IIIHIIHHI lllHl i i l l WW! I ( l ll! _| I U) Sawy‘ivi QE‘e’ELQPMEfiT Efi CZLZW’ 33:3 é%4$é.L3EP€€ED EY C‘LEEETMN {ERQWTE REflfiLfiTQRS ”f'hmés {@5- ma flag?“ 9% M. 5-. PfifififiifiAH STATE COLLEGE ' 3'? . ”E .3, g " mrr n. z“ ' ' méfiwaisyn mGrg-mdu quiter I948 f. _ This is to certify that the t‘ r ' #7 them entitled . Sedetalk Develommt. 1n Celery ' I . f, as Influenced by Certain Growth Regulators } ‘ presented by , ~~ ' ‘ f L Llewellyn LeGrande Conlter : . has been accepted towards fulfillment ? ‘. I of the requirement: for 19. ._ . H. 30 degree in Horticultura L I ‘ ‘ f: E' mm L . . l. ~ [ - r V.._.3 ‘ I i i l i. Q SEEDSTAIK DEVELOPMEQT IN CEERY AS INFLUE‘ICED BY CERTAIN GROWTH REGULATORS By LLEWELLm LEGRANDE ggmgm A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture March 1948 __-_,...J THESIS ‘HQF—q n,—-_“'—_—. ~Wflk¥ ACKNOWLEDGMENTS The writer wishes to acknowledge his indebtedness to Dr. S. H. Wittwer for his wholehearted assistance throughout the course of the experiment and in the prep- aration of the manuscript. Appreciation is also extended to Dr. R. L. Carolus for his encouragement and valuable suggestions. 198850 SEEDSTAIK DIVEOPMMT IN GELEIH AS INFLUENCED BY CERTAIN GROWTH REGULATORS EIBQIUCTION Premature seeding, frequently referred to as “bolt- ing", is one of the most serious problems in production of the early crcp of celery. The plants, normally biennial, deve10p as annuals and produce seedstalks the first year. Deve10pment of a full and tender heart is replaced by the growth of a massive seedstalk. When this. happens a crop having a potential value of at least $400 per acre, becomes worthless. Thompson (17) has investigated this premature seeding and has dmnonstrated that its inception is primar- ily a result of the exposure of early spring plantings to low temperatures. Initiation of primordia and subsequent develOpment of seedstalks occurs when plants are exposed to a tanperature of 40-50 degrees for a period of two weeks or more. These conditions are frequently associated“ with the climatic areas where the highest quality celery is grown and for this reason the problem applies particularly to Michigan, New York, and California. In general, the varieties which normally produce the earlier, higher quality celery are the ones most likely to deve10p seedstalks prematurely. Control of this untimely flowering would eliminate the risk of loss and permit the production of an early high quality crap. The production of superior varieties which is now limited to the more tem- -2- perate areas and to late plantings in northern climates, might be expanded to any celery producing locality. The crap could be started in the field earlier and the grower would be able to take advantage of the higher prices of- fered by an early market for a high quality celery. A number of methods have been tried to prevent seed- ing with varying degrees of success. Growers have adopted the practice of hardening their plants by withholding water rather than by exposing them to low temperatures. This procedure has somevdiat reduced the amount of seedbed induc- ticn of flowering but does not influence the amount of floral initiation, which mu afterward occur in the field. Portable covers have been devised for protection of plants in the field. These covers are suitable for protection against freezing tennperatures of short duration but their use is expensive and they do not protect plants from con- tinued low tanperatures which promote premature seeding. Varieties, having non-bolting tendencies, have been intro- duced. They are very resistant to bolting but unfortunate- ly do not provide the grower with a high quality celery for the early market. _The above procedures, including protec- tive plant covers, late plantings and varieties resistant to bolting, have not yet provided a practical control of premature seeding. 0n the assumption that some chemicals of the plant growth regulator type might have the faculty to affect the initiation of flowering and subsequent seedstalk develcpment in celery, a number of experiments were designed to test the hypothesis. EWOF Recent investigations concerned with the control of reproductive and vegetative, development in plants have re- vealed mam' intricate relationships which the carbohydrate- nitrogen ratio hypothesis (14) does not adequately explain. The role of photoperiodism established by Garner andde (9) and of vernalization, as reviewed by mte (24), inaugu- rated a new line of research to determine the mechanisms controlling plant develOpment. CaJlachJan (l) conducted a number of experiments with two species, Chrysanthemum undicum and Perilla nankinensis, which are particularly sensitive to photOperiod. He concluded that flowering in these two species is induced by a material, ('florigen') which is synthesized in the leaves and translccated to the buds. This material functions independently of the carbohydrate- nitrogen balance or the concentration of auxin. Similar results have been obtained by Stout (16), who observed flow- ering in biennial sugar beets to which reproductive annual scions had been grafted. Additional evidence of this nature has been secured by Banner and Bonner (10) in grafting ex- periments with Ianthium pennsylvanicum and Melchers (15), who made experimental grafts with a number of species. Gholodny (2) postulated that chemicals endowed with the properties of growth substances might be introduced into a plant at different stages of growth and affect its develop- ment. The major emphasis of subsequent studies having to do with testing the effects of introducing synthetic growth substances into plants, were directed at the control of the three phases of reproductive development referred to by Thompson (18) as a) initiation of the flower, b) develOp- ment of the flower, and 0) development of the seed. The observations reported by a number of investigators have given support to the concept that plant develOpment can be controlled by growth'regulating chmnicals. Hitchcock and Zimerman (11) were able to stimulate flowering of Turkish tobacco by applying phenylprOpionic, indolepro- picnic, and indolebutryic acids to the soil. This ac- celeration of flowering was due to the hastening of termi- nal growth after flower buds were famed. Stimulation has also been observed by Galston (8) , who applied 2,3,5-tri~ iodobenzoic acid to soy beans. The treatment augmented the flowering response due to phot0periodic induction but fail- ed to initiate flowers independently. However, Dostal and Hosek (7) were successful in reverting “flower ready“ stem tips of Circaea intermedia to the vegetative habit by ap- plying to them a .25 percent paste of heteroauxin. Similar results were obtained by Zimmerman and Hitchcock (25), who modified the development of tomato buds. Axillary shoots and terminal buds were induced to terminate in flower clus- ters by soil treatments of foliage spray applications of 2,3,5-triiodobenzoic acid. Using Mathiola incana annua (annual stock) as a test plant, Johnson (13) reported that 86% of the plants treated with alpha-naphthozyacetic acid rmained in a vegetative condition while only 6% of the control plants failed to reproduce. The effect of growth substances on flowering, the generation following treatment, has been recently danonstrated by Hitchcockand Zimmerman (12). Dandelion plants were Sprayed with solutions of 1000 ppm 2,4,6—trichlor0phenozyacetic acid and it was found that seed from these plants were significantly reduced in germi- nation, and plants, in turn, grown from the seed were delay- ed in flowering. Thurlow and Bonner (19), in a recent re- port, noted a complete inhibition of the phot0periodic re- sponse of Xanthium by spraying the plants with 500 ppm naphthaleneacetic acid or indoleacetic acid. Initiation of flower primordia in pineapples with ethylene gas was accomplished by Traub (20). In this type of induction there was no change in the amount of auxin and it was concluded that ethylene itself is a hormone. The commercial use of growth substances, for the cen- trol of reproductive deve10pment in plants, has been suc- cessful in the pineapple industry. Clark and Home (3) and also COOper (5) have found that naphthaleneacetic acid can be used to induce differentiation of the pineapple inflor- escence. According to Van Overbeek (21), 2,4-dichlor0phen- cxyacetic acid also hastens flowering but possibly due to the retarding of leaf deve10pment, the stimulation by this substance is not as rapid as that of naphthaleneacetic acid. .His investigations further disclosed that, by the single application of naphthaleneacetic acid, the cabezona variety of pineapple can be made to flower at any time during the year, irrespective of the photOperiod, even under conditions where long days would normally prevent development of primordia. Hewever, van Overbeek (22) further states that continuous treatment with either ethyl- ene or auxins may delay flowering indefinitely. Clark and Kerns (4) and later COOper (5) have shown that flower induction by ethylene may be completely prevented.by subsequent application of auxbn. Continued experimental work by Van Overbeek (23) has indicated that the flower inducing free auxin of the axis evolves from.the bound auxin of the juvenile leaf bases. Origin of the reproductive response from.similar plant parts of celery was determined by Curtis and Chang (6) when they found that the initiation of the floral primordia occurs as a result of the exposure of the ‘young inner heart leaves to cool temperatures. PRELIMINARY TEST WITH NON-EOLTING GOLDEN PLUM]? Mategigls and gethods A preliminary test with celery to determine the vegetative responses and limits of tolerance to growth substances was started in the greenhouse during the fall of 1946. Seed of Non-Baiting Golden Plume (Ferry-Morse, Stock no. 2352) was planted in flats of sand, October 28. . A minimum temperature of 65 degrees was maintained in the greenhouse during germination and the following period of growth. A total of 55 seedlings were transplanted to in- dividual five inch clay pots filled with compost soil, November 25. Two weeks later all pots were fertilized with a solution containing one half ounce of ammonium-nitrate and one half ounce of an all soluble fertilizer having an analysis of 12-5448“ per gallon of water. On January 15, the 55 potted plants were separated into 11 groups of five plants each. Il'he five plants in each group were sprayed with one of the following:** ‘ a) 5 ppm - 2,4-dichlor0phenoxyacetic acid (2,4-D) b) 25 ppm - i a e c) 50 ppm - " " " d) 5 ppm - triiodobenzoic acid (TIBA) e) 200 ppm - " " *Obtained from the Victor Chemical Company, Chicago. ”Grateful acknowledgment is extended to the Dow Chemical Co. , Midland, Michigan for providing some of the chemi- cals used in these tests. f) 500 ppm - triiodobenzoic acid g) 50 ppm - naphthaleneacetic acid (NA) h) 200 ppm - " "- i) 500 ppm - ' ‘ j) 200 ppm - alpha-orthochlorOphenozyprOpionic acid (CLPP) 1:) control (water spray only). The chemicals were applied in aqueous solutions by means of small household sprayers. Particular care was taken to thoroughly wet all of the aerial plant parts. For each chemical, a different sprayer was used, which was free from contamination of other growth substances and was care- fully cleaned between each change in concentration of the material applied. All plants were transplanted to 8 inch clay pots containing compost soil, February 1'7 and moved to the cold frame April 1'7. Minimum night tanperatures in the cold frame averaged 41 3 2 degrees Fahrenheit through May 26. 2,4-D exhibited a striking differential response, depending upon the concentration used. Fifty ppm of 2,4—D produced severe epinasty of the leaves within 24 hours fol- lowing treatment. At this time petioles and edges of the leaflets were curled downward. Ten days after treatment these structures had regained their normal appearance. -10.. (However, the developing leaves emerging from.the terminal cluster began to show formative effects. Many of them deve10ped deeply indented margins which gave them an ap- Vpearance similar to carrot leaves and the stem plate region was surrounded.by a tumorous growth. Seedstalks were first observed on plants treated with 50 ppm of 2,4-D on May 18. Seeding was rapid and the stalks averaged eight inches in height at the time seedstalks began to appear on plants treated with 25 ppm. On August 26 (Figure 1), plants which had received the higher concentration (50 ppm),'were comp pletely mature and the seed had ripened. In contrast, these sprayed with 25 ppm.were only beginning to flower. The lowb est concentration, 5 ppm, produced seed stalks on'a date, may 29, equivalent to that of the control plants. Celery seedlings sprayed with triioddbenzoic acid (TIBA) responded in an entirehy different manner from.those treated with 2,4-D. lPlants did.not exhibit any epinastic or formative effects. .However, in the group which had been sprayed with 500 ppm.of this substance, one plant began de- veloping a seedstalk May 12. The remaining four had become reproductive by May 18. The other concentrations of TIBA produced seedstalks on an average date offlMey 29, comparable to the time of bolting in the control plants. Naphthaleneacetic aeid.(NA), in the concentrations used did not significantly influence growth or development of treated plants. Some activity was observed where a solu- .Enn on .30." “an on . at £05.90 mega 3%»de aogdm no.0 Hoe $5238.82 no hinges go one.» no 33.5 .H .wah -12- tion of 500 ppm caused a definite upward curvature of peti- oles in such a manner that they partly enfolded the heart of the plant. This curvature was very temporary and within 72 hours normal growth was resumed. A11 concentrations of NA produced seedstalks at a time comparable to the controls which began to bolt May 29. Only one concentration (200 ppm) of alpha-orthochloro- phenoaqpmpionic acid (CLPP) was used. It had no observable effect upon vegetative or reproductive deve10pment of the celery plants under the conditions of this experiment. LIED WWTS ggerg Methogg Plants were started by sowing the celery seed in flats of sand and the young seedlings transplanted, when the first true leaves appeared, to three inch clay pots filled with compost soil. Supplementary feeding with a nutrient solution, containing one half ounce of ammonium- nitrate and one half ounce 12-54-18 (100% soluble) per gallon of water, was given all plants March 18. Plants designated to receive reproductive induction were exposed to low temperatures in the cold frame, while plants which were to receive no induction were retained in the greenhouse. The plants were transplanted on May 26 to a well drained and fertilized muck soil, having a pH of 6.8. They were later sidedressed with sixty pounds per acre of ammonium-nitrate June 4 and with eighty pounds per acre of 6-12-12, July '7. The experimental design of the plots is indicated in Figure 2. The two experiments were laid out adjacently, with the ten plants in each treatment being separated into two sections, each section containing five plants of one treatment. One of these sections was planted in such a manner as to constitute one replicate for all treatments while the other section was planted in the same sequence and represented the second replicate. For a given chemical treatment, two additional replicates making a total of four, were in each case provided since ea enspmuemeoa NON mum Ham Hmm Hum Hem HUN Hem Hem HH Ham Ham Ham Ham Ham Ham mam mam mmm mum mom mam .mpeeeanomuo caofiu no gnaw meanneam .m shaman .eepeeae no“ no: ma HH peasanomwu peasanemum mam mam mmm men mom men men mam mam Ham Ham Hmm mem mam mam Ham Ham Hmm Hum Hem aem Hem Ham Ham Ham Hem Hen Hem flow as» mam mam mmm mum mem mem "H802 Nan mnn mum «on men men men Han awn Han Hana Han HAGH fined Hand Hama Head Hana Han Hand Hana Heed area Hana Hana pnosnsenp enooom pnospsenp amnah .N .H "unreasonp no asap mopnoduea send ansOh meta mesa mead mend mend mesa mane mama mead meea mend meea mega meea Heme Hana emsonnooau assayedoo ”enspsnomaop on» mopeoaesu macaw e no sea“ omega .9 .s ma omen so copmaa m4..a «antennae» seamedeea esonw a He sup“ esoeem Hmomsm mnapaodeoz gin .n 0H HHenHoo .m eaeam menace maaeaem-aom .H anem Harm deem seam deem deem Heem deem Heem Heem Henm Haem mama mend mama mama mnem memm meam mamm meem meem meem meem menm meem deem deem Hnwm deem anem Haem H peasanooufl Head Heme Hana Hand Head Heed Hana Hana mpem mnnm mamm mnwm mnem mnem mpem menm mend Need «mod Need wand Need HDaH Hana Han HQHH Aged Heed HDOH Hand Hama Head Heem deem deem deem mama mend mama meme mama mama mane mend mama meme mega mama anw .medm deem deem Hnmm Heum Heem anem Hpem deem seem seam seam Hemm Heum deem "hpoanmb mopmoaesa enouw e no nova pmhuh mnmm mnnm mnmm mnum mnem mnem meem mpem mnam meam menm mnmm meem meem meem meem -15- equal numbers of plants (10) were given cold induction (cold frame) and warm temperature eXposure (greenhouse), respectively. Plants were set eight inches apart in rows which were spaced at a distance of forty-two inches. Growth substances were applied inthe same manner as was used in the preliminary experiment. The following series of chemicals with their respective concentrations were applied at various times in the field experiments: a) 5 ppm - 2,4-D . 1:) 501mm- " c) 50 ppm.- TIBA d) 500 ppm.- " e) 50 ppm.- NA f) 500 ppm - " g) 100 ppm.- CLPP h) 500 ppm - ' 1) control (water spray only) The first treatment was made with plants which had three true leaves and were 4 inches in height (Figure 5). When Spraying in the field, a rectangular wooden frame, twenty inches high, was placed around each plot to eliminate drift to plants of other plots. diam see on nee. eopmohp mnaaeoom no mobmoa oMHanonnmo was 535.5 msoaoag. .353. w .9: .soapmogmne pupa.“ go as: an mpnman Ho omam .390: n .mfin. ao' . a o.\ . L e . dqvm .‘ .0 o . a e -17- merimgt I This emperiment was desigled to determine the in- fluence of various concentrations of growth substances ap- plied at different dates to varieties differing in their susceptibility to premature seeding. .By growing some plants continuously at a relatively high temperature, the author hOped to determine if some of these substances would stimr ulate flowering. Cornell l9 (FerryéMorse, Stock no. 06313) ‘was selected to represent the early high quality types which most often produce seedstalks prematurely. NeheBolting Gol- den Plume (FerryéMorse, Stock no. 2552) was also selected because it is particularly resistant to premature seeding. Seed of these varieties was sown in the greenhouse, January 28. The young seedlings were transplanted March 5 and held in the greenhouse at a.minimum.night temperature of 60 t 1 degree Fahrenheit. On April 4, the potted seedlings were selected at random.and arranged in nine groups of twenty plants each. The spray treatments were then applied according to the plan already outlined for chemicals and concentrations. Thirty-six hours following treatment, half of each group were removed to a cold frame where the plants were exposed to A minimum night temperatures of 41 1 2 degrees Fahrenheit. The other half remained in the greenhouse at the night temperature of 60 1 1 degree Fahrenheit. On May 26, both lots were transplanted to the field. At the same time ninety -18- plants from the greenhouse and ninety plants from the cold frame reserved for field treatment, were also planted in the experimental plot . meriment I; The plan for this experiment was essentially the same as that in Experiment I. However, 0&1. Non-Bolting Pascal (Angler and Musser, Stock: no. 69511) was substi- tuted for Non-Bolting Golden Plume and only plants which had been exposed to low temperatures were used. Seeds were sown in the greenhouse February 16 and the young seedlings were transplanted to 3 inch pots, April 6. These were held at an average night temperature of 60 i 1 degree Fahrenheit. All of the plants were moved to the cold frame April 14, where the minimum night temperatures were 46 1 2 degrees Fahrenheit. The potted seedlings, selected at random, were arranged in nine groups of twenty plants each and sprayed May 2, as previously described. Field planting of these seedlings and ninety other seed- lings as yet untreated was completed June 1. These ninety seedlings were sprayed June 6, according to the plan of treatment outlined under general methods. -19- Res t th Cornel 19 In all treatments of Cornell 19, with one note- worthy exception, seedstalks deveIOped freely within a short time after field planting. On July 1, bolting was clearly evident on control plants from.the group of treat- ments exposed to low cold frame temperatures. In Experi- ment I, these plots which had not received any chemical treatment were bolting 100%1by August 21 (Figure 5). In sharp contrast to this prolific'bearing of seedstalks on the controls, plants sprayed with 100 ppm.of CLPP and sub- sequently exposed to the same low temperatures as the con- trol plants, remained in a completely vegetative condition throughout the season (Figure 6). The chemically treated plants deve10ped full hearts and possessed all the desir- able qualities of a.marketable celery. Similarly, seeding on the control plants grown in the continuously warm envirh onment of the greenhouse, before field planting, began.Au- gust 20. 'fihen plots were noted September 30, 80% of this group had bolted. Again, without exception, those plants which had received the spray of 100 ppm.CLPP; yet other- wise identically treated showed no evidence of a transition to the reproductive stage of development. Companion treat- ments of plants grown in the cold frame and sprayed with 500 ppm.CLPP produced seedstalks in 80% of the plants. This concentration of CLPP sprayed on plants grown under wanm -20- conditions did not effect the number of plants which be- came reproductive. Furthermore, applications of CLPP (Experiment II), after plants had been exposed to low temperatures favorable for induction of seedstalks, did not influence the number of plants which bolted, regard- less of the concentration employed. The growth of seedstalks was clearly influenced.by 2,4-D, when this chemical was applied in a concentration of 50 pp . In Experiment I, where this treatment was ap- plied before the low'temperature induction (Figure 7) or in the field afterward, weekly measurements revealed that the growth increments reach.a.maximum.one week before those of control plants. The formative effects of this concentration of 2,4-D were essentially the same as those observed,in.NOn~Bolting Golden Plume. e t No - olt d Plants of this variety failed to produce seedstalks irrespective of the chemical treatment or temperatures of early growth. However, the leaves of plants sprayed with 50 ppm.of 2,4-D showed epinastic responses similar to those observed in corresponding treatments of the preliminary axe periment. This higher concentration of 2,4-D again promot- ed the development of carrot-like leaves and tumorous grow» ths in the region of the stem.plate (Figure 4). Such tu- mors were associated with a greater enlargement of the stem 1.... . -0- .uxaapmeoom «o eofiposeee Hanson» eopaooon use noses ma Haoanoo no nausea Hosanna .n .mHm new sneeze some» opoemv gushed.“ no nowpodeew define up one whoeoe m .Aew pmsmse ewes» opoem. ego eo see ooa apes amputee ma flamenco ,. _ . A .o .wfie ‘ x e. ,\\. - . e ,u . .. _.\ giflwolziiaflflt hr . V}; l . § ‘. . . . ’ . j \ . xn _ a. . 3 .. r . as c ‘ ‘ . .G .x.» d A . I 1 4. . \. . -. 9/ . .1 ... . :H . \“ . . e . ,4 I . o . v u , . . a p ‘ . . . e I . . .v . w; t a e .. end... a . A 4 . a . . ‘ sl . ... . _ . . luv . ,. .2 ,.. . a . . . .. . .. \ . l _ . u . . A . ' . . e n . v y l . . . \ ‘ . 4 t. . . . i (. v i . .p . . e . . . , . . I I . . -23- plate and appeared to stimulate the development of addi- tional leaf stalks (Figure B). §es_u_lts With 93;, flop-golfing Eagcgl Records of this pascal type were incomplete as a re- sult of tip burn and'black heart which.made it impossible to secure adequate measurements. .HOwever, all normal plants produced seed stalks and there was no indication that one treatment affected plants in a.manner different then any other. 0-“ x§ CONTROL ~- 3 ”M 2 \_._ .‘7 (B. . 5 .p y a. .. ..} w . 1. . A , .. Ant . -. V a . \ . a urdun . .. .1. . r I . i t . J» T 9 - n . . u .- l l , . . I .. .. \» e . .Q, A, a ., a . D, {V r . f . . . . ._ n u . r r . . n . y u :1. . u . 4838 £380 diam sea on $3 season» 358 538 mfifloméoz .m .3.“ W The variety of celery, Cornell 19, which is par- ticularly susceptible to premature seeding, was prevented from seeding when the seedlings were sprayed with 100 ppm of CLPP thirty-six hours before exposure to cool tempera- tures. These seedlings produced normal marketable celery with no apparent reduction in growth or malformations of the plant structures. This indicated that general stunt- ing and consequent delay in maturity was not responsible for the inhibition of the seedstalk development. Microscopic examination of the heart area at the end of the growing sea- son revealed that no floral primordia had been developed. The same concentration of this chemical when applied after thermal induction had an Opportunity to take place, failed to influence subsequent flowering. In view of the evidence presented above, it seems reasonable to conclude that the inhibition of the formation of floral primordia was due to the activity of CLPP in counteracting the effect of sub- stances associated with thermal induction ('florigen'?), which normally would initiate the reproductive stage of development. ‘ The differential response of reproductive structures to varying concentrations of 2,4—D and CLPP was rather con- si stat throughout the experiment. Since each plant in all treatments was completely covered with spray, it is probable that a certain amount of water would be required to wet a given plant. The amount of chemical that any one plant re- -27- ceived would then vary with the concentration of the solu- tion and the area of the leaf surface. The two plants of Cornell 19 which failed to bolt when treated with 500 ppm of CLPP could have conceivably received an amount of chemi- cal equivalent to the amount the plants treated with 100 ppm.received. Van Overbeek (21) has demonstrated that the control of flowering in pineapple depends upon the total amount of chemical the plant absorbs and not directly upon the concentration of the spray solution. The stimulation of flowering by 2,4—D on one hand and the retarding of flowering by a different concentration of that material, on the other hand, has also occurred in pineapples (5), and has been Observed by the writer in flax. The actual mechanism which is responsible for this differential response has not been explained. Hewever, since seed- stalks which.may be stimulated by 50 ppm.of 2,4-D arise at the same time as those of control plants, it is prObable that the increased rate of growth is due, prim- arily, to an increased rate of elongation of the type reported by Hitchcock and Zimmerman (ll). Premature seeding of celery is a major problem in such areas as Michigan, New York, and California where it is frequently exposed to cool temperatures when the plants are young. The crop, normally biennial, responds as an an- nual and produces seedstalks the first year. Celery, which responds in this manner, is of no commercial value. A suc- cessful method for controlling this early seeding is very desirable. Growth regulating chemicals have been reported to influence reproduction in such crOps as pineapple, and a series of experiments were set up to determine their ef- fect upon the reproductive response in celery. The fol- lowing chemicals were applied in aqueous solutions by means of small household sprayers, at the concentrations indicated: a) 5 ppm - 2,4-dichlor0phenoxyacetic acid (2,4-D) b) 50 ppm - " " c) 50 ppm - triiodobenzoic acid (TIBA) d) 500 ppm - " " e) 50 ppm - naphthaleneacetic acid (NA) f) 500 ppm :- " _ " g) 100 ppm - alpha-orthochlorophenoxypropionic acid (cm) h) 500 ppm - " " Treatments were applied to Cornell 19, a variety which is -29- very susceptible to premature seeding, and to the more re- sistant varieties, Non-Bolting Golden Plume and 0&1. Non- Bolting Pascal. Applications were timed with reference to the period when plants were exposed to low temperatures, in such a manner that one group was sprayed 48 hours preceed- ing exposure to cool growing conditions. .A second group received treatment two weeks after plants had been moved to the cold frame and a third group, two weeks after field planting. Simultaneous tests were made on plants which~ were not subjected to low temperatures. Seedstalk development was completely inhibited in plants treated with 100 ppm of CLPP, forty-eight hours'be- fore these plants were exposed to low'temperatures. This material did not influence reproductive growth when applied at any other time or at any other concentration. Fifty ppm. of 2,4—D increased the rate of seedstalk elongation and some evidence was found that 25 ppm of 2,4-D retarded elon- gation. Additional experiments are necessary to establish CLPP as a.means of preventing premature seeding, and to ob- tain more information with respect to variety response, time of treatment, and concentrations required. Howfiver, the results obtained in this investigation indicate that CLPP at a concentration of 100 ppm.may provide a practical method for control of bolting in celery. 6.. '7. 8. 9. 10. 11. 12. ITERATURE CITED CaJlachJan, M.C. Concerning the hormonal nature of plant deve10pment. 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Science 102: 521. 1945. Van Overbeek, J., de Vazquez, S., and Gordon, A. Free and bound auxin in the vegetative pineapple plant. Amer. Jouro Bat. 34: 266-270. 19470 Whyte, R.0. CrOp Production and Environment. Faber and Faber Ltd., London. 372pp. 1946. Zimmerman, P.W. and A.E. Hitchcock. Flowering habit and correlation of organs modified by triiodObenzoic acid. Contrib. Boyce Thompson Inst. 12:491-496. 1942. ROOM 70350 N I -.' . \ >l ' , '\ i I' i \ II 1 ’ ~ \ . v I . v H Nu ,.r' Aug 10 w: "~ 31. ‘1 a we; - H Us: 10. '49 ' $1125 "3 9 Q‘ . 5,. 1;"; l 21! f: .» , lu‘r