Lake Distriet: Interlacustrine Area. 397 
C es var, Michauxia combine with Naias flexilis and Elodea canadensis to cover the 
bottom in water up to IO or 12 feet in depth. Heteranthera graminea (= H. dubia), Vallisneria 
spiralis, es Beckii, Myriophyllum spicatum, Ranunculus (Batrachium) divaricatus and Potamo- 
geton pusillus, P. pectinatus grow to near the surface öf the water. In this association (Vallis- 
neria Association) must be included the attached submersed algae as Chaetophora, Clado- 
phora, Oedogonium. — A fourth association (Nymphaea Association) forms a conspicuous 
feature in Lake Erie vegetation consisting of een ee Nuphar (Nymphaes) advena, 
rss luteum, Polygonum Muhlenbergii, Potamogeton natans, P, pectinatus, P. pusillus, 
ii, P. lucens, P. amplifolius, together with Serie Sale and vr Typha, 
Phragmites in other places. 
A fifth association is formed by the strand-horizon, where f. e. in the neighborhood of 
eig Bog is found an assemblage z plants on as Fr = of the water-lily circumarea, 
It consists of Decodon (Nesaea) verticillatus, Pontederia co ‚ Sagittaria, Cephalanthus occi- 
ntalis, Alisma Paz, Lysimachia sah urgia) aller and Solanum Dulcam This 
circumarea is succeeded shoreward by öne consisting of non carolina, Cornus talonifes with 
Salix lucida, S. cordata, Lathyrus palustris, Scirpus americanus and other plants, which form a 
thicket that connects . aquatic formations with the forest on the higher ground. 
The numerous smaller lakes of the Interlacustrine Area are of glacial 
origin. They have been formed in three ways, (1) by the filling of a rocky 
basin; (2) by the formation of a dam of morainic material; (3) by the occu- 
pancy of a Kettle hole with water. Whatever their origin they show about 
the same stages of development until they finally disappear as lakes by being 
converted into sphagnum bogs by the encroachment of vegetation. The 
socalled Sister lakes in the Huron Valley in Michigan are of such a glacial 
origin. The largest of these lakes shows four fairly well defined vegetable 
horizons (or circumareas) occupying all the suitable lake bottom less than 
twenty feet under water ‘). Beginning with the innermost, they are: (1) a circum- 
area composed of Potamogeton zosteraefolius, which forms a dense tangled 
mat in water from eighteen to six feet in depth, with which is associated Fo- 
tamogeton lucens; (2) a circumarea of Nuphar advena between thirty and seventy 
feet in width. This plant which is associated with Pofamogeton natans, Chara 
coronata, Dulichium spathaceum and Typha latifolia grows as vigorously in 
water six feet deep as in water six inches deep. (3) A circumarea of Carer and 
Sphagnum, whose surface is practically at water level, extends landward from 
the water’s edge from six to twenty five feet. The most abundant phanero- 
gams are Carex filiformis and Potentilla palustris. (4) An circumarea of 
willows and poplars from ten to forty feet wide. The characteristic shrubs 
and trees are Salir alba var. vitellina, S. lucida, S. myrtilloides, Populus tre- 
muloides and Ulmus americana. 
wamp Formation. This formation is typically represented at Cedar Point, 
Sandusky Bay. Here the tall reed vegetation passes into a wet swamp asso- 
ciation where grow together in mixture Calamagrostis canadensis, carices (C. 
Schweinitzii, stenolepis, stipata, laxiflora, comosa, lanuginosa, tribuloides, lupu- 
lina, vulpinoidea), Lobelia syphilitica, Penthorum sedoides, Lathyrus palustris, 
ı)-RErp, Howarnp S.: A Survey of the Huron River Valley. Botanical Gazette XXXIV: 
125—139. August 1902. 
