Vernalization and Photoperiodism — 88 — A Symposium 



the end of the induction period, considering most of the flower initials. 

 Assuming this to be the case, and considering observations on other plants, 

 growth in height then may be inhibited during at least the following stages 

 of sexual reproduction: a) While floral primordia are initiated {Soja, etc.), 

 b) while the plant is in full bloom {Zea, Triticum, Cucumis, etc.) and c) 

 during the period of fruit and seed development (Lycopersicon, Cucumis, 

 etc.). 



In all instances it is the reproductive organs, in one stage of develop- 

 ment or another, that seem to control metabolism and growth of the plant, 

 once a state of intense reproduction is initiated and environmental condi- 

 tions are favorable for its maintenance. Since plants that have become 

 highly reproductive require large amounts of food for seed and fruit de- 

 velopment, and as these substances are used also for the formation of 

 vegetative tissues, though not necessarily in the same proportion, one can 

 see the value of a mechanism in the plant that would lead to curtailment of 

 vegetative growth and consequent diversion, storage and supply of certain 

 materials for the growth of embryos and accessory structures (Murneek, 

 22 ; LoEHWiNG, 13 ; Wolfe et al., 34 ; Novikov, 27) . 



Table 4 : Carhohydrate-nitrogen relationships (ratios) in stems of soybean plants, var. 

 Biloxi, when groivn under certain photoperiods: — 



Sugar 

 AND Total 

 Sugar Starch Starch C-h* 



Description of Plant Material N N N N 



Plants 2 days old 



Before exposure to photoperiod. Whole stem .42 .48 .90 3.25 



Plants 6 days old (2 + 4 days) 



Long-day, height 10 cm. Whole stem 31 .26 .57 2.61 



Short-day, height 10 cm. Whole stem 26 .12 .38 1.40 



(Beginning of induction of reproduction.) 



Plant 12 days old (2 -|- 10 days) 



Long-day, height 17 cm. Whole stem 29 .18 .47 2.15 



Short-day, height 17 cm. Whole stem 18 .21 .39 1.36 



(Induction probably completed.) 



Plants 20 days old (2 + IS days) 



Long-day, height 24 cm. Whole stem 46 .31 .77 3.33 



Short-day, height 20 cm. Whole stem 14 .26 .40 3.34 



(Primordia formed, but no visible flower buds. 

 Growth inhibited.) 



Plants 27 days old (2 + 25 days) 



Long-day, height 32 cm. Whole stem 35 .10 .45 4.50 



Short-day, height 2! cm. Whole stem 34 .30 .64 4.68 



(Flower buds distinct.) 



Plants 33 days old (2 + 31 days) 



Long-day, height 41 cm. Whole stem 1.17 1.07 2.24 7.72 



Short-day, height 23 cm. Whole stem 47 2.72 3.17 7.22 



(Buds, flowers and small pods.) 



Plants 40 days old (2 + 38 days) 



Long-day, height 47 cm. Whole stem 1.27 2.20 3.47 10.82 



Short-day, height 24 cm. Whole stem 1.35 6.25 7.60 13.60 



(Buds, flowers and pods up to 4 cm.) 



* C.h refers to total carbohydrates or the sum of total sugars, starch and hemicelluloses. 



While it would seem to be quite obvious that the initiation of reproduc- 

 tive organs is the function of some as yet unknown hormone (s) and not 

 caused by the nutritional state of the plant, the carbohydrate-nitrogen re- 



