468 TROPICAL NATURE Ix 
our gardens, showing that peculiarities of soil and climate are 
not of vital importance; but not one in a thousand of these 
plants ever runs wild with us, or can be naturalised by the 
most assiduous trials; and if we attempt to grow them under 
natural conditions in our gardens, they very soon succumb 
under the competition of the plants by which they are sur- 
rounded. It is only by constant attention, not so much to 
them as to their neighbours—by pruning and weeding close 
around them so as to allow them to get a due proportion of 
light, air, and moisture, that they can be got to live. Let 
any one bring home a square foot of turf from a common or 
hill-top, containing some choice plant growing and flowering 
luxuriantly, and place it in his garden, untouched, in the 
most favourable conditions of light and moisture, and in a 
year or two it will almost certainly disappear, killed out by 
the more vigorous growth of other plants. The constancy of 
this result, even with plants removed only a mile or two, is a 
most striking illustration of the preponderating influence of 
organism on organism, that is, of the struggle for existence. 
The rare and delicate flower which we find in one field or 
hedgerow, while for miles around there is no trace of it, 
maintains itself there, not on account of any specialty of soil 
or aspect, or other physical conditions being directly favour- 
able to itself, but because in that spot only there exists the 
exact combination of other plants and animals which alone. is 
not incompatible with its wellbeing, that combination perhaps 
being determined by local conditions or changes which many 
years ago allowed a particular set of plants and animals to 
monopolise the soil and thus keep out intruders. Such con- 
siderations teach us that the varying combinations of plants 
characteristic of almost every separate field or bank, or hill- 
side, or wood throughout our land, is the result of a most 
complex and delicate balance of organic forces—the final 
outcome for the time being of the constant struggle of plants _ 
and animals to maintain their existence. 
Geographical Distribution and Dispersal of Organisms 
Another valuable set of experiments and observations are 
those bearing on the geographical distribution of animals and 
plants—a branch of natural history which, under the old idea 
