512 BOTANICAL GAZETTE [JUNE 
GLACIAL LAKE SUCCESSION 
The origin of Park and Filled Lakes, the only glacial basins in 
Boulder Park, has been discussed. It was pointed out that these 
two bodies occupy the positions of two ice cores that were left on 
the valley floor on the retreat of the first ice mass. Immediately 
following the melting of these ice cores there was left a cold water 
lake with bare gravel and stony shores. Park Lake was formerly 
of much greater size; the limits of the old shore may be clearly 
seen on the west side of the present body of water. This filled area 
is now in the sedge moor stage of development, as is also Filled 
Lake. We may gain some idea of the early stages in the develop- 
ment of the shore vegetation by studying the alpine lakes which 
- are found in abundance 6 or 8 miles west of Boulder Park. How- 
ever, this difference exists: alpine lakes are comparatively well 
protected by cirque walls from wind effects, whereas those of 
Boulder Park are in the open. It is believed that this difference _ 
explains the tardy development of forest growth in the Park, and 
the maintenance of the temporary climax grassland. 
In the lakes and ponds of Park Lake, algae are the only free 
floating plant life. Besides the numerous microscopic algae which 
constitute a portion of the plankton of these waters, Mougeotia 
laetevirens (A. Braun) Wittr. and Spirogyra Weberi Keutz. make 
up large floating masses along shores undisturbed by waves. 
Anabaena flos-aquae (Lyngbye) Breb. becomes conspicuous in late 
July when it appears as “water bloom” over the entire surface of 
the lake. 
Sparganium angustifolium Michx. (fig. 11) forms a well defined 
aquatic community along the shore edge out to a depth of about 
2 ft. It is of much importance in the aquatic successions. It 
grows equally well on a mud or gravelly bottom. A dwarf form 
occurs at the south of Park Lake on a low, flat area over which 
the water level fluctuates. Here the plants grow but a few 
inches high, and possess short, rather thick, leaves. Such plants 
mature fruit normally. Callitriche palustris L. is found in shallow 
water. It is most abundant where protected from wave action. 
Batrachium trichophyllum (Chaix) Bossch. is one of the first aquatics 
to secure a foothold in the ponds of the Park. It is the most 
