167 



Fig. 26. Drawings 1 to 7 : Transformations in epidermal plant cells while 

 in the frozen state. (From Luvet and Gibbs, 1937.) Drawing 8: thawing 

 cell. In all the drawings, the fluid sap is represented in black and the ice 

 in white. 



be observed and for some metals, the degree of ductility 

 and malleability can be related to the number of gliding- 

 planes ((■/. Tammann, 1925, p. 192, sqq.). Even the classi- 

 cal experiments known as "regelation" in which a piece 

 of ice gives way under the pressure of a wire applied on it, 

 should perhaps be explained, at least partly, by the gliding- 

 motion of the crystalline planes. 



According to McConnell, single ice crystals are "per- 

 fectly brittle." However, since, in general, the fluidity 

 of a crystal depends on the temperature, some crystals be- 

 ing so fluid near the freezing point that their faces bulge 

 out or that their edges bend in a curve line under the action 

 of gravity {cf. Tammann, 1925, p. 291), it seems evident 

 that the individual ice crvstals should also show some 



