SUCCESSION OF COMMUNITIES I51 
present. With them are often found leeches, especially Macrobdella 
decora, which is a brilliant red-and-green form. The only character- 
istic insect is the dytiscid beetle (Agabus semipunctatus Kirby) (99c), 
a slender reddish-brown form. The other forms found here are inci- 
dental in the vegetation. Hollow logs are probably used for breeding- 
places by the fishes, such as the bullheads (105), while the eggs of Physa 
and of water-mites, and some of the aquatic insects, are also placed here. 
The mammals of these ponds are the muskrat, which occurs in all the 
stages, and the mink, which is now rare. 
Tendencies of the association: This association is unstable. Its 
fate is heralded by the incoming of different amphibious plants at the 
sides. This is the form Proserpinaca, with the divided leaves above 
water and the entire ones below. This is often associated with Equisetum 
and plants that have the growth form of grasses. Following these are 
the shrubs, such as the buttonbush (6). Before these have captured 
the entire pond it becomes dry during the dry season and the end of the 
aquatic community iscome. The formation which follows is the tempo- 
rary pond, swamp, or marsh type. 
Characters of the formation: The formation composed of the two 
associations mentioned may be characterized as made up of forms 
which require but little oxygen, and.no bare bottom. The reproduction 
is one of two types: either the young are carried or the eggs are attached 
to plants. Some of those carrying the young are the Sphaeridae, the 
amphipods, and the isopods. Those sticking the eggs onto or into the 
vegetation are the snails (all), the Dytiscidae, all the species recorded, the 
Hydrophilidae, the Notonectidae, the Belostomidae, the Ranatras, the 
caddis-flies, the Donacias, and in fact most of the forms of the formation. 
IV. SuccESSION 
The first formation to take possession of a pond when it is first 
separated from a lake like Lake Michigan is the bare-bottom formation; 
chara soon makes its appearance in the deeper parts and we have the 
beginning of the chara association. The chara association so acts upon 
the bottom by covering it with humus and vegetation that it renders 
the continued existence of the bare-bottom formation impossible (6, 
112, 114, 114a). At the same time it prepares a way for the vegetation 
which reaches to and above the surface. This, in turn, fills the pond 
still further, and the strictly marsh vegetation takes possession. The 
history of the true pond is then at an end and the story of the marsh 
begins. Our series of 95 ponds illustrates the series of stages. The 
