MICHIGAN ACADEMY OF SCIENCE. 
53 
List of the Species of the Scirpus validus Association. 
DOMINANT SPECIES. 
Heir pus validus. 
SECONDARY SPECIES. 
Myriophyllum spicatum . Elodea canadensis. 
Cham spp. 
RELIC SPECIES. 
JSfi/inphaea amcricana (sparingly). Scirpus americanus (in reversal of 
successions caused by higher 
water) . 
INVADING SPECIES. 
Scirp 1 1 s a in ericanu s . 
(The following are of very local occurrence as noted above.) 
Decodon verticillatus. 
Eupatorium perfoliatum. 
Eu pat o> 'iu, m pu rpureu in. 
Lobelia cardina lis. 
Asclepias incarnata. 
Salix ludda. 
Sa gift aria latifo li a. 
Glyceria borealis. 
The Scirpus americanus Association. 
Extending from shallow water up on to the beach occurs the associa- 
tion dominated by the rush Scirpus americanus. It is fairly well repre- 
sented in the protected bays of Douglas Lake. On the lakeward side 
it is usually bordered by either Eleocharis palustris vigens or Scirpus 
validus , but occasionally by open water. Landwards it extends up out 
of the water as far as the sand is moist clear to the surface. Relic 
plants, whose stems are very often spirally twisted, may persist for a 
while higher up on the beach. Scirpus americanus does not have a very 
wide range of water depth, as the season of 1911 shows. The heavy 
rains of the spring raised the level of the lake about two feet. The 
dry spell commenced in June but the water had not receded to its 
natural level until long in August. Many of the patches of Scirpus 
americanus were killed. The dead plants turned jet black and were 
probably suffocated on account of lack of air. The depth of water 
over these killed patches was not more than eight inches during August 
but only very rarely was there sufficient life left to send up a stalk, 
altho further in towards the land there was the normal growth of this 
plant. Scirpus validus began to come in rapidly and by the end of 
August had recaptured a few of the Scirpus americanus areas. 
On the landward side, evidences of a true genetic succession are not. 
conspicuous. The edaphic conditions are changed rather suddenly as 
is also the change in the plant life. Very frequently there is an open 
strip of sand between the Scirpus americanus and the land vegetation. 
On the low, level, sandy spits, where the slope is hardly perceptible, 
evidences of the relationship of the land and water associations appear. 
As a rule it is the Potent ill a anserina association that comes into the 
