Vernalization and Photoperiodism — 24 — A Symposium 



ing varying proportions of carbohydrates and nitrogen. A difficulty was ex- 

 perienced in that even on media containing little or no sucrose some degree 

 of vernalization was apparent, and this applied only to a few individual 

 embryos. It appeared that quite small amounts of sucrose were adequate 

 for vernalization and that a source of this sugar may have been available 

 within the individual embryo, either as stored sugars or starch in the tissues 

 or as starch grains adhering to the scutellum. A technique was therefore 

 developed involving periods of starvation for the embryos at high tempera- 

 ture to remove available sugar by respiration and this successfully reduced 

 the variability of the low sugar series, although it raised a further set of 

 problems requiring further investigation. The scope of the eighth study is, 

 however, confined to a consideration of the efifect on vernalization of vary- 

 ing the carbohydrate and nitrogen supply, the effectiveness of various carbo- 

 hydrates in growth and vernalization, and to a discussion of the results 

 obtained "within the limits imposed by the unforeseen difficulties of the 

 experiment." 



The whole question of the auxin production in the developing and ripe 

 ear has been systematically studied and its relation to vernalization has been 

 investigated by Hatcher ( 1945) . This work has experimentally tested the 

 hormone hypothesis of Cholodny and has shown this theory to be com- 

 pletely untenable. Preliminary reports have appeared in Nature (Hatcher 

 and Gregory, 1941 ; Hatcher, 1943). The auxin content was determined 

 by the standard Avena coleoptile test of Went ( 1928) . The following sali- 

 ent points have been established. Mature cereal grains of different species 

 vary considerably in total auxin content and concentration, giving a descend- 

 ing series : maize, oat, rye, wheat, barley. The auxin of the rye grain is lo- 

 cated in the endosperm and chiefly in the aleurone : none could be definitely 

 detected in the embryo itself. The auxin contents of spring and winter rye 

 varieties are not different. The auxin is detectable in the embryo either 

 during development or during germination either at normal or vernalizing 

 temperatures. Auxin, far from being accumulated in the embryo of grain 

 undergoing vernalization as Cholodny supposed, is not concerned in the 

 process. The other findings in this work are not of immediate concern and 

 are therefore very briefly mentioned. 



Free auxin appears in the rye grain in the third week after fertilization, 

 accumulates during the next month to a. peak value and disappears almost 

 completely with ripening. A "precursor" is present similar to that described 

 in maize by Avery, Berger, and Shalucha ( 1941 ) and isolated by Berger 

 and Avery (1944). This precursor releases indole-3-acetic acid on alkaline 

 hydrolysis (optimal conditions N/50 NaOH). The precursor and free 

 auxin appear at the same time and both accumulate to a peak value, up to 

 which time they are present in a constant ratio of 2:1. During ripening the 

 free auxin disappears at a greater rate, so that in the ripe grain of rye the 

 ratio reaches a value of 80 : 1 precursor to free auxin. Spring and winter 

 rye are quite similar in the matter of auxin production. 



When prematurely harvested the same cycle of auxin accumulation and 

 disappearance occurs, but the peak value is the lower the earlier the grain is 

 removed from the plant. No auxin is present in the ear prior to emergence. 



