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 i, 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- 

 lus), 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. 



