Chap. II] HEAT 41 



terrestrial vegetation in the antarctic polar zones is not due to an 

 absolutely greater cold there — for the thermometer does not fall so low 

 as in the north polar zones — but to the fact that the temperature 

 remains low, and almost constantly under the minimum of the essential 

 functions. 



Kjellman was impressed with the fact that contrivances which might be 

 considered as protective against cold are wanting in many arctic plants, for 

 instance in the above-mentioned Cochlearia fenestrata. Indeed, it appeared 

 to him that polar vegetation is externally no better protected against cold 

 than that of temperate zones. We may expand this statement and say : 

 Our present poivers of investigation do not enable us to recognize in plants 

 any special protective means against cold. The capacity of withstanding 

 intense cold is a specific property of the protoplasm of certain plants, and 

 is quite unassisted by protective means that are external, that is to say, 

 outside the micellae of the protoplasm. In Central Europe the absence of 

 external protective means against the cold may also be demonstrated ; 

 it is sufficient to look at any meadow or field during a frost. There we 

 can find such delicate plants as Bellis perennis, Stellaria media, and the 

 like, frozen hard and brittle as glass. These plants are exposed, quite naked 

 as it were, to the inclemency of the weather, and not protected against 

 the attacks of frost by any hairy tomentum, by any corky integument, 

 not even by a thick cuticle. When the thaw comes, the plants continue 

 to grow undisturbed. They are quite hardy in relation to any degree of 

 cold that we experience. 



Yet protective means against cold have been ascribed to many woody 

 plants. Bud-scales, corky integuments, the thick cuticle of evergreen 

 leaves, were formerly described as such. But these are actually protective 

 means against drought, as has been shown in the preceding chapter. A cold 

 soil, and especially a frozen one, is, as we already know, physiologically 

 dry, so that any plant rooted in it requires protection against transpiration. 

 Shallow-rooted low herbaceous plants are subjected to approximately 

 the same fluctuations of temperature as the soil on which they grow, and 

 are therefore less exposed to danger from desiccation than are deeply 

 rooted tall woody plants ; they are therefore relatively unprotected. 



It has often been stated that fatty oil may, in certain cases, be considered as 

 a protection against cold. Hence the phenomenon, which will be discussed further 

 on, of the conversion during winter of starch into oil, is commoner in our northern 

 species of trees than in trees that are more sensitive to cold (A. Fischer). Seeds 

 swollen in water are stated to withstand low temperatures better when they are 

 rich in oil than when they are poor in oil. In such cases, however, we are dealing 

 with mere conjectures, which lack any experimental basis, and seem to be con- 

 tradicted by other phenomena. 



