CHAPTER IX. THE RESPONSE OF THE PLANT 
TO ITS SURROUNDINGS 
I. ECOLOGICAL FACTORS 
Mareriau. — A number of small flowerpots filled with soils of as many 
different kinds as can be found in the neighborhood. 
308. Definition.— By ecology is meant the relation of 
plants to their surroundings, which may be considered under 
three general heads: their relations to inanimate nature, 
to other plants, and to animals. The subject has been 
touched upon repeatedly in the foregoing pages, and, in 
fact, it is impossible to treat of any branch of botany with- 
out some reference to it. All that was said about the ad- 
justment of leaves for light and moisture, and their adap- 
tations for protection and food storage, about the devices 
for pollination, and for fruit and seed dispersal, really 
belong to ecology. 
309. Symbiosis. — The relations of plants to animate 
nature are biological factors, and may act in two ways: 
(1) through the destruction of vegetation by hungry ani- 
mals and by parasitic and disease-producing organisms; 
and (2) by associations for mutual benefit, such as are 
described in section vit of chapter VII. Associations of 
this kind are included under the general term symbiosis, 
a word which means “ living together.” In its broadest 
sense symbiosis refers to any sort of dependence or intimate 
organic relation between different kinds of individuals, and 
so may include the climbing and parasitic habits; but it 
is usually restricted to cases where the relation is one of 
mutual benefit. It may exist either between plants of one 
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