181 



terminal cell of the staminal hair of Tradescantia put to 

 freeze at -12°. Some 18 hours after thawino-, the chromo- 

 somes had reappeared and cellular division had pro- 

 gressed. The cell was apparently not killed. 



Lenoir (1931) describes, in the cells of the ovary and of 

 the nucelle of Frit ill aria imperialis, after freezing, swollen 

 chromosomes or spiremes and a disorganized linin network. 



According to Detmer (1886), chloroplasts are disaggre- 

 gated after freezing in the same way as when plants are 

 killed by heat or by acids. 



Several experiments on tissues described above under 

 ''Phase Separation" contain information on the subject 

 discussed here. 



SUMMARY 



1. The formation of crystalline nuclei in a liquid is gen- 

 erally assumed to be initiated by collisions of molecules in 

 some definite conditions of orientation. 2. Crystallization 

 of water is sometimes considered as a precipitation of tri- 

 hydrol dissolved in dihydrol. 3. There is some evidence 

 that the formation of ice is preceded by a colloidal state. 

 4. It has been suggested that liquid water possesses a 

 quasi-crystalline structure and that little molecular rear- 

 rangement is required for obtaining the crystalline state. 



5. The freezing point of culture media varies from 

 - 0.01° to about - 2.5°. 6. That of plant juices was found 

 to lie between -0.3° and -2.5° for most species. 7. That 

 of the blood of aquatic animals is, in general, about the 

 same as that of their medium. 8. The individual differ- 

 ences in the freezing point of blood can be as much as 0.3 

 degree (in birds). 9. The freezing point of eggs follows 

 a cycle, being nearly the same as that of the mother's blood 

 during the period of their formation, then decreasing con- 

 siderably and rising again during embryonic development. 

 10. Living protoplasm (myxomycetes) was found to freeze 

 at the relatively high temperature of -0.17°. 11. Animal 

 and plant tissues congeal at temperatures extending from 

 about - 0.4° to - 3°. 12. The freezing point of living tis- 



