CAUSES OF THE PROGRESSIVE DEVELOPMENT OF VARIETIES. 83 1 



designedly, in which some character useful to man was more strongly manifested 

 than in the others ; those individuals were selected which best answered to a definite 

 requirement ; they alone were further cultivated ; the particular character was again 

 strongly displayed in some of their descendants, and only these individuals were 

 again selected for reproduction ; and the desired character was thus continually in- 

 creased in strength. Other characters of the plant also varied at the same time, but 

 they were disregarded, and the individuals in which they occurred were not preserved 

 for reproduction, and no increase of these characters consequently took place from 

 generation to generation. 



The greatest service which Darwin has rendered to science is to have shown 

 that wild plants are also subject to vital conditions the effect of which consists in 

 this, that only some of the varieties of one primitive form maintain themselves and 

 increase their peculiarities, while others perish. The relationship of the varying wild 

 plant to its environment in the broadest sense of the word is however different from 

 that of the cultivated plant to man ; man protects his charges in order to preserve 

 them ; he places them under favourable conditions in order that those properties 

 which are useful to him may become freely developed. Wild plants, on the contrary, 

 have to protect themselves against all injury from without ; their existence is con- 

 tinually threatened by other plants or animals or by the hostility of the elements ; 

 and in this Struggle for Existence^ as Darwin has appropriately termed it, only those 

 individuals are able to maintain themselves which are best able to resist the prejudicial 

 influences to which they are exposed; and only those varieties which happen to be 

 the best endowed in these respects will reproduce themselves and further develope 

 their special properties. Hence the characters of wild plants, as far as they are not 

 of a purely morphological nature, always show a perfectly definite relationship to the 

 conditions in which they are placed ; the form and other characters of the organs 

 have essentially for their object to secure the existence of the plant under the local 

 conditions of its habitat ; varieties and species which are not endowed with qualities 

 to endure the struggle for existence perish. The struggle for existence acts there- 

 fore in a certain sense similarly to the selection of the breeder ; as the breeder de- 

 velopes only that which is suited to his own purposes, so in the struggle for existence 

 only those varieties survive and reproduce their kind which are better adapted, 

 through some property which they possess, to endure the struggle. Thus, finally, 

 through imperceptible variation, through the destruction of those characters which 

 are not beneficial, and through the further development of the useful ones — in one 

 word, through what may be termed metaphorically Natural Selection in the struggle 

 for existence, — forms are produced which are as well or even better adapted for the 

 purpose of self-preservation than cultivated plants are for the purposes of man. By 

 the undesigned reciprocal influences of plants and of their living and physical 

 environment, specialities of organisation finally arise which could scarcely be better 

 adapted for the preservation of the plant under its special local conditions, and which 

 give the impression of being the result of the greatest ingenuity and foresight. 



In order to understand clearly how the struggle for existence has caused the 

 existing wild forms of plants to be so admirably adapted to their specific vital con- 

 ditions, it must be borne in mind that all plants are continually varying to a very 

 slight extent, and that the variation affects all their organs and all their characters, 



