WILLIAM S. HILLMAN G79 



experiments, strongly support the hypothesis that iron is crucial in 

 photoperiodic induction, and is not related to flowering simply 

 through its role in general metabolism. 



B. Experiments with L. gibba 



The effects of chelating agents on the conditionally short-day L. 

 perpusilla made it desirable to see whether photoperiod-EDTA in- 

 teractions also occur on the long-day L. gibba. The experiments were 

 done with strain G3 except where noted, since its growth on M 

 medium was more regular and rapid than that of the Gl chiefly 

 studied by Kandeler (10, 11). Under the conditions employed, a 

 major interaction of EDTA with photoperiod on flowering was easily 

 demonstrated. 



1. EDTA-pliotoperiod interaction. In exploratory experiments 

 analogous to those possible with L. perpnsilla, cultures of L. gibba 

 G3 were placed under long (24-hour) and short (8-hour) photo- 

 periods in M medium with or without sucrose and with or without 

 EDTA and observed for flowering. The sucrose had little effect ex- 

 cept to delay flowering, and to speed growth in short days. At about 

 the 10th day, depending upon the experiment, long-day cultures 

 with EDTA showed visible flowers and FL% values of about 30; none 

 of the others show^ed any evidence of flowering. By the 15th or 16th 

 day a low FL% value was observed in the long-day EDTA-free cul- 

 tures; no flower primordia were ever observed in any short-day cul- 

 tures even after the growth had proceeded beyond the frond number 

 of flowering long-day cultures. 



Most of these results are simple confirmations of Kandeler's work: 

 no flowering under short days, and none under long days with fluores- 

 cent light until the medium becomes "old." However, the effect of 

 EDTA in promoting flowering was large, and entirely unexpected 

 from Kandeler's observations. Such experiments showed consistently 

 that EDTA added to M medium in concentrations from 3 X lO-** 

 to 10—^ M interacts with long photoperiod to cause rapid flowering 

 in L. gibba G3, flowering which regularly occurs before any primordia 

 are detectable in M medium alone. A systematic investigation of 

 this effect was thus undertaken, using the following standard condi- 

 tions unless otherwise noted: the stocks were grown in M medium 

 with sucrose under 8-hour photoperiods of 600 footcandles of mixed 

 warm and cool white fluorescent light, at a light temperature of 26°C 

 and a dark temperature of 23 °C. Experiments were performed in con- 

 tinuous light of the same kind and intensity at 26°C, using M with- 



