Murneek — 89 — Nutrition and Metabolism 



lationship concept should be mentioned here. It has been cited on many 

 an occasion that a relative increase in carbohydrates over nitrogen in some 

 sort of C-N relationship, causes a plant to shift from the vegetative to the 

 reproductive state. This despite the fact that the proponents of the idea 

 have failed to define what particular carbohydrates and what form of 

 nitrogen have this specific dynamic function and what is really meant by 

 the "relationship." For lack of a better procedure, data for determined 

 carbohydrate and nitrogen compounds have been expressed by most in- 

 vestigators by way of ratios. 



In the chemical analysis of the Biloxi soybean plants that had been 

 grown under relatively short photoperiods and, therefore, made reproduc- 

 tive, the writer has expressed, for the stems, the various analyzed carbo- 

 hydrate fractions, using hexose sugars as the basis, and total nitrogen, in 

 the form of ratios. The results are presented in table 4. 



An inspection of the records will show that at the age up to 12 days, 

 when the photoperiodic induction was completed in the short-day plants, 

 the carbohydrate-nitrogen ratio of the stems, at the nodes of which floral 

 organs were initiated, was still lower in the short-day (reproductive) than 

 the long-day (vegetative) plants. The difference undoubtedly was caused 

 by reduced photosynthesis under the shortened photoperiod. Only be- 

 ginning with the 20th day, when photoperiodic inhibition had manifested 

 itself in the short-day plants, the Ch-N ratio began to increase, for now 

 very much less food material was used for vegetative extension. Thence 

 forward inhibition in stem elongation of the short-day reproductive plants 

 became more or less permanent, carbohydrates accumulated rapidly and 

 were stored chiefly in the form of starch. As a consequence, and in spite 

 of some increase in nitrogen concentration also, the CH-N ratio for the 

 stems of reproductive plants increased rapidly. It is quite clear then that 

 the initiation of sexual reproduction preceded the accumulation of carbo- 

 hydrates and the increased Ch-N ratio. Previous to the referred studies and 

 since then much additional evidence has accumulated that carbohydrate- 

 nitrogen changes in plants are not fundamental to flower initiation ( Mur- 

 neek, 21; LoEHWiNG, 12, 13). Without considering any hypothetical 

 "relationship," they are of significance, however, in connection with flower 

 development and performance and the growth of fruit and seeds. 



While considering the bearing of nutrition and metabolism to sexual 

 reproduction, whether this be induced by the photoperiod or other environ- 

 mental factors, one should be aware not only of growth inhibition, whether 

 photoperiodic or otherwise (17, 18, 24), but also the recently disclosed 

 periodic stimulation of growth, which seems to be associated with two 

 phases of reproduction (Wittwer and Murneek, 33; Wittwer, 32). 

 The first apparently occurs during synapsis (union of chromosomes) the 

 second, and probably more effective one, during syngamy (union of nuclei 

 at fertilization). By disbudding, defloration and defruiting experiments, 

 Wittwer (32) has demonstrated that a period of renewed growth follows 

 each of the above important phases of sexual reproduction. Two maxima 

 in growth rate were observed following gametophyte and embryo inception. 

 They were caused probably by the secretion of a special hormone (s) or 

 plant growth substances during the two crucial phases of reproduction. 



