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PLANT ASSOCIATIONS : 25 
CHAPTERIV 
PLANT ASSOCIATIONS 
ANYONE who has observed plants at all carefully must have 
noticed that certain plants grow together; those found in- 
hedgerows are different from meadow plants, those on exposed 
moors from the sheltered valley flora. 
Those plants which grow together under aoe conditions 
of soil and climate ae a Plant Association ; for instance, 
river plants, those growing above a certain height, those of a 
beech-wood, or those of a bog, constitute in each case an 
association ; they are related to each other ecologically, 
although they may belong to quite different Orders. As a 
rule, such plants will resemble each other in the structure of 
their stem or leaf, in their vegetative organs generally, how- 
ever widely different the flowers may be. 
In a Plant Association it is usual to distinguish between— 
(a) The plants which peewee in the given area—e.9., 
Heather, Oak, Grasses ; 
(b) The ordists forms which may be siuaoline for 
dominance—e.g., Bilberry with Cotton-grass ; 
(c) The plants dependent on the dominant forms. 
A Plant Association will include a larger or smaller number 
of forms, according to the dominant form selected. Thus, 
supposing the vegetation of a heather moor is being described, 
the plants found in the area in which the heather is pre- 
dominant will be more numerous than one in which the 
cotton-grass is the dominant form selected. Or, supposing 
the beech is selected as the dominant form, then the associa- 
tion will be smaller than if the oak were the chief form of the 
area fixed on for investigation. 
As yet comparatively little systematic work of this kind 
has been done in England, so that it is difficult to get sufficient 
