Whyte — 13 — Research in Vernalization 



where the temperatures were such as to prevent any further progress through 

 the thermo-phase by those plants which had failed to complete this phase 

 in the open. Winter rye failed to ear only after the last date of sowing, and 

 winter wheats after the last two dates. It is therefore concluded that, even 

 in strongly "winter" plants, the thermo-phase may be fully or partially 

 passed during the winter. 



TuMANOV considers that the completion of the thermo-phase alone does 

 not yet necessarily mean that frost resistance is markedly reduced, provided 

 the conditions for subsequent growth are not present. Different conditions 

 arise, however, under a deep snow cover or during a temporary thaw, when 

 plants may resume active growth very readily and would thus have a reduced 

 resistance to frost. Tumanov considers it possible that, after the thej-mo- 

 phase, the growing point is capable during resumption of growth of chang- 

 ing the state of the protoplasm in all other tissues in existence at that time, 

 and suggests a hormonal mechanism as the possible explanation. 



KuPERMAN (1936) produced evidence that vernalized plants accum- 

 ulated much smaller quantities of sugars than unvernalized plants, but 

 Tumanov and Federova found that vernalized plants have sufficient 

 amounts of sugars and that a sugar deficiency cannot be regarded as the 

 reason for their lower frost resistance. The amount of sugars in vernalized 

 plants first rose very slowly and later, in April, more or less rapidly, reach- 

 ing 26 per cent on May 7, or 10 per cent lower than in unvernalized plants, 

 and similar to unvernalized plants before wintering. 



Tumanov and Ivanova found that the exposure of vernalized plants to 

 the conditions requisite for the second phase of hardening had no effect, al- 

 though it is during this phase (of hardening) that plants should show a con- 

 siderable increase in their frost resistance. Tumanov therefore assumes 

 that those changes that originate during vernalization cause the protoplasm 

 to be readjusted in such a way that it loses the ability to undergo the appro- 

 priate changes during the second phase of hardening, regardless of the pres- 

 ence of protective substances, dehydration and low temperatures. 



Since enzymatic processes are very active during the period of germina- 

 tion, it was natural that studies should be made of their behaviour in rela- 

 tion to vernalization. Whether any change which may be noted in their 

 activity is governed ultimately by the concentration of hormones present 

 depends upon the confirmation of Cholodny's hormonal interpretation of 

 vernalization. The studies on enzymes in relation to vernalization made by 

 RiCHTER and his associates and Demkovskii, and on the iso-electric point 

 by RiCHTER, Gavrilova and others, are described in the early reviews of 

 vernalization (I.A.B. 1935). 



Oveckin and others (1936) studied the biochemical changes in winter 

 wheat grains during vernalization. Grains were vernalized at to 1°C. 

 under normal air conditions, and also in a 0.003 per cent concentration of 

 chloroform or ethylene chloride. Samples were taken on every sixth day 

 and records made of respiration rate, sugar content, catalase activity, con- 

 tent of mono-amino-acids and reduced glutathione, and of the percentage of 

 fully vernalized grains that grew when planted out of doors. The presence 

 of chloroform and ethylene chloride reduced the percentage of fully ver- 

 nalized grains ; the respiration rate, catalase activity, and content of reduced 



