Vernalization and Photoperiodism — 86 — A Symposium 



Table 1 : Changes in total nitrogen content of soybean plants, vnr. Biloxi: — 



Percentage on Dry Weight Basis 

 Age — Days Stems Leaves 



Long 



6 8.15 



12 6.44 



20 3.73 



27a* 3.33 



33b 3.04 



40c 2.75 



80d 1.55 



* o — Flower buds on short-day plants. 

 b — Flowers on short-day plants. 

 c — Flowers and small pods on short-day plants. 

 d — Pods of various sizes on short-day plants. 



exposed respectively to long (14 hour) and short (7 hour) photoperiods. 

 Results of analyses of stems and leaves are presented in table 1. 



It will be observed that the short-day or reproductive plants, while 

 growing in the same soil medium, had a considerably higher nitrogen con- 

 centration from the time of inception of floral primordia (sixth to twelfth 

 days) till flowering and even during early fruiting. This was true of both 

 the leaves and stems, but particularly so of the latter. This is in agreement 

 with the results reported by Knodel (11), by Asami and Ito (1) and sub- 

 sequently by others (Parker and Borthwick, 28). 



The augmented nitrogen content of the short-day plants, in comparison 

 to the long-day ones, was due to an early and continued inhibition of their 



Table 2 : Rate of stem elongation of soybean plants, z'ar. Biloxi. Height in 



centimeters: — 



Age, in Days 



2 

 6 

 12 

 20 

 27 

 33 

 40 



growth in height (photoperiodic inhibition), as is evident from table 2. 

 On the 12th day the plants were already measurably shorter in stature. As 

 vegetative growth is curtailed, and no impediment in absorption of soil 

 nutrients and in organic synthesis, nitrogenous and other compounds ac- 

 cumulated in the plants. That there was an accretion of carbohydrates, 

 especially starch, similarly to nitrogen, is shown in table 3. The plants were 

 exposed to the respective photoperiods, as was stated before, on the 3rd 



