114 • Chemical Control of Flowering 



be higher than that for vegetative growth only. Whether this might 

 be true also for other micronutrient elements in this plant, or 

 whether it truly indicates a special role of iron in photoperiodic 

 induction, is not yet clear. Yoshimura (1943) has reported promo- 



Fig. 6-3. Duckweeds (Lemna) as experimental organisms for the study of 

 flowering under highly controlled conditions. (^1) An aseptic culture of L. 

 perpusilla. (B) A group of L. gibba, showing anthers. (Photographs by Dr. J. H. 

 Miller and Yale University Photographic Services.) 



tion of flowering in another duckweed, Spirodela, by molybdenum 

 deficiency. For a review of other early reports on duckweed flower- 

 ing, see Hillman (1961a). 



The writer has pursued evidence of important metal effects 

 in photoperiodism originating in observations on the effects of 

 chelating agents on the flowering of two species of Lemna (see 

 Fig. 6-3). Chelating agents are compounds that form particularly 

 stable complexes with many metal ions and thus affect their chem- 



