226 A NATURALIST ON THE "CHALLENGER 



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plants are found to range from sea level up to 3,000 feet, and 

 there is no real limit of altitude ; even at 7,000 feet elevation 

 a thick cushion of moss, several inches in length, was found by 

 the German North Polar Expedition covering the ground.* 



This remarkable condition in the Arctic regions is mainly 

 accounted for by Dr. Pansch, by the fact that, with the sun 

 always near the horizon in high latitudes, the hill-slopes re- 

 ceive its rays nearly vertically on their surfaces, and thus 

 receive more radiant heat, even than the flat land below them. 

 There is little cooling at night, the clouds and mist preventing 



radiation. 



In Kerguelen's Land, of course, in its low latitude, the 

 inclined surfaces do not profit so much by their inclination. 

 There, as in the high north, the mosses and lichens are the 

 highest plants in range. In the successive groups of islands, 

 Marion, Kerguelen, Heard, they come lower and lower down the 

 mountain-slopes, and in Possession Island, south of the Ant- 

 arctic Circle, the few flowering plants remaining below them 

 at Heard Island have disappeared, and they are left growing 

 alone. 



In all the southern islands the density of the phanerogamic 

 vegetation, the extent of development of the individual plants, 

 and the number of species present, decrease directly with the 

 height. The facts show how much more the constant absence 

 of warmth, and a continuous moderately low temperature, is 

 inimical to plant development, than is periodical cold of the 

 severest kind. 



The condition of the vegetation in various localities in East 

 Greenland depends more on the distance of these from the ice 

 barrier, than on their position more or less north or south. The 

 vegetation becomes more abundant as progress is made inland, 

 away from the ice-bound coast. Exactly the opposite seems to 

 hold in Kerguelen's Land, where the chief source of warmth., 

 though at the same time the constant cause of the equalization 



* " Die zweite Deutsche Nord-Polarfahrt in den Jahren 1869 und 

 187o." 2. Bd. Wissenschaftliche Ergebnisse, Leipzig. F. A. Brockhaus. 

 " Kliin:i und I'ilunzenleben auf Qstgronland," von Adolf Pansch in Kiel. 



