ST. VINCENT, CAPE VERDE ISLANDS. 45 



In the Green Mountain, the appearance of the several plants 

 at successive heights is due mainly to the gradual increase in 

 amount of moisture received by the soil as a higher and higher 

 zone is reached. Closely similar conditions determine the distri- 

 bution of plants on many other mountains, such as on Green 

 Mountain in the Island of Ascension. 



The distribution of plants in successive zones on mountains 

 which is most familiar, is that brought about by a successive 

 decrease in temperature with increase of altitude, the Alpine flora 

 being that which withstands a prolonged covering of snow. In 

 Kerguelen's Land thus, a rapid decrease of vegetation is en- 

 countered as the mountains are ascended, and at 1,000 feet 

 most of it ceases. 



On some active volcanoes, however, as at the Banda Group near 

 the Moluccas, a gradual decrease in the vegetation in correspon- 

 dence with increased altitude is brought about by exactly opposite 

 conditions, namely, gradual increase of heat. Here, close to the 

 crater at the summit, the soil is excessively hot, yet one or two 

 plants grow in it where it is almost too hot for the botanist's 

 hand, and these straggle upwards, beyond distanced more sensi- 

 tive competitors, till a region is reached which is barren of all but 

 lowly organized algse, which grow around the mouths of natural 

 steam jets, as about the hot springs in the Azores and elsewhere. 



In very high latitudes only, apparently, is the vegetation 

 not influenced by altitude. On the mountains in East Green- 

 land, the same plants extend from sea level up to as high 

 as 7,000 feet altitude. This circumstance is accounted for by 

 the fact that here the sun never rising far above the horizon, its 

 rays strike the mountain-slopes nearly or quite vertically, and 

 hence by their greater power compensate for the larger amount 

 of heat lost by radiation at great elevations. The flat land 

 receives the rays on the other hand very obliquely, and hence 

 with much less force.* 



The combination of effects due to difference of aspect with 

 regard to the trade wind and sun produces a marked difference 



* "Die Zweite Deutsche Nordpolarfahrt in den Jahren 1869 und 

 1870," 2ter Bd. Wissenschaftliche Ergebnisse. Leipzig, F. A. Brockkaus. 

 " Klima und Pflanzenleben auf Ostgronland," von Adolph Pansch in Kiel. 



