e t e r o s i s d e t e r m i n e d b y th e i n c r e a s e of th e F^ o v e r th e m id -p a re n t m ean. -4 3 - l ig h t i n t e n s i t y th e i n b r e d s w e r e c o n s i d e r a b l y i n f e r i o r to th e h y b r i d in s i z e . ( F i g u r e X). T h is a g a i n i n d i c a t e s t h a t s o l a r r a d i a t i o n in f lu e n c e s h e t e r o s i s in A . m a j u s . B. E f f e c t of lig h t on th e p h y s io l o g i c a l r e s p o n s e to i n ­ d o le a c e t i c a c i d T r e a t m e n t of p l a n t s in th e f a ll a n d w i n t e r , w h e n n a t u r a l lig h t is v e r y low, g a v e r e s p o n s e to in d o le a c e t i c a c i d in c o n ­ c e n t r a t i o n s a s low a s 5 p p m . A s th e lig h t i n t e n s i t y i n c r e a s e d d u r in g th e s p r i n g th e c o n c e n t r a t i o n s h a d to b e r a i s e d f r o m 100 to 1000 p p m . to o b ta in th e s a m e r e s p o n s e . T h is in d ic a te s t h a t t h i s r e a c t i o n i s a p h o t o c h e m i c a l o ne. It w a s fo u n d t h a t th e p a r e n t s r e c o v e r e d f a s t e r th a n th e h y b r i d a n d in e a c h c a s e lig h t r e c e i v e d a f t e r t r e a t m e n t h a d a m o r e p r o f o u n d e f f e c t o n r e c o v e r y th a n th e lig h t r e c e i v e d b e ­ fo re tre a tm e n t. ( F i g u r e s V a n d X l). H ig h lig h t a f t e r t r e a t * m e n t g r e a t l y a c c e l e r a t e d r e c o v e r y on a l l t h r e e l i n e s a n d on p l a n t s t h a t h a d b e e n g r o w n u n d e r e i t h e r h ig h o r low lig h t. F i g u r e XII i l l u s t r a t e s th e p h y s i o l o g i c a l r e p o n s e of th e i n b r e d a n d h y b r id s to two d i f f e r e n t lig h t i n t e n s i t i e s . It i s c l e a r t h a t p l a n t s t r e a t e d u n d e r low lig h t i n t e n s i t y sh ow a g r e a t e r r e s p o n s e t h a n p l a n t s t r e a t e d u n d e r a h ig h lig h t i n ­ te n sity . F ig u re X R e s p o n s e o f A . m a j u s to lig h t i n t e n s i t i e s . L e f t to r i g h t P lig h t. P , F . T op g ro w n a t low i irf 1 B o tto m g ro w n a t h ig h l ig h t. F ig u re X F i g u r e XI P h y s i o l o g i c a l r e s p o n s e of A . m a j u s to in d o le a c e tic acid . rig h t tre a te d . P l a n t s on le f t u n t r e a t e d , p l a n t s on G ro u p one P ^ , tw o P^, t h r e e F^. T o p 72 h o u r s a f t e r t r e a t m e n t in h ig h lig h t. B o tto m 72 h o u r s a f t e r t r e a t m e n t in low lig h t. -45- F i g u r e XI F i g u r e XII E f f e c t of lig h t i n t e n s i t y on th e p h y s io l o g i c a l r e s p o n s e of A . m a j u s to in d o le a c e t i c a c i d . Top p^, c en ter P ^, b o tto m F j . One t r e a t e d in low lig h t, tw o t r e a t e d in h ig h lig h t a n d t h r e e u n t r e a t e d . -46 F i g u r e XII -47- DISCUSSION D u r in g th e c o u r s e of th is e x p e r i m e n t , s o m e s ig n if ic a n t f a c t s in d ic a tin g a n i n t e r r e l a t i o n s h i p of in do le a c e t i c a c id , lig h t i n t e n s i t y a n d d e g r e e of h e t e r o s i s in A . m a ju s w e r e found. H e t e r o s i s i s d e f in ite ly e x h ib ite d in A . m a j u s . In E x ­ p e r i m e n t s I, II, a n d III a p o s it i v e h e t e r o s i s w a s o b ta in e d b o th a s to i n c r e a s e in d r y w e ig h t of the ly b rid a n d a s to i n ­ c r e a s e in h e ig h t of th e h y b r i d s . ( T a b le s 1 a n d 2). The s a m e d e g r e e of h e t e r o s i s w a s not e x h ib ite d a t a l l t i m e s . ( F i g u r e s 1, 2 a n d 3). I n .E x p e r i m e n t 1 th e d e g r e e of h e t e r o ­ s i s w a s v e r y s lig h t a s c o m p a r e d to E x p e r i m e n t s II a n d III. T h is v a r i a t i o n w a s c o n s i s t e n t a s to d r y w e ig h t i n c r e a s e a s w e ll a s to i n c r e a s e in h e ig h t. (T a b le 1 a n d 2). In E x p e r i m e n t I d u r in g th e w in te r w h en lig h t in te n s i ty w a s v e r y low th e d e g r e e of h e t e r o s i s w a s s lig h t. s i s i n c r e a s e d a s th e lig h t i n t e n s i t y i n c r e a s e d . H e te ro ­ ( F i g u r e IX). T h i s i n d i c a t e s t h a t s o l a r r a d i a t i o n i n flu e n c e s h e t e r o s i s in A. m a ju s. T h is is s u b s t a n t i a t e d by the l i n e a r i t y of the c u r v e in F i g u r e IX. T he e x p r e s s i o n of h e t e r o s i s in A . m a j u s c a n b e d i r e c t l y c o r r e l a t e d to s o l a r r a d i a t i o n . As th e lig h t i n t e n s i ty i n c r e a s e s th e d e g r e e of h e t e r o s i s i n ­ creases. -48- W hen A . m a ju s w a s r a i s e d u n d e r low lig h t i n t e n s i t i e s th e d i f f e r e n c e s b e t w e e n th e h y b r id an d the p a r e n t s w e r e s lig h t. W hen r a i s e d u n d e r a h ig h lig h t in te n s ity , th is d if f e r e n c e w as i n c r e a s e d a s show n in F i g u r e X. T h is a l s o i n d i c a t e s th a t th e in flu e n c e of lig h t on h e t e r o s i s is no t a p h o to p e r io d ic r e s p o n s e b u t a r e s p o n s e on th e d i r e c t i n c r e a s e in lig h t i n te n s ity . W hen p a r e n t s a n d th e h y b r id w e r e t r e a t e d w ith ind o le a c e t i c a c i d a d i f f e r e n t i a l in e p in a s tic r e s p o n s e w a s o b ta in e d . T h e i n b r e d s r e c o v e r e d f r o m th is e p in a s tic r e s p o n s e m o r e r a p i d l y th a n th e h y b r id . It w a s found th a t w h e n th e in b r e d s a n d h y b r i d s w e r e t r e a t e d w ith in d o le a c e t i c a c id u n d e r low lig h t i n t e n s i t i e s th a t th e r e s p o n s e was, g r e a t e r th a n w h en u n ­ d e r h ig h lig h t i n t e n s i t i e s . W hen p la n ts w e r e g ro w n u n d e r lo w lig h t th e i n b r e d s did no t r e c o v e r f r o m th e e p i n a s tic r e ­ s p o n s e of in d o le a c e t i c a c i d a s r a p i d l y a s w h en g ro w n u n d e r h ig h lig h t. T h is in d i c a t e s t h a t th e e p in a s tic r e s p o n s e of A . m a j u s to in d o le a c e t i c a c i d c a n be d i r e c t l y c o r r e l a t e d w ith s o l a r r a d i a t io n . B y u s in g a b io lo g ic a l t e s t , it w a s found th a t th e i n b r e d s h a v e a g r e a t e r a b i l it y to i n a c tiv a te o r in h ib it in d o le a c e t i c a c i d th a n th e h y b r i d s . T h is i n d i c a te s th a t th e i n b r e d s h av e a m e c h a n i s m t h a t in h ib its o r i n a c t i v a t e s in d o le a c e t i c a c id . S in c e th e i n b r e d s p o s s e s s a m e c h a n i s m t h a t in a c t i v a t e s in d o le a c e t i c a c i d a n d a l s o r e c o v e r s m o r e r a p i d l y w h e n t r e a t e d w ith in d o le a c e t i c a c i d a n d th e r e c o v e r y i s c o r r e l a t e d -4 9 - w ith s o l a r r a d i a t i o n , th a t th e i n a c t i v a t i o n o r in h ib itio n i s a l s o c o r r e l a t e d w ith lig h t. A l l e v id e n c e s e e m s to p o in t to th e f a c t t h a t th e e x p r e s s i o n of h e t e r o s i s in A . m a j u s is d i r e c t l y c o r r e l a t e d w ith s o l a r r a d i a ­ tio n . W hen A . m a j u s w a s r a i s e d u n d e r low lig h t i n t e n s i t i e s , th e d if f e r e n c e b e t w e e n th e h y b r id a n d p a r e n t w a s v e r y s lig h t. W h en t h e y w e r e r a i s e d u n d e r h ig h lig h t i n te n s ity , t h is d i f f e r ­ e n c e w a s v e r y s ig n i f ic a n t a s sho w n in F i g u r e X. P h o to s y n th e tic a r e a of a p l a n t m a y be a n i m p o r t a n t f a c t o r in d e t e r m i n i n g th e a m o u n t of r a d i a n t e n e r g y t h a t c a n be u s e d in p h o to sy n th esis. T h e g r e a t e r a b i l i t y of h y b r id s to r e t a i n a n d u t i l i z e g r o w th s u b s t a n c e u n d e r h ig h lig h t c o n d itio n s p e r m i t s g r e a t e r e x p a n s io n of p h o to s y n th e tic a r e a . The clo se re la tio n h e r e d e m o n s t r a t e d b e tw e e n g r o w th s u b s t a n c e r e s p o n s e , s o l a r r a d i a t i o n , a n d h e t e r o s i s give a b u n d a n t e v id e n c e f o r th e p r o p o ­ s i t i o n t h a t h e t e r o s i s in th is h y b r id m a y b e p r i m a r i l y due to t h i s m e c h a n is m .. A s C r a b b (10) h a s show n, th e to ta l s o l a r r a d i a t i o n v a r i e s f r o m l o c a l i t y to l o c a l i t y a n d one w o u ld not e x p e c t th e s a m e r e ­ s p o n s e f r o m th e s a m e c r o p r a i s e d in d if f e r e n t l o c a l i t i e s . It is k now n t h a t th e r e s p o n s e of v a r i o u s h y b r id s n a p d r a g o n s d i f f e r s w ith d i f f e r e n t l o c a l i t i e s . T h e b io lo g ic a l t e s t sh o w s th a t a n i n h ib ito r o r a n i n a c t i v a ­ t o r w a s p r e s e n t in th e i n b r e d s a n d th a t t h is i n h ib ito r in i n a c ­ t i v a t o r i s n o t a s e f f e c t i v e in th e h y b r i d s . T h is c o u ld e x p la in -5 0 - w hy th e h y b r i d s a r e m o r e v ig o r o u s th a n th e i n b r e d s u n d e r h ig h lig h t i n t e n s i t y . In th e i n b r e d s u n d e r h ig h lig h t i n t e n ­ s i t i e s , g r o w th s u b s t a n c e s a r e in a c t i v a t e d a n d in th e h y b r id s th e g r o w th s u b s t a n c e s a r e n o t i n a c t i v a t e d . A s a r e s u l t of th i s , th e h y b rid s a r e a b le to g r o w m o r e r a p i d l y th a n th e i n ­ breds. T h i s a l s o e x p la in s w hy u n d e r d a r k c lo u d y w e a t h e r c h a r a c t e r i s t i c of f a l l a n d w i n t e r , t h e r e i s l i tt l e d if f e r e n c e b e t w e e n t h e s e i n b r e d s a n d th e h y b r i d s . T h e g r o w th s u b s t a n c e s a r e n o t i n a c t i v a t e d u n d e r low lig h t a n d th e i n b r e d s a r e p e r m i t t e d to e x p a n d m o r e , p r e ­ s e n t i n g m o r e l e a f a r e a f o r p h o to s y n th e tic a c tiv ity ; th u s r e s u l t i n g in m o r e e f fic ie n t g ro w th . T h is d o e s n o t i n d i c a t e th a t t h is is a lw a y s th e c a s e an d w ith o u t a do u bt s o m e i n b r e d s of A . m a ju s do n ot c o n ta in th is i n h i b it o r o r i n a c t i v a t o r . T h e y w ou ld p r o d u c e a h y b r id th a t w o u ld b e e x c e l l e n t u n d e r low lig h t c o n d itio n s . T h is i s the r e a s o n w hy h y b r i d s a r e l i m i t e d to a r e a s w h e r e th e y a r e a d ap ted . T h is c o u ld e x p la in why t h e r e a r e h y b r id s t h a t r e ­ s p o n d w e l l in th e s p r i n g . I n d ic a tio n s of t h is w o r k w a r r a n t f u r t h e r i n v e s t i g a t i o n s a lo n g b i o - c h e m i c a l l i n e s a i m e d a t i s o l a t i n g th e in h i b i t o r o r i n a c t i v a t o r . T h e find ing of t h i s in h i b i t o r o r i n a c t i v a t o r w o u ld h e lp give th e e x a c t m e c h a n ­ i s m a n d th e p h y s io l o g i c a l p r o c e s s th a t i s in v o lv e d . These t r e a t m e n t s s h o u ld b e t r i e d w ith o th e r c r o p s d is p la y in g h e t e r o s i s s u c h a s c o r n , t o m a to e s , e t c . to s e e if th e y give -5 1 - th e s a m e r e s p o n s e . G e n e tic a n a l y s i s of q u a n tita tiv e i n h e r i t a n c e h a s b e e n foun d d iff ic u lt in the p a s t . C o n s i d e r a t i o n of th e e ffe c t of lig h t on the e x p r e s s i o n of h e t e r o s i s w ill r e d u c e u n w an ted v a r i a t i o n b e tw e e n e x p e r i m e n t s . S in c e e a c h a d d itio n a l g e n e tic f a c t o r i n c r e a s e s th e m i n im u m p o p u la tio n f o r c o m ­ p l e t e F ^ s e g r e g a t i o n b y f o u r t i m e s th e i s o l a t i o n of th is m e c h a n i s m f r o m o t h e r f a c t o r s f o r q u a n tita tiv e i n h e r it a n c e a f f o r d s c o n s i d e r a b l e s im p l i f i c a t i o n of th e w hole t a s k . -52- CONCLUSION 1. It w a s fo u n d t h a t A n t i r r h i n u m m a ju s L . d e f in ite ly e x h ib its h e t e r o s i s . 2. T h e d e g r e e of h e t e r o s i s e x h ib ite d i s d i r e c t l y c o r r e ­ l a t e d w ith s o l a r r a d i a t i on. 3. T r e a t m e n t w i t h in d o le a c e t i c a c i d i n d i c a t e d t h a t h y b r i d s sh o w g r e a t e r e p in a s ti c r e s p o n s e th a n e i t h e r p a r ­ e n t. 4. A b io lo g ic a l t e s t s h o w e d th a t th e i n b r e d s h a v e a m o r e e f fe c tiv e m e c h a n i s m of in a c ti v a t i n g o r in h ib itin g the e f f e c t s of in d o le a c e t i c a c id . 5. W hen th e i n b r e d s a n d h y b r id s a r e g ro w n u n d e r low lig h t i n t e n s i t i e s , th e d e g r e e of h e t e r o s i s is v e r y s lig h t. 6. T h e e p i n a s t i c r e s p o n s e of A . m a j u s to in d o le a c e ­ tic a c i d i s d i r e c t l y c o r r e l a t e d w ith lig h t. T he i n b r e d s show a h i g h e r d e g r e e of e p i n a s ty u n d e r low lig h t th a n u n d e r h ig h lig h t. W hen th e p l a n t s a r e g ro w n u n d e r h ig h light, th e y r e c o v e r f r o m th e e p in a s ty c a u s e d by in d o le a c e t i c a c i d m o r e ra p id ly . response. T h e h y b r id s do no t r e c o v e r a s r a p i d l y f r o m th is -53- BIB L IO G R A PH Y 1. A l a m e r c e r y , J . 1952. T h e i n t e r a c t i v e e f fe c ts of c o u m a r i n d ith io o x a m id e a s c o r b i c a c i d a n d a u x in s upon th e e a r l y d e v e lo p m e n t of r o o t s , (u n p u b lis h e d t h e s i s ) . 2 . A s h b y , E . 1930. S tu d ie s in th e i n h e r i t a n c e of p h y s io l o g i ­ c a l c h a r a c t e r s . . I. A p h y s io l o g i c a l in v e s t i g a t i o n of th e n a t u r e of h y b r id v ig o u r in m a i z e . A n n. B o t. 4 4 :4 5 7 -4 6 7 . 3. _________ . 1932. S tu d ie s in th e i n h e r i t a n c e of p h y s io lo g ic a l c h a r a c t e r s . II. F u r t h e r e x p e r i m e n t s upon th e b a s i s of h y b r id v ig o u r a n d u po n th e i n h e r i t a n c e of e f fic ie n c y in d e x a n d r e s p i r a t i o n r a t e in m a i z e . A n n. B o t. 46:1007-1032. 4. . 1936. H y b r id v ig o u r in m a i z e . 70:179-181. 5. . 1937. S tu d ie s in th e i n h e r i t a n c e of p h y s io lo g ic a l c h a r a c t e r s . III. H y b r id v ig o u r in th e to m a to . I. M a n i ­ f e s t a t i o n s of h y b r i d v ig o u r f r o m g e r m i n a t i o n to th e o n s e t of f lo w e r in g . A nn . B o t. 1 :1 1 -4 1 . 6 . B au er, E . 11th ed. A m . N a t. 1930. E in f u r u n g in die v e r b u g e l c h r e . B erlin . 7. B e a d le , G. W. a n d E . L . T a tu m . 1941. G e n e tic c o n t r o l of b i o c h e m i c a l r e a c t i o n s in N e u r o s p o r a . P r o c . N a t. A c a d . S c i. 2 7 :4 9 9 -5 0 6 . 8 . B o y s e n J e n s e n , P . 1928. Die p h o t o t r o p is c h e in d u k tio n in d e t S p itz e d e r A v e n a k o le o p tile . P l a n t a 5 :4 6 4 -4 7 7 . 9. B u r k h o l d e r , P . R . a n d E . S. J o h n s t o n . I n a c tiv a tio n of p la n t g r o w th s u b s t a n c e s b y lig h t. S m i t h s o n i a n M is c . C o ll. V ol. 95, N o. 20. 1937. 10. C r a b b , G . A . , J r . 1950. S o la r r a d i a t i o n i n v e s t ig a t io n s in m i c h ig a n . M ic h . A g r . E x p . S ta . T e c h . B u i. 222. M ic h ig a n S ta te C o lle g e , E a s t L a n s in g , M ic h ig a n . . 1952. T he n o r m a l p a t t e r n of s o l a r r a d i a t i o n a t E a s t L a n s i n g , M ic h ig a n . M ic h ig a n A c a d e m y of S c ie n c e , A r t s a n d L e t t e r s , Vol. XXXVI. (in p r e s s ) 12 E a s t , E . M . 1908. I n b r e e d in g in c o r n . E x p . S ta . f o r 1907. 4 1 9 -4 2 8 . R e p t. C on n. A g r . -54- 13. _____ . 1909. T h e d i s t in c t i o n b e tw e e n d e v e lo p m e n t a n d h e r e d i t y in in breedin g.- A m . N a t. 4 3 :1 7 3 -1 8 1 . 14. . 1935. G e n e tic r e a c t i o n s in N ic o tia n a . I. C o m p a t i b il i t y . H. P h e n o ty p ic r e a c t i o n p a t t e r n s . III. D o m in a n c e . G e n e t ic s 2 0 :4 0 3 -4 5 1 . 15. _________ . 1936. H e te ro sis. G e n e tic s 2 1 :3 7 5 -3 9 7 . 1 6 . ______ a nd H. K. H a y e s . 1912. e v o lu tio n a n d in p la n t b r e e d i n g . B u r . P I . I n d . , B u i. 2 4 3 :1 -5 8 . H e t e r o z y g o s i s in U . S. D ep t. A g r . , 17. G a ls to n , A . W. a n d R o sam o n d S. B a k e r . 1949. S tu d ie s on th e p h y s io lo g y of lig h t a c t i o n . II. T h e p h o to d y n a m ic a c t i o n of r ib o f l a v i n . A m e r . J o u r n . B o t. V ol. 36. N o . 36. 7 7 3 -7 8 0 . 18. G a r t n e r , C . F . 1849. 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G e n e tic s 6 :4 3 3 -4 4 4 . 25# . 1939. C o n tin u e d i n b r e e d i n g in m a i z e . U e n e t i c s 2 4 :4 6 2 -4 7 3 . 26. K e e b le , F . , a n d P e l l e w . 1910. T h e m o d e of i n h e r i t a n c e of s t a t u r e a n d of t i m e of flo w e rin g in P e a s . (P i s u m s a tiv u m ) J o u r . G e n e tic s 1 :4 7 -5 6 . -55- 2 7 . K o l r e u t e r , J . G* 1766. D r i t t e F o r t e s e t z u n g d e r v o r a u f i g e n N a c h r i c h t von e in ig e n d a s G e s c h l e c h t d e r P f l a n z e n b e t r e f f e n d e n V e r s u c h e n u n d B e o b a c h tu n g e n . G l e d i t s c h e n H an d lu n g . 1766. ( R e p r i n te d 1893 in O s t w a l d 's K l a s s i k e r d e r E x a k te n W is s e n s c h a f te n , N o. 4 1 .) 2 8 . K r o n e P . K. a n d B u l m e r G. 1951. L ig h t i n t e n s i t y u n d e r V a rio u s sh a d e s. M ic h ig a n F l o r i s t . N o. 243. J u l y 1951. 29. L i n d s t r o m , E . W. 1925. H e r i t a b l e c h a r a c t e r s in m a i z e . XVI (XXI) - - A n ew d o m in a n t h e r e d i t a r y c h a r a c t e r - - te o p o d . J o u r . H e r e d . 1 6 :13 5-14 0 . 30. __________________ . 1935. G e n e tic e x p e r i m e n t s on h y b r i d v i g o r i n m a i z e . A m . N a t. 6 9 :3 1 1 -3 2 2 . 31. __________________ . 1939. A n a l y s is of m o d e r n m a i z e b r e e d i n g p r i n c i p l e s a n d m e th o d s . P r o c . 7th In t. G e n e t. Cong: 19 1-1 96 . 32. M a lin o w s k i, E . 1928. A p e c u l i a r c a s e of h e t e r o s i s in P h a s c o l u s v u l g a r i s . L . Z e i t s . In. A b s t. V e r . , S u pp l. 2 :1 0 9 0 -1 0 9 3 . 33. . 1935. S tu d ie s on h y b r id v ig o u r in P h a s e o l u s v u l g a r i s ( L . ) S av i. P t . I. V ig o ro u s s i z e s a n d p h o to p e r io d ic r e s p o n s e of the F j p l a n t s . Z e i t s . Ind. A b s t . V e r . 7 0 :9 6 -1 2 4 . 34. M o rg a n , T . H. e t a l . 1915. h e r e d i t y . XIII + 262 pp. M e c h a n i s m of M e n d e lia n 35. P o s t , K. 1950. F l o r i s t C r o p p r o d u c tio n a n d m a r k e t i n g . O r a n g e J u d d P u b l i s h i n g C o . N. Y . , N . Y . p p . 3 2 5 -3 3 7 . 3 6 . R o b b in s , W m . J . 1940. G ro w th s u b s t a n c e s in a h y b r id c o r n a n d i t s p a r e n t s . B u i. T o r r e y B o t. Club 6 7 :5 6 5 574. 37^ . 1941. G r o w th of e x c i s e d r o o t s a n d — h e te ro S iS lfT tb m a to . A m . J o u r . B o t. 2 8 :2 1 6 -2 2 5 . 38. Shull, G. H. 1911. 4 5 :2 3 4 -2 5 2 . 39# T he g e n o ty p e s of m a i z e . A m . N a t. . 1914. D u p lic a te d g e n e s f o r c a p s u le f o r m in B u r s a b u r s a P a s t o r i s . Z e i t s . Ind. A b s t. V e r . 12:9T-l¥9" -56- 4 0 . S in g le to n , W. R . 1941. H y b r id v ig o r a n d it s u t i l iz a t i o n in s w e e t c o r n b r e e d i n g . A m . N a t. 7 5 :4 8 -6 0 . 41. Skoog, F o l k e . 1947. G r o w th s u b s t a n c e s in h i g h e r p l a n t s . A n n u a l R e v . B io . C h e m . V. XVI. 42. ________ . 1951. P l a n t g ro w th s u b s t a n c e s . s it y of W is c o n s in P r e s s , p p . 2 6 3 -2 8 5 . 4 3. 44. U n iv e r- T a tu m E . L . 1939. D e v e lo p m e n t of e y e - c o l o r s in d r o s p h i l a . B a c t e r i a l s y n t h e s i s of v. + h a r m o n e . N a t. A c a d . S oc. 2 5 :4 8 6 -4 9 0 . P roc. , a n d G. W. B e a d le . 1942. T he r e l a t i o n of g e n e tic s to g r o w th - - f a c t o r s a n d h a r m o n e s . G ro w th 6 :2 7 -3 5 . 45. U l r ic h , A . 1940. M e a s u r e m e n t of th e r e s p i r a t o r y q u o tie n t of p l a n t t i s s u e s in a c o n s ta n t g a s e o u s e n v ir o n m e n t. P l a n t P h y s i o lo g y 1 5 :5 2 7 -5 3 6 . 4 6 . V an O v e r b e e k . 1938. " L a z i n e s s " in m a i z e due to a b n o r m a l d i s t r i b u t i o n of g r o w th h a r m o n e . J . H e r e d . 2 9 :3 3 9 -3 4 1 . 47. 48. W a r b u rg , O . 1914. Z e it, p h y s io lo g y C h e m i s t r y 92:231. . 1926. U b e r d eu s to f f w e c h s e l d e r T u m o r e n S p r in g e r , B e r l i n ( E n g lis h t r a n s l a t i o n by F . D ic k e n s , 1930, C o n s ta b le L o n d o n . 4 9 . W ent, F . W. a n d K. V. T h im a n n . M a c M illa n C o . , N ew Y o rk . 1937. P h y to h o rm o n es. 50. W haley , W. G. 1939. A d e v e lo p m e n t a n a l y s is of h e t e r o s i s in L y c o p e r s i c o n . A m . J o u r . B o t. 2 6 :6 0 9 -6 1 6 , 6 8 2 -6 9 0 . 51. . 1944. H e te ro sis. B o t. R e v . 10:461-498. 52. a n d A l i c e L o n g . 1944. T h e b e h a v io r of e x c i s e d r o o t s of h e t e r o t i c h y b r id s a n d t h e i r i n b r e d p a r e n t s in c u l t u r e . B u i. T o r r e y B ot. Club 7 1 :2 6 7 -2 7 5 . 53# e t a l. T he g ro w th of h y b r id a n d i n b r e d m a i z e e m b r y o s in lig h t a n d in d a r k n e s s . (U n p u b lish ed ). 54. W ittw e r, S. H. 1949. E f f e c t of f r u i t s e ttin g t r e a t m e n t v a r i e t y a n d s o l a r r a d i a t i o n on y ie ld a n d f r u i t s iz e of g r e e n h o u s e t o m a t o e s . P r o c . A . S . H . S . V ol. 5 3 :3 4 9 -3 5 4 . -57- 55. W ittw e r, S. H. E f f e c t of in d o le a c e t i c a c i d a n d lig h t i n t e n s i t y on f r u i t s e t of t o m a t o e s . ( P e r s o n a l c o m ­ m u n ic a tio n ) . A P P E N D IX A P P E N D IX I P r e lim in a r y E x p e rim en tatio n To d e t e r m i n e th e e ffe c t of g r o w th s u b s t a n c e s on two i n ­ b r e d s a n d t h e i r h y b r i d s , s e e d lin g s w e r e g ro w n in p e t r i d i s h e s f i l l e d w ith a q u a r t z s a n d a n d h av in g t h r e e r e p l i c a t i o n s p e r tre a tm e n t. T h e q u a r t z s a n d w a s t r e a t e d w ith the f o l ­ lo w ing s u b s t a n c e s a t th e r a t e s of 10, 1, 1/ 10, a n d 1 /1 0 0 ppm . 1. n i c o t i n i c a c i d 2 . fo lic a c i d 3. r ib o f l a v i n 4 . c h o lin e 5. c a l c i u m p e n ta th e n a te 6 . p y r id o x in e h y d r o c h l o r i d e 7. th i a m in e h y d r o c h l o r i d e i 8 . a s c o rb ic acid 9 . in d o le a c e t ic a c i d 10. 2 - 3 - 5 t r i - i o t a b e n z o ic a c i d 11. n a p th a le n e a c e t i c a c id 12. a c o m b in a tio n of one th ro u g h n in e 13. a c o m b in a tio n of n in e th ro u g h e le v e n . T h is t r i a l w a s r e p e a t e d t h r e e t i m e s . G ro w in g p l a n t s w e r e s p r a y e d w ith the ab o v e c o m p o u n d s. R e s p o n s e to t h e s e c o m p o u n d s w e r e o b s e r v e d to d e t e r m i n e th e c o m p o u n d s e ffe c tin g h e t e r o s i s . S eeds w e re also soaked f o r a p e r i o d of tw e n t y - f o u r h o u r s p r i o r to sow ing a n d g e r m i ­ n a t e d w ith a n d w ith o u t th e ab o v e m a t e r i a l s . No c o n s i s t e n t r e s u l t s w e r e o b ta in e d on g e r m in a ti o n of t h e s e s u b s t a n c e s o r b y t r e a t i n g th e s e e d s . O n ly one c o m p o u n d s h o w ed a d i f f e r ­ e n t i a l c o r r e l a t e d w ith h e t e r o s i s a n d t h i s s u b s ta n c e w a s ind o le a c e tic a cid . F u r t h e r d e t e r m in a t i o n s w e r e m a d e on p la n t s g r o w n in p o ts w ith th e c o n c e n t r a t i o n s b e in g v a r i e d f r o m 5 p p m . up to 1000 p p m . A f te r th e f a v o r a b l e c o n c e n t r a t i o n s w e r e d e t e r m i n e d p la n t s g ro w in g in a g r e e n h o u s e b e n c h w e r e r a n d o m i z e d in g r o u p s of f o r t y p l a n t s having t h r e e r e p l ic a t i o n s of each tre a tm e n t. S in c e th is t r e a t m e n t g av e c o n s is t e n t r e ­ s u lt s a n d t h e r e w e r e d i f f e r e n c e s in r e s p o n s e b e tw e e n in b r e d s a n d h y b r i d s , a g r e e n h o u s e b e n c h of P p P 2 , F^ a n d F 2 w a s t r e a t e d a t 100 p p m . of in d o le a c e t i c a c id , V ig o r a n d r e s p o n s e to in d o le a c e t i c a c i d w e r e r e c o r d e d . II T i s s u e A n a l y s is To d e t e r m i n e th e c h e m i c a l a n a l y s i s of t h e s e p la n ts a n d to f in d out if t h e r e w a s a n y d if f e r e n c e b e tw e e n i n b r e d s a n d h y b r id s a s w e l l a s b e tw e e n t r e a t e d a n d u n t r e a t e d p la n ts , d e t e r m i n a ti o n s w e r e m a d e in d u p lic a te on a s h , c r u d e f ib e r , ether e x t r a c t , p r o ­ te in , n i tr o g e n , c a l c i u m , p h o s p h o r u s , a n d p o t a s s i u m . P lan ts u s e d f o r t h e s e d e t e r m i n a t i o n s w e r e r a i s e d in g r o u p s of e ig h ty p l a n t s a n d r a n d o m i z e d w ith t h r e e r e p l i c a t i o n s . C h e m i c a l A n a l y s is of P^, P ^ , a n d S a m p le A s h 1 N o. C rude E th e r F ib e r2 ex­ tra c t P ro- 3 te rn N -free ex- 7 tra c t Ca P K P2 check 1418 1 0 .2 7 2 . 59 3 4 .8 1 38. 15 P2 IAA* 1 4 .2 1 10. 15 2 .6 5 35. 50 3 7 .4 9 2. 38 P1 check 15. 78 8 .4 0 2 . 19 37. 94 3 5 .6 9 2 . 12 . 704 3. 98 1 5 .9 6 8 . 58 2 . 86 37. 75 3 4 .8 5 2 . 11 .6 8 4 4 . 2 3 1 4 .4 5 10. 45 2 .8 3 36. 06 36. 21 2 . 09 . 578 3. 75 15. 03 1 0 .3 7 3 .2 5 35. 94 3 5 .4 1 2 .0 4 . 580 3 .8 6 pi IAA - F1 check n IAA 2 .4 2 . 574 3 .4 4 . 566 3. 72 * In d o le a c e t i c a c i d ^ A v erag es of r e s u l t s f r o m d u p lic a te d e t e r m i n a t i o n s e x p r e s s e d on th e o v e n - d r y b a s i s . 2 T h e s u m of th e v a l u e s fo r c r u d e f ib e r a n d n i t r o g e n - f r e e e x t r a c t g iv e s a n e s t i m a t i o n of th e t o t a l c a r b o h y d r a t e of th e t i s s u e . ^ECje Ida hi n i t r o g e n x 6 . 2 5 . I ll R iv o f la v in D ata S in c e G a ls to n (17) h a s show n th a t r ib o f la v in i n a c t i v a t e d in d o le a c e t i c a c i d in th e p r e s e n c e of lig h t a n d th e r e s p o n s e of th e i n b r e d s in d i c a t e d t h a t in d o le a c e t i c a c i d w a s i n a c t i v a t e d iv in th e p r e s e n c e of lig h t, th e t i s s u e w a s a n a l y z e d b io lo g ic a lly f o r r ib o f la v in . R e s u l t s of t h e s e t e s t s a r e g iv e n b elow : R ib o f la v in A n a l y s i s of P p P ^ , an d F^ T reated * U n tr e a te d * P1 13. 75 15. 26 P2 13. 5 1 3.46 P3 1 3 .2 9 13. 32 ^ v a l u e s a r e in m i l l i g r a m s p e r pou nd . IV C y to lo g ic a l D a ta To o b ta in c y to lo g ic a l d ata, m e o s i s a n d m i t o s i s w e r e s tu d i e d on P p P 2 a n d F 1 p l a n t s t r e a t e d a n d u n t r e a t e d w ith in d o le a c e t i c a c id . n o rm a l. M eo sis and m ito sis w e re ap p aren tly A ll a r e d ip lo id w ith e ig h t p a i r s of c h r o m o s o m e s . V R e s p i r a t i o n D ata R e s p i r a t i o n s t u d i e s w e r e m a d e on g e r m i n a t e d s e e d lin g s b y u s in g th e W a r b u r g m e th o d (47, 48) a n d g ro w in g p la n t s w e r e m e a s u r e d f o r r e s p i r a t i o n b y th e U l r i c h (45) m e th o d V a n d no d i f f e r e n c e s w e r e o b ta in e d b e tw e e n t r e a t e d o r u n t r e a t e d o r b e tw e e n i n b r e d s o r h y b r i d s . VI F r e s h a n d D r y W e ig h ts of T r e a t e d a n d U n t r e a t e d P l a n t s To d e t e r m i n e d i f f e r e n c e s in f r e s h a n d d r y w e ig h ts of t r e a t e d a n d u n t r e a t e d p la n t s , lo ts of 350 p la n t s e a c h of P p P 2, a n d F 1 w e r e t r e a t e d , a n d a v e r a g e w e ig h ts w e r e o b ta in e d . R esu lts a r e g iv e n in th e t a b l e b elo w : D r y W eigh t H a r v e s t e d M a r c h 19, 1952 Exp I A v e r a g e of 350 p l a n ts A verage fre s h w t. p e r p la n t A verage dry w t. p e r p la n t P £ check P 2 t r e a t e d IAA* 3 .6 3. 48 . 371 . 357 P^ c h e c k t r e a t e d IAA* 2. 15 2. 34 . 195 .2 1 6 F j check F]^ t r e a t e d IAA* 3. 93 4 .4 7 .4 0 1 .3 9 4 * in d o le a c e t i c a c id D r y W eig h t H a r v e s t e d A p r i l 14, 1952 E x p II A v e r a g e 350 p la n ts A verage fre s h w t. p e r p la n t check t r e a t e d IAA* A v erag e dry w t. p e r p la n t 2 .4 8 2. 38 .2 06 . 225 P j check p ^ t r e a t e d IIA* 2 .8 5 3. 07 .2 3 1 . 252 F„ c h e c k £1 F^ t r e a t e d IAA* 6 .4 2 5 .6 4 .5 7 .5 3 9 D r y W eig ht H a r v e s t e d M ay 16, 1952 E x p III A v e r a g e 350 p la n ts A verage fre s h w t. p e r p la n t A v erag e dry w t. p e r p la n t P ^ check P ^ t r e a t e d IAA* 2 .4 4 2. 52 . 16 .2 P^ c h e c k p t r e a t e d IAA* *1 1 .6 1.88 . 12 . 16 6 .8 .6 5. 32 .5 4 check F-| t r e a t e d IAA* * in d o le a c e t i c a c id No s ig n i f ic a n t d i f f e r e n c e s w e r e o b ta in e d in th e m e a s u r e ­ m e n t s of t h e s e f r e s h a n d d r y w e ig h ts b e tw e e n t r e a t e d a n d u n ­ tr e a te d p la n ts. VII S o l a r R a d ia tio n R aw chta f o r th e s o l a r r a d i a t io n f r o m D e c e m b e r 1951 t h r o u g h M ay 1952 w h ic h w a s u s e d in m a k in g G r a p h IV is p r e ­ s e n t e d b elo w : S o la r R a d i a t i o n g r a m c a l o r i e s p e r sq . c m . D e c e m b e r 1, 1951 - M ay 15, 1952 W eek ly Ave. T o ta l 1-5 A ve. Decem ber 1951 J an u ary F e b ru a ry M arch A p ril M ay 6 1 1 .3 0 4 8 7 .5 3 2 8 .4 0 9 0 5 .6 0 7 3 6 .7 0 2 7 7 0 .0 1 0 2 .2 6 97. 5 65. 68 1 8 1 .1 2 1 4 7 .3 4 T o tal 6 -1 0 Ave. 4 13 . 5 3 4 4 .6 6 2 3 .6 0 1 3 4 9 .0 1 2 4 .7 2 269. 8 T o tal 11-15 A ve. 424. 5 8 4 .9 79. 14 T o tal 16-20 A ve. T o tal 2 1 -2 5 A ve. 5 2 9 .6 0 4 0 7 .7 0 T o ta l 26-30 A ve. 82. 7 1 0 5 .9 2 4 0 1 .8 0 6 8 . 92 3 9 5 .7 0 1 0 7 0 .6 0 2 1 4 .1 2 1024.0 81. 54 2 0 4 .8 5 0 7 .4 0 1222.70 1 748.90 1904.1 3 4 9 .7 8 3 8 0 .8 1 5 3 7 .8 0 1 1 4 2 .3 0 1 9 1 6 .4 3 0 7 .5 6 2 2 8 .4 6 1 015.90 2 5 4 6 .1 0 2 0 3 .1 8 5 0 9 .2 5 1 41 2.40 1 8 2 9 .4 0 80. 36 1 01 .4 8 2 4 4 .5 4 2 8 2 .4 8 3 6 5 .8 8 5 3 9 .4 0 732. 5 7 6 3 .3 0 1 808.10 2 8 8 .0 1 8 9 .9 1 2 2 .0 8 1 9 0 .8 3 3 0 1 .3 5 5 7 .6 0 M o n th ly 2 9 2 0 .4 T o tal M o n th ly 9 4 .2 A verage 5 5 4 .0 2 8 7 5 .4 5 0 3 2 .6 8 0 2 8 .8 92. 8 173. 5 259. 0 1 08 83 .5 3 6 2 .8 3 8 3 .3 v iii VIII D a ta f o r C o r r e l a t i o n of V ig o r an d R e s p o n s e to G ro w th S u b stan ce s. T h e fo llo w in g t a b l e s a r e th e h e ig h t a n d r e s p o n s e to in d o le a c e t i c a c i d d a ta t h a t w a s u s e d in o b ta in in g the c o r r e l a t i o n . E x p e rim e n t I C o r r e l a t i o n of h e ig h t v e r s u s r e s p o n s e of s e g r e g a ti n g p o p u la tio n (F ^) to in d o le a c e t i c a c id . R esponse to indole acetic acid V ig o r 4 5 6 7 8 9 10 11 0 2 3 4 6 6 4 6 2 1 1 9 8 7 6 13 14 2 3 2 7 5 13 9 5 3 1 1 4 8 3 2 3 1 1 4 5 12 1 3 2 ix E x p e r i m e n t II C o r r e l a t i o n of h e ig h t v e r s u s r e s p o n s e of s e g r e g a t i n g p o p u la tio n (F ^) to in d o le a c e t i c a c id . Vigo r 3 4 5 6 7 8 9 10 11 12 1 1 7 10 11 5 10 6 2 3 10 17 26 32 28 2 5 11 23 50 57 1 2 5 14 27 46 1 1 to indole acetic acid 0 1 2 3 4 Response 2 5 1 5 13 14 18 6 1 50 37 13 3 49 43 35 9 3 7 15 16 14 10 3 1 1 1 1 2 x C o r r e l a t i o n of h e ig h t v e r s u s r e s p o n s e of s e g r e g a ti n g p o p u la tio n (F ^ ) to in d o le a c e t i c a c id . Response to indole acetic acid V ig o r 3 4 5 6 7 8 0 2 4 7 7 7 3 1 8 27 40 47 42 2 4 25 43 74 9 3 3 4 5 1 9 10 11 14 7 2 1 58 34 17 8 35 89 106 75 46 17 6 10 34 48 52 42 25 5 2 2 9 2 4 10 5 12 13 3 1 1