147 



lion of water from the chromatin or from the cytoplasm 

 and an accumnhition of tliat water in the vacuoles. 



Lnyet and Gibbs (1937) made a detailed description of 

 the progress of freezing in the epidermal cells of onion. 

 After the congelation of the moisture present at the sur- 

 face of the mounted epidermis, some subcooled cells froze 

 suddenly, becoming opaque. Two separated phases could 

 then be seen in the frozen cells : ice and concentrated vacuo- 

 lar sap. The opacity decreased during the few seconds 

 subsequent to the sudden freezing, a phenomenon that the 

 authors attributed to a rapid growth of crystals. There 

 followed a slow transformation and growth of ice masses 

 (Fig. 26) which lasted for hours. 



Bugaevsky (1939), evidently unaware of the last-men- 

 tioned work, described the same process in epidermal and 

 subepidermal cells of the "underground part" of Avheat 

 plants. The ice crystals are said to grow within the proto- 

 plasm itself ; no mention is made of vacuoles. 



Buck (unpublished work; cf. abstract in Auaf. Rec, 72, 

 SuppL, 125, 1938) obtained the curious picture represented 

 in Figure 16 by freezing salivary gland chromosomes of 

 Ch'uouomus tentans. The nuclei, dissected out of the 

 gland and contained in a drop of water, were let fall into 

 a tube of petroleum ether cooled to about - 70°. The con- 

 tent of the tube was then evaporated in a high vacuum at 

 a temperature lower than - 30°. One of the nuclei so ob- 

 tained, photographed in fofo,i^ shown in the Figure. One 

 can distinguish several lobes of the coiled chromosomes. 

 The parallel lines seen across the nucleus seem to bear 

 no relation to the orientation of the chromosomes. The 

 author suggests that they represent regions of compressed 

 nuclear material, while the clearer stripes would represent 

 regions of reduced chromosomal content previously occu- 

 pied by ice (personal communication). 



C. THE FREEZING CURVES 



^[any experimental investigations on death or injury by 

 low temperature involve the study of freezing curves, that 



