MICHIGAN ACADEMY OF SCIENCE. 
51 
shallower water than that in which the Potaniogetons occurred. With 
them it maintains a sharp tension line. Secondary species are seldom 
present in this region. 
This is a pioneer association in the open water in some of the creeks 
of the region, but where it is competing with other associations, it 
normally follows the C as t alia A ymp ha e a association. It may give place 
to any one of several associations. In creeks, the Eleocharis association 
is more often the succeeding one but near the mouth of Bessey Creek 
it gives place to Scirpus validus. This occurs only on the side towards 
the shore, as the Alenyanthes-Sagittaria association can not exist in 
water subject to wave action. Sagittaria can not grow in water as deep 
as Scirpus validus is able to, yet when these two come into competition 
on ground that does not preclude the Sagittaria, it occupies a lower 
position in the genetic scale than Scirpus validus. In treeless bogs this 
association is succeeded by Carex filiformis or by Chainaedaphne caly- 
culata. One instance of succession to Phragmites-Typha was observed 
in a bog southeast of Douglas Lake. When occurring along the creeks 
in cedar bogs, it is usually separated from the Thuja by the Iris asso- 
ciation. 
List of the Species of the Menyanthes-Sagittaria Association : 
DOMINANT SPECIES. 
8a gift aria lati folia. Memyanthes trifoliate. 
Spargani urn simplex. 
SECONDARY SPECIES. 
Mentha arvcnsis canadensis. Mimuhis glahratus jamesii. 
RELIC SPECIES. 
Cast alia odorata. 
INVADING SPECIES. 
Eleocharis palustris vigens. Scirpus validus. 
Carex filiformis. Chainaedaphne calyeulat a . 
Typlia latifolia. Iris versicolor. 
The Eleocharis Association. 
In some of the sheltered bays where the slope of the bottom was very 
gentle this association of water plants was occasionally present. The 
water there was less than a foot in depth and the association extended 
out of water. The dominant species was Eleocharis palustris' vigens, 
a plant which spreads very rapidly by underground rootstocks and takes 
nearly complete control of the ground once it obtains a start. The 
secondary species were not numerous and only occasionally conspicuous. 
As a rule, this association seemed to be the end of Ibis genetic series, 
for between it and the land plants there was usually an open stretch 
of water in addition to the lower beach which was usually plantless. 
In a few of the long spits which project out into the waters of North 
Fishtail Bay succession to the Scirpus americanus association was clear- 
