SOCIETIES 197 



control over a portion of an association where, of course, the environ- 

 ment is already controlled by the true dominants. It is thus a 

 dominance within a dominance. ]\Iore often it is the aspect rather 

 than the environment as such that is controlled by the subdominant 

 species. The growth habits of the subdominants are ordinarily 

 different from those of the dominants. For example, in a forest, 

 where the dominant species are trees, the subdominant species are 

 shrubs, herbs, or cryptogamic plants, and in a prairie, where the 

 dominant species are grasses, the subdominants are herbs or low 

 shrubs. 



Three kinds of plant societies are ordinarily recognized. The first 

 of these includes what are called aspect societies. These represent 

 the commonest and most important type of society. They are 

 ordinarily composed of subdominant herbs and they become con- 

 spicuous only during a certain season of the year, usually when they 

 are in flower. Thus in a deciduous forest one may find in early 

 spring a spring beauty (Claytonia virginica) society or a blue-eyed 

 Mary (Collinsia verna) society, either of which may control the aspect 

 or appearance of a portion of the association very completely during 

 a few weeks while the flowers are in bloom. By midsummer this 

 same area may be occupied by a wood nettle {Laportea canadensis) 

 society. Likewise in a desert community there are frequent aspect 

 societies dominated by California Poppies or lupines or other annual 

 or perennial herbs which come into bloom during or immediately 

 following a rainy season. In a prairie association some of the 

 societies may completely mask the dominant grasses for a time. This 

 is especially true of some of the late summer and autumn societies 

 that are composed of subdominant, coarse herbs of the composite 

 family. 



The second kind of society that we may recognize is the layer 

 society. In a forest very definite layers in the vegetation are recog- 

 nizable. These are usually the tree layer, the shrub layer, the herb 

 layer, and the cryptogamic layer. Societies may occur in any of 

 these layers except the tree layer. Every aspect society, of course, 

 occurs in one or another of these layers and so might be called a layer 

 society. There are some societies, however, especially in the shrub 

 and cryptogamic layers, that are evident at all seasons and these 

 are best spoken of as layer societies. There is also in every associa- 

 tion a subterranean layer and this undoubtedly contains societies, 

 especially of bacteria, but it is not well enough known to merit 

 discussion. 



