Vernalization and Photoperiodism — 84 — A Symposium 



factor in floral initiation as the photoperiod or temperature but that the 

 time of appearance of visible floral buds was altered by it in some species. 

 Parker and Borthwick (28) found that in Biloxi soybeans at the end 

 of the induction period (1 week), the total and soluble non-protein nitrogen 

 concentration was higher in the reproductive than the vegetative control 

 plants. This is a confirmation of the results obtained with the same plant 

 by the writer (21). They state that the differences in chemical composi- 

 tion of plants did not seem to have any causal relationship to flower initia- 

 tion. From their observations of Xanthium pennsylvanicum plants, grown 

 in nutrient solutions of high or low NPK content or with or without an 

 external supply of N, Neidle (26) and Naylor (25) conclude that the 

 amount of nitrogen in the nutrient medium had no definite effect on re- 

 sponse to the photoperiod and that plants low in NPK had the same critical 

 day-length requirements as those supplied amply with these soil nutrients. 

 When given abundant N more burrs were produced on Xanthium plants, 

 however. Similarly a larger crop of seeds was set by guayule plants that 

 received the highest concentration of nitrogen (Mitchell, 16). 



From his sand-nutrient-solution cultures of several kinds of plants 

 Cajlachjan (3, 4) concludes, likewise, that no variation in mineral nu- 

 trition used could change plants from a vegetative to the reproductive state 

 and that contrary to the adopted idea that a large increase in nitrogen supply 

 prevents plants from entering the flowering and fruiting phase, frequently 

 nitrogen stimulates this process. Both long- and short-day plants reacted 

 similarly to nitrogen nutrition. In another experiment, while exposing 

 Perilla nankiensis and Chrysanthemum indicum plants to various photo- 

 periods, he immersed the leaves into .5 and 1.0% solutions of NaNOg, 

 KNO3, NH4NO3, asparagin and glucose, respectively, for one hour every 

 few days and, in addition, applied to the soil nitrates. The results seemed 

 to indicate that, if anything, extra supply of nitrogen was favorable to 

 flowering and that any possible carbohydrate-nitrogen relationship has no 

 bearing on induction of reproduction (Cajlachjan, 5). Considering the 

 above cited and much other evidence, it appears that nitrogen is one of the 

 most crucial nutrient elements in initiation of sexual reproduction and that 

 it often is a limiting factor in the production of fruits and seeds (Mur- 

 NEEK, 17, 19). 



One is reminded here of Klebs' experience with Sempervivum funkii 

 plants, which would not flower in winter and lead him to remark that "aber 

 niemals gelang es Bliiten im Winter zu erzeugen, obwohl die bliihreifen 

 Rosetten bereits im Herbst alle notigen organischen Staff e aufgespeichert 

 enthalten." By exposing the plants for a few days to continuous electric 

 light (increase in length of day) they produced flowers, while quite similar 

 non-exposed plants, kept in the same greenliouse, did not bloom (Klebs, 

 10, p. 27). 



Photoperiodism, as regards the induction of reproduction, does not seem 

 to stand in any direct quantitative relationship to carbon assimilation for : 

 a) It may occur in very weak light, which does not permit much photo- 

 synthesis and during which respiration probably is in excess of carbohy- 

 drate synthesis, b) Drastic reduction in the length of day, which would 



