CHAPTER XI 
PLANT SOCIETIES : ECOLOGICAL FACTORS 
123. Definition of plant society, From the 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 up 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 of 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 plants 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 plant society, 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 found in other meadows of the same type. 
Very closely related plants generally do not live in the 
same society, as their rivalry is apt to be intense. Closely 
related plants are likely to occur, however, in different 
societies of the same type. A plant society, therefore, may 
contain a wide representation of the plant kingdom, from 
plants of low rank to those of high rank. 
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