Caryophyllaceæ. 279 



exhibited in the anatomical structure of the leaves, — be- 

 cause they are higher in growth than are herbs, and often 

 may be without a snow-covering during the winter; their 

 leaves will frequently be exposed to the desiccating power 

 of cold and dry wind and this in a higher degree than those 

 of herbs, and the cold soil will for a long time prevent the 

 roots from absorbing water. The mnter, in particular, is a 

 very dry season of the year, and the higher the latitude, 

 the drier it becomes; but the danger of desiccation is much 

 less as regards the vegetative organs of herbs, because they 

 are generally lower in growth, and are, in addition, often 

 protected by the dwarf shrubs. 



If we now regard the leaves of the Caryophyllaceæ^ we 

 find no such adaptation for withstanding desiccation. On 

 the contrary, in the structure of their leaves they remind 

 one more of those of aquatic plants, or of herbs which grow 

 on damp, shady ground in woods. 



The epidermis has no specially thickened and cuti- 

 cularised outer walls. The stomata are situated very super- 

 ficially, occur often on both surfaces, and in great abun- 

 dance; the epidermal cells are most frequently highly un- 

 dulating; the mesophyll is very lacunose; aqueous tissue 

 does not occur; the epidermis is on the whole glabrous, and 

 in Cerastium alpinum alone a denser covering of hairs is 

 found; and hard bast occurs rarely and only in a few thicker 

 vascular bundles. These results agree, as already mentioned, 

 with those previously arrived at by several botanists, as 

 regards Arctic plants in general. 



The explanation is obvious: The rays of the sun 

 are very oblique; the lea\^es are but slightly warmed, al- 

 though the insolation may be very strong locally; the atmos- 

 pheric humidity is great (80 — 85%; see table in Borgesen); 

 fogs and cloud-covered sky are very frequent, also during 



