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s 



1902] SURVEY OF THE HURON RIVER VALLEY 135 



{^d) Hydrodyna7mc factors^ referable to the action or presence 

 of water. Small waves are created in the lake by high winds 

 which would eat away the light soil composing the shores but 

 for the fact that such shores are everywhere protected from 

 wave action by a border of water lilies {^fig. 2). Even in winter 

 this action is prevented because the dead leaves remain in situ 

 until the next year. The current of the brook entering from the 

 southeast sweeps away or covers with gravel the accumulations 

 of detritus at that point ; as a result, Nuphar and its associates 

 are not found there [^fig* j). Aside from this local influence 

 hydrodynamic factors at the present time are so limited in their 

 action that they may be disregarded. 



(^) EdapJdc factors^ depending upon the nature of the soil. 

 The humus in the soil formed by the decayed vegetable sub- 

 stances renders it very favorable for plants of the Nuphar, 

 'Typha, and Carex types. The presence of water saturated with 

 organic matter in solution plainly influences the character of the 

 vegetation. If Schimper's view ? of the effect of humic acid be 

 correct, the explanation of the xerophytic character of some of 

 these swamp plants is that the soil is practically undrained and 

 water with which it is saturated is rich in organic acids. 



A microscopic examination of the soil from the deep basin 

 of the lake shows that it is almost entirely composed of finely 

 ■comminuted, bluish-gray clay with a very few particles of organic 

 debris. The soil from the Nuphar zone is largely composed 

 <^f fragments of epidermal tissue, moss-stems, diatom shells, 

 bast fibers, grains of sand, and crystals of calcium carbonate 

 from Chara. Chemical analysis shows that nitrates and 

 nitrites are not present in the soil, while phosphates are more 

 ■abundant. 



That portion of the lake bottom which is covered with soil 

 ■of a calcareous or arenaceous nature does not seem favorable to 

 the growth of the characteristic plants of the lake; the only 

 ■ones which grow upon such soil are Potamogeto?i zosteraefolius and 

 ■a few blue-green algae. Evidently lime-containing soils are as 



'SCHIMPER, A. F. W., Pflanzengeographie, p. 18. 



