Vernalization and Photoperiodism — 22 — A Symposium 



in Studies 2 (Gregory and Purvis, 1938a), a loss of vernalization by dry- 

 ing down the vernalized grain for periods longer than 6 weeks is demon- 

 strated by experiment. Although the effect of flowering vanishes, an after- 

 effect is shown by the high tiller production ; this is attributed to a reversal 

 in the hormone synthesis noted (as indicated in the diagram above). 

 This line of approach was continued in Studies 3 (Gregory and Purvis, 

 1928b) when anaerobic conditions were utilized to inhibit growth by means 

 other than low temperature. This made possible a successful experimental 

 demonstration of a quantitative reversal of the vernalizing effect of low 

 temperatures by higher temperatures, as well as the complete inhibition of 

 the low temperature effect in the absence of oxygen ; and definitely proved 

 that low temperature and not mere inhibition of growth is the essential factor 

 in vernalization. 



Continuing the study of the part played by the various tissues of the 

 grain in the process of vernalization, Gregory and De Ropp ( 1938) found 

 that in the absence of a carbohydrate supply the isolated embryo cannot be 

 vernalized by low temperature. Also it should be noted that previous to the 

 excision of the embryo in the work of Gregory and Purvis the grain had al- 

 ready been soaked in a sterilizing solution for a period of 5 hours. De Ropp 

 (1939) therefore studied more closely the conditions obtaining in the grain 

 during the first few hours of germination, and found that, during the pre- 

 liminary soaking, a "regulator" controlling its auxin production and dis- 

 tribution enters the embryo from the endosperm and aleurone layer. 



The fifth Study in this series from the Research Institute of Plant 

 Physiology concerns an investigation by Purvis (1939) on the inheritance 

 of the spring and winter habit in hybrids between Petkus winter rye and 

 Petkus spring rye. This is thus outside the strict terms of reference of the 

 present review. The cross gave an Fj generation in which the spring habit 

 was completely dominant, while in the F2 germination the spring and winter 

 plants were in an approximate 3 : 1 ratio. In the F2 generation, however, 

 there is within the "spring" and "winter" classes a dispersion of flowering 

 dates, suggesting a less simple inheritance. Purvis explains this on the 

 basis of independent segregation of factors for early and late ripening as 

 distinct from the spring and winter habit. The Russian interpretation of 

 results such as these is discussed elsewhere by Whyte (1946). 



Returning again to the question of the nature of the biological processes 

 occurring within a vernalized grain, Nutman (1939) investigated by cyto- 

 logical technique the processes occurring in the embryo-sac of rye subse- 

 quent to fertilization ; an aspect of direct interest in connexion with the fact 

 that vernalization can be carried out on a developing embryo (see later sec- 

 tion of this review). It was hoped to obtain some indication of the functions 

 of the various tissues of the developing fruit and to throw some light on 

 the possible role of hormones in development. This study has led to the 

 discovery of new facts hitherto overlooked, more particularly the part 

 played by the nucellar tissue in the organization of the mature grain and a 

 sequence of degenerative changes associated with each phase of develop- 

 ment. Nutman considers the possible role of nekrohormone (or wound 

 hormone) in the development of the rye grain, comparing his observations 



