PDF - Wallace Online

468 TROPICAL NATUREour gardens, showing that peculiarities of soil and climate, arenot of vital importance ; but not one in a thousand of theseplants ever runs wild with us, or can be naturalised by themost assiduous trials ;and if we attempt to grow them undernatural conditions in our gardens, they very soon succumbunder the competition of the plants by which they are surrounded.It is only by constant attention, not so much tothem as to their neighbours by pruning and weeding closearound them so as to allow them to get a due proportion oflight, air, and moisture, that they can be got to live. Letany one bring home a square foot of turf from a common orhill-top, containing some choice plant growing and floweringluxuriantly, and place it in his garden, untouched, in themost favourable conditions of light and moisture, and in ayear or two it will almost certainly disappear, killed out bythe more vigorous growth of other plants. The constancy ofthis result, even with plants removed only a mile or two, is amost striking illustration of the preponderating influence oforganism on organism, that is, of the struggle for existence.The rare and delicate flower which we find in one field orhedgerow, while for miles around there is no trace of it,maintains itself there, not on account of any specialty of soilor aspect, or other physical conditions being directly favourableto itself, but because in that spot only there exists theexact combination of other plants and animals which alone isnot incompatible with its wellbeing, that combination perhapsbeing determined by local conditions or changes which manyyears ago allowed a particular set of 'plants and animals tomonopolise the soil and thus keep out intruders. Such considerationsteach us that the varying combinations of plantscharacteristic of almost every separate field or bank, or hillside,or wood throughout our land, is the result of a mostcomplex and delicate balance of organic forces the finaloutcome for the time being of the constant struggle of plantsand animals to maintain their existence.Geographical Distribution and Dispersal of OrganismsAnother valuable set of experiments and observations arethose bearing on the geographical distribution of animals andplants a branch of natural history which, under the old idea