282 GENERAL VIEWS,. 



They are succeeded by low herbs, furnished witii 

 leaves at the root, from the midst of which rises a short 

 stalk surmounted by small flowers. These pretty 

 plants take up their quarters in the clefts of rocks, 

 while the Grasses with their numerous slender leaves 

 spread themselves over the soil, which they cover as 

 with a rich verdant carpet. The Lichen, which feeds 

 the rein-deer, sometimes mixes in the turf: some- 

 times of itself covers vast tracts of country ; its white 

 tufts standing in clumps of various forms, looking like 

 hillocks of snow which the sun has not yet dissolved. 

 If we go farther, a naked land, sterile soil, rocks, and 

 eternal snows, are all we find. The last vestiges of ve- 

 getation are some pulverulent byssi, and some crustace- 

 ous Lichens, which cover the rocks in motley patches. 



The principal causes which induce this progression 

 of changes are three : 1st, the excess of duration in 

 the winters, a consequence of the obliquity and dis- 

 appearance of the solar rays ; 2d, the dryness of the 

 air, a consequence of the decrease of heat ; 3d, the 

 prolonged action of the light, which illumines the hori- 

 zon through the whole period of vegetation. I will 

 resume, in as few words as I can, the effects of each of 

 these three causes. 



It is well known that too great a degree of cold, by 

 eongealing the sap, occasions the rupture of the vascu- 

 lar system in plants, and thereby destroys them ; but 

 the deleterious action of cold is not confined to purely 

 mechanical results ; it has been proved that heat is a 

 stimulus that cannot be dispensed with in vegetation. 

 Many species secrete juices in warmer regions which 

 are unkhown in their economy in colder climates. The 

 Ash yields manna in Calabria, but loses that faculty as 

 it advances towards the nortfi. The grape m the soutb 



