CAUSES OF THE PROGRESSIVE DEVELOPMENT OF VARIETIES, gig 



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 conditions of life 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 by means of 

 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 pur- 

 poses of man. By the undesigned reciprocal influences of plants and of their living 

 and physical environments, 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. 



On the other hand, certain specialities of organisation which are essential in the 



struggle for existence may disappear in consequence of continued cultivation. 



[ildebrand points out^ that Peas, Beans, Lentils, Cereals, Buckwheat, all develope 

 under cultivation large heavy seeds which cannot be self-sown, so that these plants 



?hen left to themselves do not become wild, but disappear in consequence of having 

 ^lost the specialities of organisation which effect the dispersion of their seeds and 

 which protect them from animals. The same is the case with cultivated plants the 



fruits of which have been modified for the use of man, and have become useless in 



Hildebrand, Die Verbreitungsmittel der Pflanzen, Leipzig 1873. 

 30 



