280 BOTANICAL GAZETTE [OCTOBER 
and Salix are often the first woody types to appear on the exposed 
places of the floodplain and bluffs appears to be due to nothing 
beyond the fact that they were first on the ground. Judging from 
the shrubs, dispersal by wind may be more rapid than dispersal by 
animals, but it is certainly far less prevalent, as will be shown later. 
4. Epapxic.—Of all the local conditions, the societies sustain the 
most obvious relation to the amount of available moisture in the soil. 
It is this which in large measure gives the distinctive characters to 
the bluff societies as compared with those of the floodplain or the peat- 
forming group. The relation which tension lines bear to water 
supply takes on particular interest in case of the bayou peat-forming 
societies indicated in the map. There is a slope toward the center 
in which there occurs a pond-like bay. The main part of the sur 
face water discharged from the seepage springs along the cemetery 
‘bluff is carried to the southeast to a point near the fence, where it 
makes a good sized stream as it flows directly to the ponds. A similar 
discharge of surface water comes from several points along the elm- 
ash-maple zone. The map shows the general tendency of tension 
lines to arrange themselves concentrically about the bay; also 4 
tendency to arrange themselves parallel to the stream, and the com- 
plex pattern of the peat-forming societies is the resultant of these 
conflicting tendencies. : 
A chemical analysis was made of the soil water about the springs 
in the hope that peculiarities might be detected to account for the 
xerophytic adaptations noticed in the vegetation. The water was 
found to be neither acid nor alkaline. It contains sulfates, chlor- 
ids, and carbonates, with iron, calcium, and sodium, but not differ- 
ent from the usual spring water. The water, however, is cold a2 
keeps the swamp at a low temperature. There are five of the societies 
which stand in so definite a relation to soil types that they give fail 
reliable information as to the kind of soil merely by their occurrence. 
The black oak society may be taken to indicate dry sand or grave < 
the oak-hickory society, till or clay; the tamarack society, eee 
the elm-ash-maple society, wet soils; the maple-beech society, 
ness of soil. Such soil relations do not appear to be limite 
valley alone, but to hold true over a considerable area outside. 
5. Biotic racrors,—It is due to the interaction of one life form 
