PLANT FORMATIONS. 525 



of mixed formations are seen in the mixture of joepye-weed 

 and boneset in low ground. This would then be a joepye-weed- 

 boneset formation. Each of these, however, often grows sepa- 

 rately, and then would form pure formations. In the forest, 

 beech, birch, and maple are sometimes mixed, forming a beech- 

 birch-maple formation. Again, oaks, beech, maple, and hem- 

 lock may form an oak-beech-maple-hemlock formation, and 

 so on, which may vary in different patches of an area, even 

 where the general conditions are the same, and the name of 

 the formation would vary accordingly. Besides the dominant 

 species of a formation there are subordinate species which may 

 not be prominent enough to change its aspect, but at most only 

 modify it. 



999. Fades. The term jades is sometimes applied to each 

 of the dominant species in a formation. Where there is but one 

 dominant species there is a single facies; where there are several 

 dominant species in a formation each one is a facies. 



1000. Vegetation forms. Vegetation form refers to the special 

 ecological form which individual species of a formation take 

 under the conditions, without regard to the importance of the 

 species in the formation. One or several vegetation forms may 

 be dominant (these would constitute the facies of the formation), 

 while others are subordinate or even inconspicuous. 



1001. Layers. By layers is meant the different strata in a 

 formation or society. While these are present to some extent 

 in nearly all plant societies, they are more marked in the forest 

 societies. The forest trees because of their greater height form 

 a canopy which shades the interior. The tall trees constitute, 

 therefore, the upper layer. Large shrubs growing in the forest 

 would constitute a second layer, small shrubs a third layer, 

 herbaceous plants a fourth, mosses, lichens, etc., on the ground 

 a fifth, and so on. The layers may in some cases be even more 

 numerous. 



1002. Zones. Applied to vegetation this refers to lateral layers 

 so clearly shown where there is radial or lateral topographic 

 symmetry. 



