95 



jurious to the poikilotlierms. 7. Tlic warm-blooded ani- 

 mals died at above-zero temperatures except if, as in the 

 case of hibernators, they had developed some adaptative 

 properties. 



GENERAL COMPENDIUM 



By their resistance to low temperatures, the plants and 

 animals considered in this review can be classified into 3 

 groups : 1. Those which can approach the absolute zero 

 without being killed; 2. Those which die near the freez- 

 ing temperatures ; 3. Those wdiicli die above the freezing 

 temperatures. 



The first group comprises : a) The forms wiiich support 

 desiccation, such as, the seeds, the spores (bacterial and 

 others), the protozoan cysts, the rotifers, the tardigrades. 

 the nematodes, b) A number of microorganisms of the 

 types, bacteria and yeast, some flagellates, some of the 

 lower fungi, and the infra-cellulars. All these resist 

 extreme temperatures without previous desiccation. 



The third group, namely that of organisms wdiich are 

 killed at above-zero temperatures, includes only the 

 homoiotherms and some of the higher plants. 



The large majority of plant and animal phyla belong, 

 then, to the second group, that is, to the kind of organisms 

 w^hich are killed at near-zero temperatures. There are, 

 it seems, two classes to be distinguished in this group: 

 1. The organisms which die Avhen their temperature is 

 lowered slightly below the freezing point. Usually these 

 organisms can support the formation of some ice in them 

 but they are killed wiien a larger proportion of their 

 w^ater-content solidifies. This has been observed in sev- 

 eral plant tissues, in some animal tissues and in entire 

 organisms, such as, the mollusks, the ami3hibia, the fishes, 

 etc. 2. The organisms wiiicli resist some 10, 20 or 30 de- 

 grees below freezing. Often a relatively large quantity 

 of ice can be formed in them, they become hard and break- 

 able, and they die, apparently wdien a last portion of their 

 cellular fluids solidifies. This is probably the case of 



