142 POND COMMUNITIES 
will grow for a long time, so the bottom becomes a humus- and chara- 
covered bottom. 
3. THE SUBMERGED VEGETATION ASSOCIATION 
(Ponds 1, 5, and 7; Stations 32, 33, and 34) 
The Chara community is entirely different from that of the bare 
bottom, and differs also from that of other vegetations. Chara is highly 
siliceous. It is probably eaten only accidentally by animals or at least 
forms no important part of their food. It should be considered simply as 
a covering for the bottom and a resting- and living-place for animals. 
Some fish culturists (113) have said that it is very rich in life. This 
may be true under certain artificial pond conditions; but the chara 
ponds are poorer than any others of our series. Chara differs from some 
other plants in not reaching to the surface of the water. Many aquatic 
insects that carry air beneath the surface must cling to objects which 
reach the surface when obtaining a fresh supply, and others must crawl 
to the surface on some object in order to emerge from the nymphal skin 
(96). Associated with chara are often growths of bulrushes near the 
sides of the ponds and on the sterile bottom. In the sparse chara the 
most characteristic animal forms are Anodonta grandis footiana (Fig. 86), 
and the musk turtle (Aromochelys odorata), which is abundant on these 
bottoms but is not found elsewhere. There are often nests of a few un- 
identified fishes that clear off the bottom in building. The burrowing 
dragon-fly nymph (Fig. 87) lives on the bottom among sparse chara, in 
the presence of but little oxygen. It lies half buried in the mud, with its 
abdomen protruding a little at the end. The mud minnow (Umbra limi) 
(Fig. 88), the golden shiner (Abramis crysoleucas) (Fig. 88), the chub- 
sucker (Erimyzon sucetta), bullheads, the little pickerel (Esox vermicula- 
ius), the tadpole cat (Schilbeodes gyrinus), and occasionally the warmouth 
bass (Chaenobryttus gulosus) spend their time in the denser chara. The 
shiner and mud minnow place their eggs on the chara or other plants. 
Among the most abundant forms in the association are the midge 
larvae (Chironomus); these (Figs. 89, 90, 91) are present sticking to the 
vegetation in their small silken cases in great numbers (81). They are 
important articles in the food of the fishes. Aquatic insects are not 
numerous except for the midge larvae and a little May-fly. Others 
are occasional horseflies (Fig. 92), damsel-fly nymphs, May-fly nymphs 
(Siphlurus sp.), and occasional dragon-fly nymphs (Tramea, Anax, 
Leucorhinia). There are also a number of dytiscid beetles, many of 
which are common in all shallow waters, even rain pools, because of 
their powers of flight. 
