HARDENING PROCESS IN PLANTS AND DEVELOPMENTS 

 FROM FROST INJURY ' ' 



By R. B. Harvey 



Assistant Pharmaco gnosis f, Office of Drug-Plant, Poisanous-Plant, Physiological, and 

 Fermentation Investigations, Bureau of Plant Industry, United States Department of 

 Agriculture 



INTRODUCTION 



Hardening plants to resist fiost injury is a well-established practice. 

 The physiological basis for this practice and the mechanism of frost 

 injury have formed an interesting chapter in plant physiology, for it 

 seems that the more commonly understood physical phenomena play an 

 important r61e in determining the resistance of plants to frost. In the 

 resistance of a plant to freezing the relative importance of such factors 

 as undercooling of the tissue, the freezing point of the cell sap, and the 

 precipitation of proteins is much disputed, owing probably to the fact 

 that different plants have been investigated by the various authors. 



In the investigation reported in this paper experiments were made 

 to determine the physiological changes found to occur under this treat- 

 ment in such plants as cabbage (Brassica oleracea capitata), and tomatoes 

 (Lycopersicon esculentum) . 



The method of hardening commonly used is to expose the succulent 

 plants in coldframes for a week or more to temperatures somewhat 

 above the freezing point. 



REVIEW OF LITERATURE 



The mechanics of the process of ice formation within tissues have been 

 investigated by Duhamel and Buffon {9)} They ascribed frost injury to 

 rupture of the cells by growing ice crystals. Goppert (12) and Sachs 

 {42, 43), however, found that ice formation takes place mostly in the 

 intercellular spaces, and hence rupture of the cells does not cause injury 

 from freezing. Miiller {37, 39) reported that ice formation within the 

 cell takes place only on rapid cooling and that ice formation within the 

 tissue was necessary to produce a true frost injury. Wiegand {48, 49) 

 observed microscopically the point of first formation of ice crystals and 

 their increase in size in the intercellular spaces. 



1 In the latter part of 191 5 the work here presented was undertaken at the suggestion of Dr. R. H True, 

 Physiologist in Charge of Plant Physiological Investigations, to whom the writer owes much for advice 

 and direction. The writer i,s also indebted to Dr. WiUiam Crocker, Dr. S. H. Eckerson. Dr. F. C. Koch, 

 and other members of the faculty of the Hull Biological Laboratories of the University of Chicago for 

 instruction and for the use of equipment at that institution. 



2 Reference is made by number ( italic) to " Literature cited," p. 108-ni. 



Journal of Agricultural Research, ^'"' ^^'- '^o- ' 



Washington. D. C. ""^t- "»• '9''* 



p. Key No. 0-158 



(83) 



