. Foundations of botany. th an exceptionally small supply of nitrogen or they must get it from an unusual source. The peat mosses adopt the former alternative, while the sun dews (Fig. 238), the pitcher-plants (Fig. 237), and some other species adopt the latter and derive their nitrogen supply largely from insects which they catch, kill, and digest. 399. Arctic Vegetation. — The seed-plants of thearctic flora are mostly perennials, never the large bulk of the underground portionas compared with that of the part above ground, theyare adapted to a climate in which they must lie dormant
. Foundations of botany. th an exceptionally small supply of nitrogen or they must get it from an unusual source. The peat mosses adopt the former alternative, while the sun dews (Fig. 238), the pitcher-plants (Fig. 237), and some other species adopt the latter and derive their nitrogen supply largely from insects which they catch, kill, and digest. 399. Arctic Vegetation. — The seed-plants of thearctic flora are mostly perennials, never the large bulk of the underground portionas compared with that of the part above ground, theyare adapted to a climate in which they must lie dormant Fig. Moss 328 FOUNDATIONS OF BOTANY for not less than nine months of the year. The flowersare often showy and apj^ear very quickly after the briefsummer begins. Mosses and lichens are abundant, — thelatter of economical importance because they furnish aconsiderable part of the food of reindeer. 400. Mountain or Alpine Vegetation. — In a general waythe effect of ascending a mountain, so far as vegetation is. Fig. 232. — A Plant of Arctic Willow. (About natural size.) concerned, is like that of traveling into colder was long ago suggested, in regard to Mount Ararat,that on ascending it one traversed first an Armenian, thena South European, then a French, then a Scandinavian,and finally an arctic flora. Up to a certain height, whichvaries in different latitudes, the slopes of mountains arevery commonly forest-covered. The altitude up to whichtrees can grow (or as it is commonly called in this countrythe timber line ) is somewhat over twelve thousand feet BOTANICAL GEOGRAPHY 329 in the equatorial Andes and lessens in higher latitudes asone goes either way from the equator. In the WhiteMountains, for instance, the timber line only rises to aboutfour thousand five hundred feet. The seed-plants of alpineregions in all parts of the earth have a peculiar and charac-teristic appearance. It is easiest to show how such plantsdiffer from those of the same species
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