278 Eug. Warming. 



spots," we may also suppose with tolerable certainty, that 

 the ground on which they grew contained much water. Some 

 of the species, however, are not very particular in their 

 demands, since they are recorded as growing in "all loca- 

 lities," or "everywhere," as for instance, Cerastium alpinum 

 and Silène acaulis. The many varieties of the former perhaps 

 stand in direct causal connection with small differences in 

 the habitats. 



Transpiration. A factor which is connected with 

 what has been said above, and is of no less importance, 

 is the extent of the transpiration and of the atmospheric 

 humidity. 



Th. Wulff stated (1912, p. 5) that "the Arctic Flora 

 is of a decidedly xerophilous type." There are, it is true, 

 decidedly xerophilous types in the Arctic vegetation, which 

 I have probably been the first to record (1887) since I, in 

 chapter 5 (pp. 105- — 127), treated of "The Adaptations of 

 Heath-plants to Drought". It must, however, be remarked 

 that the woody plants of the heath and the rocky-flat 

 are what I especially treated, and amongst these one finds 

 in reality a number of distinctly xerophilous types. I pointed 

 out five different types of leaves, and even declared that 

 similar types are met with in the steppes and in deserts 

 — even in the Egyptian-Arabian desert, but I laid a great 

 stress upon the fact that this essentially applied only to the 

 woody plants of the heath. 



By far the greater majority of the species in question 

 are evergreens, this especially applies to the many woody 

 plants proper, the foliage-leaves of which remain for more 

 than one year. With regard to these one can speak of phy- 

 siological dryness, but hardly with regard to low-growing herbs. 



It is easy to understand that in woody plants the shoots 

 must become xerophytic in structure, — which is, as usual. 



