Tg18] ROBBINS—BOULDER PARK 513 
important aquatic in the filling process. Potamogeton foliosus Rai., 
P. lonchites Ruck., P. alpinus Balb., P. interior Rydb., P. lucens L., 
and Myriophyllum spicatum L. are other rather rare aquatics to be 
found here. 
Aquatic plants play an important part in the life history of the 
lake. On the flat, mud shores the S parganium association is 
Fic, 11.—West shore at Park Lake; note Sparganium in shallow water, and zones 
of sedge moor and willow thicket. 
immediately succeeded by the Eleocharis-Ranunculus community. 
This is well shown at the southwest shore (fig. 12). This shore is flat 
and gravelly or muddy, with a few small boulders scattered about. 
It is perennially covered with an inch or so of water up to about 
July 1, after which time it is a mud and gravel flat. Dwarf forms 
of Sparganium angustifolium flourish in this habitat. Eleocharis 
.acicularis here, as elsewhere in such habitats, is the chief invader 
of the bare soil. Following close behind and upon pure tufts of 
Eleocharis come Allocarya scopulorum and Alopecurus fulvus, in the 
