An Experimental Study of the Rest 

 Period in Plants 



Physiological Changes Accompanying Breaking of the 

 Rest Period 



FIFTH REPORT 

 W. L. HOWARD 



INTRODUCTION 



The object of the physiological investigations described in this 

 bulletin was to secure information on the complex problem of the 

 specific effects produced by anesthetics and other agents employed 

 in breaking the rest period of woody plants. 



The existence of a rest period in plants has been thoroughly 

 demonstrated by a number of investigators. At the Missouri Agri- 

 cultural Experiment Station 1 approximately 300 species of woody 

 plants have been studied and practically all were found to have a 

 rest period of varying duration and intensity. 



Approximately 100 species of herbaceous perennial plants were 

 studied, and, while the number that could be said to have a rest 

 period was not determined, it was thought that from 10 to 25 per 

 cent possessed a resting phase. Numerous experiments with many 

 of our common species of bulbs indicated that all of them are pos- 

 sessed of a pronounced rest period. Investigations covering about 

 200 species of seeds of woody and herbaceous plants yielded the infor- 

 mation that from 50 to 90 per cent passed through a resting phase 

 some time after ripening. 



The rest period in woody plants is not all the same or even anal- 

 ogous to the winter dormant period. In woody plants, such as peach 

 and apple trees, the rest period has been observed to set in as early 

 as May in the peach, and in early June in the apple. These, however, 



1. Howard, W. L., Experimental Study of the Rest Period in Plants. Mo. 

 Agr. Exp. Sta. Research Bulletin 1. 



, Rest Period Studies with Bulbs and Herbaceous Perennial 



Plants. Mo. Agr. Exp. Sta. Research Bui. No. 15. 



, Rest Period Studies with Pot-grown Woody Plants. Mo. 



Agr. Exp. Sta. Research Bui. No. 16. 



, An Investigation of the Rest Period of Seeds. Mo. Agr. 



Exp. Sta. Research Bui. No. 17. 



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