Flowering 261 



measurable as greater numbers of flowers and the differentiation of 

 the first flower at a morphologically earlier stage. The large gains in 

 numbers of flowers and in earliness following auxin and low tempera- 

 ture treatments are consistently obtained in winter greenhouse con- 

 ditions, but not always in summer field conditions of optimum 

 sinilight and temperature. Some compounds which are not auxins, pro- 

 duce the same effect, and it appears to be related to some physiological 

 process which is dependent upon carbon dioxide, presumably a non- 

 photosynthetic fixation process (Leopold and Guernsey, 1954). 



The method by which these treatments are applied has been 

 worked out primarily by using naphthaleneacetic acid. Soaking seeds 

 for twenty-four hours in solutions of from 0.01 to 1 mg./l. produces 

 gains in earliness if followed by temperatines of 3 to 10° C. In Alaska 

 pea the low temperature incubations may be terminated in four days, 

 whereas in the tomato, the low temperature incubation must proceed 

 for about two weeks (Guernsey and Leopold, unpublished). A wide 



0.0001 0.001 0.01 0.1 I MG/L 



CONG. OF AUXIN 



Fig. 107. The modification of flowering of Biloxi soybean by the treatment of 

 seed with auxin (naphthaleneacetic acid) followed by a two-week incubation at 

 3° or 18° C (Leopold and Guernsey, 1953). 



