CHAPTER XI 



PLANT SOCIETIES: ECOLOGICAL FACTORS 



123. Definition of plant society. — Fkiiii tlie previous 

 chapters it has been learned that every complex plant is 

 a combination of organs, and that each organ is related in 

 some special way to its environment. It follows, therefore, 

 that the whole plant, made np of organs, holds a very com- 

 plex relation with its environment. The stem demands 

 certain things, the root other things, and the leaves still 

 others. To satisfy all i_if these demands, so far as possible, 

 the whole plant is delicately adjusted. 



The earth's surface presents very diverse conditions in ref- 

 erence to plant life, and as jilants are grouped according to 

 these conditions, this leads to definite associations of plants, 

 those adapted to the same general conditions being apt to 

 live together. Such an association of plants living together 

 in similar conditions is a ijlanf sociefi/, the conditions for- 

 bidding other plants. It must not be understood that all 

 plants affecting the same conditions will be found living 

 together. For example, a meadow of a certain type will not 

 contain all the kinds of grasses associated with that type. 

 Certain grasses will be found in one meadow, and other 

 grasses will be foitnd in other meadows of the same type. 



Very closely related plants generally do not live in the 



same societv. as their rivalry is apt to be intense. Closely 



related pilants are likely to occttr, however, in ditferent 



societies of the same type. A plant society, therefore, ]nay 



contain a wide representation of the plant kingdom, from 



plants of low rank to those of higli rank. 



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