CAUSES OF THE PROGRESSIVE DEVELOPMENT OF VARIETIES. 929 
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. 
Hildebrand points out^ that Peas, Beans, Lentils, Cereals, Buckwheat, all develope 
under cultivation large heavy seeds which cannot be self-sown, so that these plants 
when left to themselves do not become wild, but disappear in consequence of having 
lost the speciahties 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. 
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