1918] ROBBINS—BOULDER PARK 505 
of the curves there are gravelly, sandy, or muddy shores of deposi- 
tion. The future history of this lake is now largely concerned with 
the activities of plants. In the developing of this oxbow lake 
Callitriche palustris L. and Batrachium trichophyllum (Chaix.) 
Bossch. are the first representatives of pond life. The main stream 
throughout the Park is too swift to allow the growth of any vegeta- 
tion within it except algae, chiefly Draparnaldia acuta (Agardh) 
Kuetz. and Prasiola mexicana J. G. Agardh. These are attached 
to the rocks in the stream bed. They flourish only in swift running 
water. Batrachium trichophyllum and Callitriche have appeared 
in the still water back of the sand bar. Encroachment by the 
vegetation now starts in from all sides, and the area quickly comes 
to willow thicket. Carex wutriculata sometimes becomes inter- 
polated at the margin between willow thicket and open water. 
It is an important invader of these shallow oxbows. It is frequently 
succeeded by Carex variabilis, which is in turn followed by willow 
thicket. An oxbow that has had its connection with the main 
current severed usually passes through the same stages of succession 
found about lake shores. 
Oxbow 3 is a somewhat different type from the preceding. The 
lake is shallow and has a muddy bottom, over which numerous 
small rocks are scattered. The orignal rock and gravel stream bed 
is thus still visible. The lake is free from water during the latter 
part of the season. Alopecurus fulvus is dominant on the muddy 
bottom. Associates are Ranunculus reptans, Eleocharis acicularts, 
and Sparganium angustifolium Michx. Carex utriculata is rapidly 
invading the Alopecurus society. Mixed with Carex is Glyceria 
americana, Alopecurus fulous, and a great deal of moss. Moss often 
invades the Carex utriculata association, preparing a substratum 
upon which willow thicket may build more readily. 
Oxbow 5 is a small and shallow pond which undergoes periodic 
drying. There is a well developed Eleocharis-Ranunculus asso- 
Ciation on the sandy bottom. It is being invaded by Carex uiri- 
culata, after which comes willow thicket. 
Oxbow 6 exhibits a pond that is now almost filled with vegeta- 
tion. A very small area of open water still remains. The lake was 
narrow and filled in a manner normal to gravelly or muddy shores, 
