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Show 24 DARWINISM CHAP. river sometimes rose 30 feet in eight hours, doing. immense d es t rue tw. n, an d the abunda· nce of the brbo-er c.a rmvora and laro-e reptiles on its banks, he goes on : " But. 1t was among theb flora that the principle of natura~ s~lect10n was m~st prominently displayed. In such a d1stnct-overr~m With rodents and escaped cattle, subject to floods that earned a'~ay whole islands of botany, and especially to droughts. that dned the lakes and almost the river itself-no ordmary plant nop ld live even on this rich and watered alluvial debris. The c u ' h . l only plants that escaped the .cattle wer~ sue as ~ere mt 1er poisonous, or thorny, or resmous, or mdestruct1 bly tough. Hence we had only a great development of so~anums, talas, acacias, euphorbia.s, and laurels.. ~he ?utt~r?up 1s replaced hy the little poisonous yellow oxahs with Its viviparous buds ; . the pa.ssion-flowers, asclepiads, bignonias, convolvuluses, and cl~mhirw lcrruminou. pln.nts escape both floods and cattle by cl rmbin~ the hitrhest trees and towering overhead in a flood of b b l uloom. The ground plants arc the portulacas, turncras, t_UI( cenothems, bitter and ephemeral, on the bare rock, and almost independent of any other moisture than tl~o heavy dew.·. The pontedcrias, alismas, and plantago, with . g~asses ancl sedges, derive protection from the deep and bnllrant pools ; and though at first sight tho 'monte' doubtless impresses the traveller as a scene of the wildest confusion and ruin, yet, on closer examination, we found it far more remarkable as n. manifestation of harmony and law, and a striking example of the marvellous power which plants, like animals, possess, of adapting themselves to the local peculiarities of their ha,bita.L, whether in the fertile shades of the luxuriant 'monte' or on the arid, parched-up plains of the treeless pampas." A curious example of the struggle between plants has been communicated to me by Mr. John Ennis, a resitlent in New Zealand. The English water-cress grows so luxurian tly in that country as to completely choke up the rivers, sometimes loading to disastrous floods, and necessitn,ting grea.t outlay to keep the stream open. But a natural remedy haii now been found in planting willows on the banks. Tho roots of these trees penetrate the bed of the stream in every direction, and the water-cress, unable to obtain the requisite amount of nourishment, gradually disappears. II THE STRUGGLE FOR EXISTENCE 25 Increase of Organisms in a Geometrical Ratio. The facts which have now been adduced, sufficiently prove that there is a continual competition, and struggle, and war going on in nature, and that each species of animal and plant affects many others in complex and often unexpected ways. We will now proceed to show the fundamental cau. e of this struggle, and to prove that it is ever acting over the whole field of nature, and that 110 single species of animal or plant can possibly escape from it. This results from the fa ct of tho rapid increase, in a geometrical ratio, of all the speciofi of animals and plants. In the lower orders this increase is especially rapid, a single fie ·h-fly (Musca carnaria) produciwr 20,000 larvre, and these growing so qnickly that they reach their full size in five days; hence the great Swedish naturali. t, Linnrous, asserted that a dead horse would be devoured by three of these flies as quickly as by a lion. Each of those larvre remains in the pupa state about five or six days, so that each parent fly may be increased ten thousand-fold in a fortnight. Supposing they went on increasing at this rate during only three months of summer, there would result one hundred millions of millions of millions for each fly at the commencement of summer,- a number greater probably than exists at any one time in the whole world. And this is only one species, while there are thousands of other species increa. ing also at an enormous rate ; so that, if they were unchecked, the whole atmosphere would be dense with flies, and all animal food and much of animal life would be destroyed by them. To prevent this tremendous increase there must be incessant war against these insect , by insectivorous birds and reptiles as well as by other insect., in the larva as well as in the perfect state, by the action of the clements in the form of rain, hail, or drought, and by other unknown causes; yet we ee nothing of this over-present wa,r, though by its means alone, perhaps, we arc saved from famine and pestilence. Let us now consider a Jess extreme and more familiar case. We possess a considerable num her of hircls which, like the redbreast, sparrow, the four common titmice, the thrush, and tho blackbird, stay with us all the year ronml. Those lay on an average 1:iix eggs, but, as several of them have |