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BRIEFER ARTICLES 



443 



To make certain that all of the samples should have ice formed on 

 the surface, a small drop of water was placed on each. To test the effect 

 of the epidermal covering in preventing inoculation, samples of the same 

 material were cooled with the coverings intact, and also after they had 

 been removed. Precautions were taken to prevent the inoculation of 

 the tissue from juices exuded at cut surfaces. In all cases the cut sur- 

 faces were dried and covered with vaseline, which procedure was found 

 to prevent such an inoculation of the tissue. In all the tests it was 



Fig. 2 



found that when thick epidermal coverings were unbroken, undercooling 

 occurred, while in those cases where they were removed but little 

 undercooling occurred. 



Fig. 2 shows typical cooling curves, indicating the importance 

 of the epidermal coverings in preventing ice formation within the tissue. 

 It appears that the tissue without the protective covering is unable to 

 undergo any great amount of undercooling. This depends in part 

 upon the amount of shaking of the tissue. The osmotic concentration 

 or the presence of colloidal substances in solution in the cell sap are of 

 relatively minor importance in determining the undercooling. 



