26 
ADAPTATION 
same time it must be clearly recognized that while on the 
whole disadvantageous characters tend to disappear, there 
are probably great numbers of them in existence ; the plants 
which possess them may overbalance them with advantageous 
characters, or may be slowly dying out in consequence of 
them. A plant or species will win or lose in the struggle 
for existence on the total of all its characters. Correlation 
may possibly produce disadvantageous characters at the 
same time as advantageous, or a given cause acting on 
different organs of the plant may possibly produce advan- 
tageous variations in some, disadvantageous in others. 
It is very difficult to decide which if any of the characters 
of a plant or species are adaptations to its mode of life. A 
species may possess some character admirably suiting it for 
one mode of life, though acquired for some other, and if it 
be found living in the former mode we shall be liable to 
mistake this character for an adaptation to that mode of 
life. Examples of this are given in Chap. III. under 
Epiphytism. Or again, a species may possess some cha- 
racter of little or no importance in its mode of life but which 
may prove of great importance in some other environment, 
should it happen to be placed there. 
The study of adaptation is carried on by the comparison 
of all forms living in similar surroundings, e.g. all water- 
plants, or all parasites, &c. The members of these eco- 
logical groups of plants belong usually to many distinct 
families and their retained ancestral characters therefore 
differ ; if now we find among such a group certain characters 
in common, which are hereditary and are useful in the 
particular mode of life characteristic of the group, we may 
feel pretty sure that we are dealing with genuine adaptations. 
In such comparative study too, it is brought out in a very 
striking manner that the same end is attained in a great 
variety of ways, e.g. different organs in different species 
may be modified in their descendants in such a way as to 
resemble one another in structure and function. Good ex- 
amples of this may be found among xerophytes (Chap. III.), 
e.g. by comparing the various ways in which storage of water, 
or reduction of the transpiring surface, is effected. 
The science of ecology has to deal with all the characters 
of a plant, structural and functional, in relation to the 
