WILLIAM S. HILLMAN 



611 



3. 3X I 



E DTA, M 



Fig. 1. Effects of two /;H levels on EDTA inhibition of flowering of Lemna 

 perpusilla 674(j in continuous light. Each point represents a value derived from 

 one culture. See Experimental, A2. Exp. 6-30-59. 



ways appeared, and recalls the scatter noted earlier (8) for "inter- 

 mediate" levels of EDTA. It is thus clear that pH is a major factor 

 in these experiments; the implications for questions of mechanism 

 will be deferred until later. 



3. Experiments on the role of iron. Frequent attempts to reverse 

 the effects of EDTA with calcium, iron, manganese, zinc, and copper 

 levels increased to at least 10 times those normally used, have been 

 uniformly unsuccessful. A consideration of the levels of EDTA re- 

 quired in this system, the known affinities of various chelating agents, 

 and some of the literature on flowering suggested that EDTA and 

 other chelating agents might affect flow^ering through an action on 

 iron metabolism. There is no evidence at present to support this 

 hypothesis directly, but it has proved possible to confirm an earlier 

 report of work wdth Xanthium (15) showing that iron may play 

 a crucial role in photoperiodic induction. 



Preliminary experiments showed that flowering in cultures main- 

 tained under short days with EDTA in the medium could be almost 

 completely inhibited by low iron concentrations which did not affect 

 vegetative growth. Such results indicated a relatively limiting role 

 for iron in flowering, but whether in the photoperiodic induction 

 itself or in subsequent flower development was not clear. Experiments 

 in which cultures are restored to normal iron conditions immediately 



