174 WET GROUND COMMUNITIES 
covered with sedges that we find marked differences in the ponds of 
different ages. 
b) Vegetation choked temporary pond association (Stations 41, 42, 43; 
Table XX XVII).—Sedges soon take possession of the bottom of such a 
pond as we have been discussing. Just how long a time is required is not 
known, though the pond which we are about to discuss is probably 
several hundred years old. Here we find nearly all the groups men- 
tioned as occurring in the younger ponds, but also certain ecological 
types which are characteristic of sedge-bottomed ponds. Most notable 
is the small green, flat, cigar-shaped worm (Vortex viridis) which usually 
occurs in numbers, and a small brown species of Mesostoma similar 
in form but brown in color. With them are often small larvae of 
dytiscid beetles (species unknown), caddis-worms (Phryganeidae) with 
cases made from pieces of grass (their relation to those in permanent 
ponds is not known), and the snail (Lymnaea modicella). 
As such a pond grows older the sedge becomes thicker and poses 
plants make their appearance. What is known as low prairie develops. 
At such a stage the small ponds like those we have been describing 
usually become partially filled and so never contain the best development 
of the older temporary pond community. We accordingly turn to the 
later history of the ponds discussed in the preceding chapters, which 
represent the best development of the temporary pond communities. 
In a forest climate when ponds are filled and drained they are 
occupied by forest. In the steppe climate they are occupied by steppe 
or prairie. In the forest border area, where our studies have been 
carried on, some ponds when filled are occupied by prairies, others by 
forest. Dr. Cowles is of the opinion that ponds with gently sloping 
sides and bottoms become covered with prairie, while those with steep 
slopes become covered with forest (Fig. 123). 
As ponds, such as we have discussed in the preceding chapter, 
become ecologically old, they dry in dry seasons. They usually become 
occupied by cattails, equisetum, or other grasslike plants. The red- 
winged blackbird (Fig. 124) occasionally nests in them. At such a 
stage the isopods (Asellus communis and Mancasellus danielst), amphi- 
pods (Eucrangonyx) (Fig. 113), and snails (Lymnaea reflexa) (Fig. 125; 
compare with Fig. 104, p. 149) arecommon. The fringe-legged mosquito 
(145) and the common marsh mosquito (Fig. 126) breed in such situations 
while the crayfishes and various of the old-pond species continue. 
When such a stage is reached, it is only a step to the typical tempo- 
rary pond. If the ground-water level is lowered, as is the case in many 
