182 PLANT STUDIES 
132. Societies. Conspicuous among hydrophyte societies 
may be mentioned the following : (1) Free-swimming soci- 
eties, in which the plants are entirely sustained by water, 
and are free to move either by locomotion or by water cur- 
rents. Here belong the "plankton societies," consisting 
of minute plants and animals invisible to the naked eye, 
conspicuous among the plants being the diatoms ; also the 
"pond societies," composed of algae, duckweeds, etc., which 
float in stagnant or slow-moving waters. 
(2) Pondweed societies, in which the plants are an- 
chored, but their bodies are submerged or floating. Here 
belong the " rock societies," consisting of plants anchored 
to some firm support under water, the most conspicuous 
forms being the numerous fresh-water and marine algae, 
among which there are often elaborate systems of holdfasts 
and floats. The "loose-soil societies" are distinguished 
by imbedding their roots or root-like processes in the 
mucky soil of the bottom (Fig. 163). The water lilies with 
their broad floating leaves, the pondweeds or pickerel weeds 
with their narrow submerged leaves, are conspicuous illus- 
trations, associated with which are algae, mosses, water 
ferns, etc. 
(3) Swamp societies, in which the plants are rooted in 
water, or in soil rich in water, but the leaf-bearing stems 
rise above the surface. The conspicuous swamp societies 
are "reed swamps," characterized by bulrushes, cat-tails 
and reed-grasses (Figs. 164, 167), tall wand-like Monocoty- 
ledons, usually forming a fringe about the shallow margins 
of small lakes and ponds ; " swamp-moors," the ordinary 
swamps, marshes, bogs, etc., and dominated by coarse 
sedges and grasses (Fig. 163) ; " swamp-thickets," consist- 
ing of willows, alders, birches, etc. ; "sphagnum-moors," in 
which sphagnum moss predominates, and is accompanied by 
numerous peculiar orchids, heaths, carnivorous plants, etc. ; 
" swamp-forests," which are largely coniferous, tamarack 
(larch), pine, hemlock, etc., prevailing. 
