CHAPTER IX. THE RESPONSE OF THE PLANT 

 TO ITS SURROUNDINGS 



I. ECOLOGICAL FACTORS 



Material. — 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 viii 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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