930 
ORIGIN OF SPECIES. 
the struggle for existence in the wild condition ; such are cucurbitaceous plants, 
fruit-trees, &c. Cultivation may so far affect edible fruits that they cease to develope 
seeds, as in the better kinds of Pears, in Grapes, Figs, Oranges, Dates, Bread-fruit, 
and Bananas ; thus the first and most important element in maintaining the struggle 
for existence, namely, reproduction by means of seeds, is destroyed. 
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 conditions 
of life, 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, 
although usually to an imperceptible amount. On the other hand, the struggle for 
existence in plants (as well as in animals) is a perpetual and never-ceasing one, in 
which the smallest advantage that the plant has obtained through variation in any 
one direction may be of the utmost importance for its perpetuation. 
The struggle which the plant carries on by means of its capacity for variation 
has two different aspects. On the one hand its tendency is to adapt its organisation 
completely to the conditions of food and growth afforded by the climate and the 
soil. It is evident that the organisation of a submerged water-plant must be different 
from that of a land-plant ; that the assimilating organs of a plant that grows in the 
deep shade of a wood must be differently constructed from those of a plant exposed 
daily to bright sunshine, and so forth. The conditions of life of all plants growing at 
a great elevation and in Arctic countries must be different from those growing in 
the lowlands of the Tropic and Temperate zones. If we had to do only with these 
general conditions of plant-life, the struggle for existence would be a comparatively 
simple process. It would be easy to imagine how, among the varieties of a primitive 
form which grew in water, there would be some which would be occasionally sub- 
jected to a subsidence of the water, and how these would give birth to descendants 
which would gradually assume the character of marsh- and finally of land-plants, 
as is well illustrated in the case of Nasturtium amphibiu?n, Polygonum amphibium^ 
&c.^ It may also be supposed that some of the descendants of a plant exhibit a 
somewhat greater power of resisting frost, that this property increases in the course 
of generations, and that thus a form which can at first only bear a temperate climate 
gradually produces varieties which can endure a more and more severe climate ; and 
so forth. Even these comparatively simple conditions would necessarily lead to a 
great diversity in the varieties descended from one ancestral form ; for each 
adaptation to new conditions of climate or locality would act in different ways ; 
i. e. varieties of different descriptions would take up and carry out in different 
ways the struggle against the influences of the elements. 
But the struggle for existence and the changes occasioned by it in the organ- 
isation of plants are greatly complicated by the fact that every plant, while struggling 
to adapt itself to its special conditions of life, has also to protect itself at the same time 
against a number of other plants and against the attacks of animals ; or, what is more 
to the point, its capacity for variation enables it to make use of particular favourable 
conditions which are offered to it by other plants and animals in order to take ad- 
^ A special interest attaches in this connection to Hildebrand's observation on Marsilia in Bot. 
Zeit. 1870, No. I, and Askenasy's on Ranunculus aquatilis and divaricatus in Bot. Zeit. 1870, p. 193 
et seq. 
