IN DETAIL 207 
are consequently much less conspicuots than the facies. A close inspection 
of the societies formed by principal species shows that they are far from 
uniform. Since they usually fail to exhibit distinct parts, it becomes neces- 
sary to approach the question of their structure from a new standpoint. 
Such is afforded by aggregation, which yields the simplest group in vegeta- 
tion, i. e., that of parent and offspring. This is so exactly a family in the 
ordinary sense that there seems to be ample warrant for violating a canon of 
terminology by using the word for this group, in spite of its very different 
application in taxonomy. It has already been shown that aggregation fur- 
produces a grouping of families, which may properly be called’ a com- 
Fig. 78. Calthetum (Caltha leptosepala), a consocies of the alpine bog 
formation. 4 
munity. As they are used here, family and community become equally ap- 
plicable to the association of plants, animals, or man. Both families and 
communities occur regularly in each society of the formation, and they repre- 
sent its two structures. In some cases, all the families are grouped in com- 
munities, two. or more of which then form the society. Very frequently, 
however, families occur singly, without reference to a community, and the 
two then constitute independent parts of the same area. This is typically 
the case wherever gregarious species are present, since these are merely 
family groups produced by aggregation. 
