PLANTS OF WESTERN LAKE ERIE. 
69 
demerswn , Lemna trisulca , L. minor , L. polyrhiza , and Wdlffia Columbiana are free- 
swimming forms, either submersed or floating. With them are associated masses 
of ALesocarpus , Spirogyra , Ilydrodictyon , and frequently quantities of Osdllarid , 
Lyngbya , and other related forms. 
Microscopic algge, especially Desmidece and Diatomaceai , occur in great numbers 
upon the larger plants in quiet water. They are especially numerous in the silt and 
dirt that collect upon narrow-leaved plants, as Utricularia vulgaris and Bidens beckii, 
but they are infrequent on Oeratophyllum , even when this grows near plants of 
Utricularia well supplied with microscopic life. 
The plants of the third group occupy by far the largest place in aquatic 
vegetation. Though not always as conspicuous 
as the plants with floating leaves, they cover a 
much greater area and make up the mass of 
the vegetation. The Characeos combine with 
Naias and Elodea to cover the bottom in water 
up to 10 or 12 feet in depth. Ileteranthera 
graminea , Vallisneria spiralis , Bidens bechii , 
species of Myriophyllum , Ranunculus , and Potamogeton grow to near the surface 
of the water, and in favorable locations make a dense growth. Bidens bechii also 
has aerial leaves. In this group must be included the attached submersed algae, 
as Chcetophora , Clddophora , species of 
CEdogonvum and the like. 
The Potamogetons and Nymjdnm- 
cece of the fourth group are nearly all 
vigorous plants and form the most con- 
spicuous feature of aquatic vegetation. 
In our waters the plants of this group 
are Nymplum tuberosci , Nupliar advma, 
NelvmMwnluteum , Polygonum muhlen- 
bergii , and several species of Potamo- 
geton. Nelumhium lutewm has both 
floating and emersed leaves. The root- 
stocks of the Nyrn phcmcece are thick 
and stout, while those of the Potamo- 
getons are slender. The floating leaves 
are always thick and leathery. 
To the swamp-plant group belong 
all of the species rooting in the mud 
and not truly aquatic, including such 
forms as Sagittaria , Typha, Spargan- 
iwn, Alisma , Acorns , Dianthera , many 
Gyperacece , and some grasses. These 
all root in the mud in shallow water 
and have nearly their entire vegetative system exposed to the air. They are 
generally characterized by slender stems and long, narrow leaves. In Sagittaria , 
Sparganiurn , and Typha the lower portion of the stem is usually thick and spongy; 
Fig. D . — Potamogeton lonchites, section through a bundle. 
Fig. C . — Potamogeton lonchites, section through a 
portion of submersed leaf. 
