﻿APPLEM AN—REST PERIOD 



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they must be due to internal causes. He does not intimate, how- 

 ever, the nature of these causes. 



It is true that Volkens does not include the factor of salts 

 among the external conditions that may affect the growth processes; 

 and besides, he and Klebs do not seem to have quite the same 

 conception of internal causes, so that their views may not be as 

 antagonistic as first seems. According to Volkens, everything is 

 conditioned by internal causes which cannot be brought into evident 

 connection with external factors. The important thing to Klebs 

 is whether the rest is caused by the outer world or is an expression 

 of an internal fixed " specific structure." Volkens does not dis- 

 criminate between specific structure and internal conditions. It is 

 conceivable that a slight external change may set into motion a 

 chain of effects which would ultimately so change the internal con- 

 ditions of the growing cell or its immediate environment that growth 

 would be arrested and seem to be due to internal specific structure. 



Attempts to shorten the rest period of buds and bulbs by arti- 

 ficial means are numerous and some have been successful. Muller- 

 Thurgau (20) claims to have shortened the rest period of potato 

 tubers by one month's storage at o° C. The use of ether and chloro- 

 form dates from the important work of Johannsen (14), who suc- 

 ceeded by their means in forcing buds to open 3-6 weeks earlier than 

 normally. He found, however, that these agents are effective only 

 at the beginning and near the end of the rest periods. The warm 

 bath has been used successfully in shortening the rest period. 

 Molisch (18) caused an earlier opening of buds by immersing the 

 shoots in water at 35 0 C. Muller-Thorgau and Schneider- 

 Orelli (22) hastened the growth of lily-of-the-valley bulbs and 

 potato tubers by warming them at a temperature of 38 0 C. and 

 maintaining a germination temperature of 26 0 C. Warm air was 

 equally as effective as warm water. In an endeavor to test Klebs's 

 conception regarding the importance of salts in bud growth, 

 Lakon (17) stood cut twigs of trees and shrubs in Knop's solution 

 and found that of a large number only one failed to show an earlier 

 unfolding of the buds than normally. This does not prove, how- 

 ever, that the buds failed to germinate on account of the lack of 

 salts any more than the lack of ether prevented germination in 



