350 PLANT GROWTH SUBSTANCES 



extraction conditions six crystalline substances have been secured. These 

 are being termed florigens as they have been extracted from flowering 

 plants and are not obtained from nonflovvering plants. Partial charac- 

 terization under the direction of Dr. Ben Aycock of the department of 

 Organic Chemistry of the University of Wisconsin indicates that they 

 are mineral salts of fatty acids. Poor solubility makes identification and 

 the determination of physiological activity slow, but observations to 

 date indicate that information, which may answer the question of the 

 nature of the mechanism of photoperiodism, will be obtained from a 

 knowledge of the chemical nature of the extracts now available. 



REFERENCES 



1. Cajlahjan, M. Ch., Compt. Rend. {Dol^ady) Acad. Set. USSR, 18:607 



(1948). 



2. Crafts, A. S., Plani Physiol., 21:345 (^946)- 



3. Melchers, G. and Lang, A. Biol. Zentralb., 67:105 (1948). 



4. Struckmeyer, B. Esther, Botan. Gaz., 103:182 (1941). 



5. Zimmerman, P. W., Torreya, 43:98 (1943). 



