OF PLANTS. 243 



knowledge, dependant, we quickly find that only a small 

 number of physical forces are as yet detected by us, in 

 their action on the organism, that on the other hand, a 

 proportionately large number at present altogether baffle 

 our endeavours after a more accurate comprehension of 

 their action, although we may safely assert that the life 

 of the plant is, and must be, as much dependant on them 

 as upon the others. Merely by way of example, I will 

 mention light, electricity, and the pressure of the atmo- 

 sphere. The two first, as continually in action in every 

 chemical process ; the last, of essential importance in all the 

 processes and relations between gases and vapours, must 

 likewise powerfully affect the life of the plant, which con- 

 sists in progressive chemical combinations and separations, 

 in continual absorption and excretion of vapours and gases. 

 The how is as yet a complete mystery to us, and many of 

 the at present wholly incomprehensible conditions in exten- 

 sion and distribution of species, may sooner or later find 

 sufficient explanation in these influences. 



If from the snow-covered ice-plains of the extreme 

 North, where the Red-snow Alga alone reminds us of the 

 existence of vegetable organization, we turn toward the 

 south, a girdle first expands before us, in which Mosses 

 and Lichens clothe the soil, and a peculiar vegetation of 

 low plants with subterranean, perennial stems, and generally 

 large, handsome flowers, the so-called Alpine plants, gives 

 a special character to Nature. Almost all the plants form 

 little flattened, separate tufts ; Pyrola, Andromeda, Pedi- 

 cularis, Cochlearia, Poppies, Crow-foots, and others, are 

 the characteristic genera of this Flora, in which no tree, 

 no shrub flourishes. Leaving this region, which Botanists 

 call the Region of Mosses and Saxifrages, or after one of 

 the founders of Geographical Botany, Wahlenberg's region, 



16* 



