1918] ROBBINS—BOULDER PARK 519 
conditions remain unchanged, the process of encroachment will be 
extremely slow. However, physiographic agencies are destroying 
the dry grassland habitat at a rate which exceeds that of biotic 
agencies. At many points the high terrace is being eroded by the 
stream, and invariably the flood plain temporarily culminates in 
meadow; again, débris is accumulating at the bases of slopes and 
in the depressions between glacial hammocks. On this fine grained 
and deeper soil, with its greater water retentiveness, meadow 
species become well established; hence it is seen that the combined 
activities of biotic and physiographic factors are resulting in the 
slow disappearance of the dry grassland and the establishment 
thereupon of a mesophytic grassland. FULLER (6) points out that 
whereas the hydrarch succession of Boulder Park is closely com- 
parable to that of the Illinois prairie, the Park area exhibits a 
xerarch succession comparable to nothing found in Illinois. 
Two types of meadow are displayed in the Park which we have 
designated “herbaceous meadow” and “meadow scrub.” The 
latter consistently occupies moister situations, and very frequently 
precedes herbaceous meadow in the succession. 
The seasonal aspects and detailed structure of the meadow need 
not be entered into extensively here. REED (21) has given us a 
report of the chief meadow societies in the Park, together with a 
list of the meadow plants with their frequency and soil moisture 
index. 
Carex festiva forms distinct meadow societies on the middle 
terrace and about the lakes. Where the slope of the lake shore is 
gradual, sedge moor immediately joins on to this society. Its 
chief associates are Deschampsia caespitosa, Phleum alpinum, 
Potentilla gracilis Dougl., Poa Buckleyana Nash, and Poa pratensis 
A conspicuous society of Pedicularis Parryi Gray occurs just 
outside the Carex festiva society in soil that is drier and more shal- 
low. A quadrat census of the plants of the society showed the 
Principal species to be Potentilla gracilis, Astragalus alpinus L., 
Pseudocymopterus sylvaticus A. Nels., and Chondrophylla F remontit 
(Torr.) A. Nels. The most unobservant person would remark 
about the well defined limits of the Pentstemon procerus Dougl. 
society. It extends in a semicircle about the south flank of a low, 
