Vernalization and Photoperiodism — 16 — A Symposium 



The experiments of Kostjucenko and Zarubailo are discussed along with 

 those of Gregory and Purvis on the same aspect in a later section of this 

 review. 



Another small point may be mentioned before leaving the Russian re- 

 search on vernalization. It has been found that not all plants can be ver- 

 nalized in the form of seeds or grains, and that the low temperature applied 

 does not begin to have an effect on certain types until a seedling has been 

 formed. This applies more particularly to certain species of Brassica such 

 as rape and turnip. 



Germany: — The name of Professor W. Rudorf of the Kaiser Wil- 

 helm-Inst. f. Ziichtungsforschung, Miincheberg, Mark, is chiefly associated 

 with work on and reviews of vernalization as applied to German conditions 

 and crops. A review of the literature on vernalization was published in 

 1936 (Rudorf and Hartisch, 1936), and a summary of experinaents made 

 at Miincheberg, Giessen, Gottingen, Berlin, Berlin-Dahlem, Heidelberg and 

 Leipzig was published in 1938 (Rudorf, 1938fl). Rudorf himself studied 

 the relation between vernalization and photoperiods and resistance to cold. 



Using winter, dual-purpose and summer forms of wheat and barley, 

 Rudorf (1938^)) applied different temperatures and different photoperiodic 

 treatments with a view to discovering a method of producing material for 

 studying the physiological causes of cold resistance. Resistance to cold 

 under periods of chilling ranging from 20 to 60 days at 3 to 5° C. was deter- 

 mined, and it was found that such resistance is largely governed by the con- 

 dition of the plants in the dormant period before the thermo-phase has been 

 completed, that is, before vernalization is complete. The more this internal 

 condition is degraded by vernalization the less is the resistance to cold. 

 Varietal differences are noted; in certain varieties a reversal in the reac- 

 tion can be seen after 60 days' chilling. It remains a question whether 

 such a turning point can also be determined in definite winter forms chilled 

 for more than 60 days. When the thermo-phase has been partially com- 

 pleted, the capacity to harden is annulled to a degree which is in proportion 

 to the duration of the treatment. The further work which was then stated 

 to be in progress was the discovery of varieties with as long a thermo-phase 

 as possible (maximum requirement of low temperature) and the maximum 

 cold resistance at that phase, and the discovery of varieties which would still 

 exhibit great hardening capacity even after completing the thermo-phase. 



In 1936 Harder and Stormer (1936) showed that white mustard 

 (Sinapis alba) responded to temperature of germination best in short-day 

 conditions. An exhaustive comparative study of vernalized mustard and 

 oats made by von Denffer (1939) under a series of daylengths artificially 

 maintained showed that this different behaviour of these two plant types 

 occurred in the time between initiation of flower primordia and flowering. 

 The relative shortening of the purely vegetative phase from germination to 

 the visual appearance of flower buds in mustard, and shooting in oats, was 

 on the other hand approximately the same for all daylengths (from con- 

 tinuous light down to 12 hour day) as compared with control plants which 

 had not been vernalized. 



The increase in duration of vernalization led in both mustard and oats 



