Lake Distriet: Interlacustrine Area. 399 
Above the middle beach there is-a \. #trip characterized by the dominance of Elymus cana- 
densis, then a strip of Geranium Robertianum, then a strip of Artemisia canadensis, and finally 
one of Cornus stolonifera scattered in io strips are Prunus pumila, Oenothera biennis, Lathyrus 
maritimus, Carduus Pitcheri, Agropyron dasystachyum, Populus balsamifera, Tanacetum huronense, 
nemone multi 
The strand along Lake of the Woods shows three subdivisions,. The lower strand is occu- 
pied by plants which sn grow in strand pools: viz., Aphanizomenon flos-aquae, various Cyano- 
phyceae and Chlorophyce The mid strand vegetation consists of three types defined with 
reference to adaptation = eilig winds I) Prunus Association, which consists of Prunus 
pumila, Lathyrus maritimus, Populus einen. Juncus articulatus and Salix fluviatilis abundant 
as secondary plants, 2) Cornus association, where Cornus Baileyi, C. sericea, Convolvulus 
ee Oenothera biennis, Se angustifolium are the prevalent plants. 3) Salix Associa- 
ion which is constituted b e commingling of Salix fluviatilis as dominant plant with Salix 
Be S. nigra, S. amyg ide and Chenopodium album, Polygonum ramosissimum. The back 
strand is commonly marked at Lake of the Woods by a considerable rise in elevation. Here occur 
in various associations a great variety of herbaceous shrubby and arborescent species? 
Dune Formation. The shore of Lake Michigan between St. Joseph and 
Frankfort for a distance of 250 kilometers is fringed with a narrow belt of 
dunes which tend to close up the mouth of the rivers emptying into the lake 
with the formation of small lakes behind the dunes. Many of the dunes of 
northern Michigan are found on the top of steep bluffs and perhaps were formed 
when the lake water was at a higher level. The dune formers are plants 
adapted to such situations, viz., Ammophila arenaria, Agropyrum dasy- 
stachyum, Elymus canadensis, Calamagrostis longifolia, while certain shrubs 
are equally important: Salır adenophylla, S. glaucophylla, Prunus pumila, 
Cornus stolonifera, and two trees: Populus monilifera and balsamifera. These 
dune forming plants which give rise to various dune forms according to the 
species concerned are not the only tenants of the beach dunes. Most of the 
plants that grow on the upper beach are also frequently present on the dunes. 
A second type of dunes are those which grow slowly. Here occur such 
plants as Andropogon scoparius which forms rounded hills of sand, Arctostaphylos 
uva-ursi and Funiperus Sabina, Funiperus communis, Gaylussacia resinosa, Hud- 
sonia tomentosa, Poa compressa assist in holding the sand. The established, 
or fixed dunes result when after the sand has been captured by the above 
mentioned herbs and shrubs they are tenanted by, or culminate in forest vege- 
tation. 
This succession is typically represented at Cedar Point, Ohio, along Sandusky Bay. The An- 
ee on held dunes are invaded by Prun virginiana, Juniperus virginiana, ea is nee sen 
folia, Arctostaphylos uva-ursi, Ptelea trifoliata, Tecoma radicans, Rhus arom and with such 
of secondary importance as Gleditschia triacanthos, Quercus tinctoria, ai ne Prunus 
serotina, Vitis vulpina, Artemisia caudata, Rubus nigrobaccus, Asclepias syriaca, while Panicum 
virgatum, Elymus striatus, Andropogon scoparius are probably left-over plants from the prece- 
ding condition, One of the most noteworthy peculiarities of the Lake Erie dunes is the relatively 
large percentage of lianes which preserve the integrity of the dune ne wind action, 
1) MacMiıLLan, ConwArY: Observation on the Distribution of Plants along Shore at Lake of 
Woods, Minnesota Botanical Studies Bulletin 9, Parts X XI: 949. 
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