PDF - Wallace Online

TROPICAL NATUREregions of polar cold or desert aridity the variety of groupsand species regularlydiminishes ;more and more are unableto sustain the extreme climatal conditions, till at last we findonly a few specially organised forms which are able to maintaintheir existence. In the extreme north, pine or birchtrees in the desert, a few palms and prickly shrubs or aromaticherbs alone survive. In the equable equatorial zonethere is no such struggle againstclimate. Every form ofvegetation has become alike adapted to its genial heat andample moisture, which has probably changed little eventhroughout geological periods and the never ceasing ;strugglefor existence between the various species in the same area hasresulted in a nice balance of organic forces, which gives theadvantage, now to one, now to another species, and preventsany one type of vegetation from monopolising territory tothe exclusion of the rest. The same general causes have ledto the filling up of every place in nature with some speciallyadapted form. Thus we find a forest of smaller trees adaptedto grow in the shade of greater trees. Thus we find everytree supporting numerous other forms of vegetation, and someso crowded with epiphytes of various kinds that their forksand horizontal branches are veritable gardens. Creepingferns and arums run up the smoothest trunks an immense;variety of climbers hang in tangled masses from the branchesand mount over the highest tree -tops. Orchids, bromelias,arums, and ferns grow from every boss and crevice, and coverthe fallen and decaying trunks with a graceful drapery.Even these parasites have their own parasitical growth, theirleaves often supporting an abundance of minute creepingmosses and hepaticae. But the uniformity of climate whichhas led to this rich luxuriance and endless variety of vegetationis also the cause of a monotony that in time becomes oppressive.To quote the words of Mr. Belt " : Unknown are theautumn tints, the bright browns and yellows of English woods ;much less the crimsons, purples, and yellows of Canada, wherethe dying foliage rivals, nay excels, the expiring dolphin insplendour. Unknown the cold sleep of winter ;unknown thelovely awakening of vegetation at the first gentle touch ofspring. A ceaseless round of ever-active life weaves thefairest scenery of the tropics into one monotonous whole, of