44 BIG SPRING PRAIRIE. 
promises to hold out forsome years tocome. Itis also 
holding its own in a few other well drained areas. 
In the depressions of area Fof Map II, Typha lat- 
ifolia (Cattail} was very abundant before the last deep- 
ening of ditch, after which a gradual decrease in abund- 
ance occurred. Yet it was fairly common even in 1900, 
the year before the greater portion of this area was 
brought under cultivation. 
Isnardia palustris (Mud Purslane) and Proserpinaca 
palustris (Mermaid Weed) are other striking examples 
of plants yielding slowly to the changed condition. A 
specimen of Proserpinaca was found late in the Autumn 
on a pieceof ground which had been planted to pota- 
toes. It survived in spite of cultivation, but it had 
changed its general habit. Instead of growing long 
and slender, it formed a dense mat about eight inches 
in diameter, which closely hugged the ground. 
Salix myrtilloides and Betula pumila are frequent- 
ly found growing along the well drained banks of 
ditches three to five feet deep, although they are char- 
acteristic swamp plants. The evident explanation of 
this lagging of effects is found in the facts of well devel- 
oped root system of most of the plants cited in connec- 
tion with the great water content of the muck of this 
prairie. 
5. PLANT SOCIETIES OF THE PRAIRIE. 
Although there is only a moderate difference in the 
surface level of the prairie, yet there are quite distinct 
plant societies flourishing in close proximity to each 
other. Some times the difference in surface level is 
not more than one or two feet yet on the slightly higher 
portion, a mesophytic forest formation may have been 
developed, while a hydro-mesophytic prairie society 
may be firmly established on the slightly lower level. 
Again on another part of prairie considerably higher 
than the wooded portion, a prairie society may be hold- 
ing sway. Mere elevation can not reconcile these 
