MESOPHYTE SOCIETIES 215 
These new societies have been formed by the introduction 
of weeds and culture plants. 
146. The two groups of societies, Two very prominent 
types of societies are included here under the mesophytes, 
although they are probably as distinct from one another as 
are the mesophyte and xerophyte societies. One group is 
composed of low vegetation, notably the common grasses 
and herbs ; the other is a higher woody vegetation, composed 
of shrubs and trees. The most characteristic types under 
each one of these divisions are noted as follows. 
Among the mesophyte grass and herb societies are the 
" arctic and alpine carpets," so characteristic of high lati- 
tudes and altitudes where the conditions forbid trees, shrubs, 
or even tall herbs ; " meadows," areas dominated by grasses, 
the prairies being the greatest meadows, where grasses and 
flowering herbs are richly displayed ; " pastures," drier and 
more open than meadows. 
Among the woody mesophyte societies are the " thick- 
ets," composed of willow, alder, birch, hazel, etc., either 
pure or forming a jungle of mixed shrubs, brambles, and 
tall herbs ; " deciduous forests," the glory of the temperate 
regions, rich in forms and foliage display, with annual fall 
of leaves, and exhibiting the remarkable and conspicuous 
phenomenon of autumnal coloration ; " rainy tropical for- 
ests," in the region of trade winds, heavy rainfalls, and 
great heat, where the world's vegetation reaches its climax, 
and where in a saturated atmosphere gigantic jungles are 
developed, composed of trees of various heights, shrubs of 
all sizes, tall and low herbs, all bound together in an inex- 
tricable tangle by great vines or lianas, and covered by a 
luxuriant growth of numerous epiphytes. (See Figs. 195, 
197, 198, 199.) 
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