CHAPTER IX 
THE ORGANIZATION OF PLANTS INTO SOCIETIES 
THERE are certain necessary things that all plants must 
have in order that they may grow. Some of these things 
are water, air, light, soil, and favorable temperature. All 
plants are not obliged to possess these in the same propor- 
tion, and some can live with one or two of these things 
very greatly in excess of the others, while other plants can 
endure quite unfavorable combinations of these factors. 
Plants are organized into societies in accordance with their 
relations to these different factors. It is not uncommon to 
classify these societies upon the basis of the water element. 
Thus in a general way there are usually recognized three 
groups: 
Hydrophytes, or water societies; xerophytes, or those in 
greatly exposed and dry regions; and mesophytes, those in 
conditions intermediate between those of the other groups. 
There may be some good objections to this basis of classifi- 
cation, since water can not always be said to be the deter- 
mining factor in a given environment. Within these groups 
may be recognized subdivision societies, as swamp society, 
rock society, etc. Furthermore, a society may take its name 
from its most conspicuous or most abundantly represented 
plant, as a beech, cactus, or water-lily society. 
Many plants try each year to get possession of a suit- 
able region in which to grow. Those especially favored by 
their adaptations in structure and habits will, to a greater 
or less extent, crowd out the others, and these must find 
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