468 TROPICAL NATURE 



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 



