Murneek — 85 — Nutrition and Metabolism 



seem to curtail greatly the diurnal production of carbohydrates, usually 

 leads to initiation of flowers in the case of many short-day plants. 



Nevertheless carbon assimilation may possibly be connected, in one way 

 or another, with the photoperiodically induced stimulus in the leaves. 

 Parker and Borthwick (29) have shown that induction does not occur 

 when plants are deprived of carbon dioxide, without which it may not take 

 place in a leaf even though satisfactory conditions for photosynthesis pre- 

 vailed elsewhere in the plant (Harder and Witsch, 8). When the long- 

 day plant Hyoscyamus niger is submitted to short-day exposure flower 

 induction is inhibited. As this (inhibition) seemed to have occurred in 

 darkness, it suggested to Melchers and Claes (15) that a dissimilation 

 process may be involved which destroys a possible carbohydrate precursor 

 of the flower hormone ("florigen"). This idea was tested further by keep- 

 ing the plants during ^^-% of the dark period in an atmosphere of N2 or 

 CO2. Because of this treatment flower initiation was inhibited, which 

 evidently was in support of their hypothesis. When sugar was supplied 

 by means of leaf infiltration, flowering also occurred under short-day ex- 

 posure. 



Experimental work with Bidens tripartitus has indicated to Potapenko 

 (30) that photoperiodic induction has no direct relationship to photosyn- 

 thesis but that elimination of light during the dark phase seems to "restitute 

 the working capacity of the chloroplasts" so that their assimilation may be 

 enhanced during the following light phase. 



Assimilation and respiration were determined manometrically in leaves 

 of Kalanchoe blossfeldiana under short- and long-day exposures by Bode 

 (2). The reproductive short-day plants had at the time of flower bud de- 

 velopment, higher photosynthesis and respiration rates- Chloroplast pig- 

 ments also increased during the short-day exposure. This is in agreement 

 with some observations made by the writer on short-day soybean (Biloxi) 

 plants (Murneek, 21). It should be of interest to note here that as Biloxi 

 plants become reproductive, as a result of exposure to appropriate photo- 

 periods, there is an augmentation in carotene and xanthophyll contents of 

 the leaves. This may possibly have some connection with sexual repro- 

 duction in this plant (Murneek, 20, 23). 



The idea proposed by Grainger (6) that flower induction is influenced 

 by the rate of nocturnal translocation of carbohydrates from the leaves to 

 the growing points, not only lacks confirmation but is contradicted to a 

 considerable extent by his further studies with Anemone, Epilobium, 

 Lupinus, Lysimachia and Vaccinium wherein he shows that production of 

 flower initials requires very Httle carbohydrates but only "pledge" a con- 

 siderable amount for future requirements (Grainger, 7). 



The writer has conducted extensive investigations on the relation of 

 chemical composition to photoperiodism using several kinds of plants, but 

 chiefly the now popular Biloxi soybean, for this purpose (21). Instead of 

 analysing plants during comparatively late stages of flower formation, as 

 had been done heretofore, he followed their chemical composition, as re- 

 gards nitrogen and carbohydrate content, in various parts throughout the 

 course of vegetative and reproductive development. The plants were grown 

 in rich soil and, beginning on the third day of emergence above ground, 



