ROOTED AQUATIC PLANTS AND THEIR RELATION 

 TO THE LIMNOLOGY OF FRESH- 

 WATER LAKES 



By L. R. WILSON 



COK COLLEGE, CEDAK KAPIDS, IOWA 



The Eooted Aquatic Plants as a Bio- 

 logical Group 



If Ave examine the rooted liydropln'tes as 

 a biological group, we are impressed by the 

 fact that they come from practically all 

 parts of the vascular plant kingdom. The 

 Pteridophytes contribute members from the 

 genera Equisefum, Isoetes, and tlie water 

 ferns. The monocotyledons which contrib- 

 ute great numbers of species are from the 

 genera Typha, Sparganuim, Potamogeton, 

 Zostera, Najas, J uncus, Sogiftaria, Alis))i(i, 

 Elodea, Anacharis, and VaUisnera, as well 

 as some grasses and sedges. The dicotyle- 

 dons are represented by such families as the 

 Buckwheat, Hornwort, Water Lily, Crow- 

 foot, AYaterwort, Evening Primrose, AVater 

 Milfoil, Parsley, Primrose, Convolvulus, 

 Figwort, Bladderwort, Lobelia, and Com- 

 posite. 



Such an assemblage of families and gen- 

 era from all parts of the vascular plant 

 kingdom, except from the Gymnosperms, 

 raises the question of origin for these hy- 

 drophytes. It is sufficient to state here that 

 there is reason to believe that the Angio- 

 sperms, at least, were originally terrestial 

 and that some members have become semi- 

 aquatic or entirely aquatic. 



The close relationship between the anat- 

 omy of the hydrophytes and the waters in 

 which they live is not only of prime impor- 

 tance to the plants in question, but is also 

 important to those smaller plants and ani- 

 mals which depend upon them for support, 

 protection, or food. Probably the most 

 important modification in their anatomy is 

 the development of spongy tissues called 

 aerenchyma. These tissues provide air 

 spaces in the various parts of the plants, 

 and serve in various capacities in their 

 physiology, and in the life histories of the 



invertebrates which live upon them. Most 

 of these plants are perennial, and coupled 

 witli their more or less uniform environ- 

 ment, tend to produce somewhat permanent 

 communities of plants and associated ani- 

 mals. Therefore, a more static ecology is 

 likely to exist in water than on land. 



The Geologic and Physio-chemical 

 Factors 



It is common knowledge that tlie geology 

 of any particular region determines the 

 soils and the characteristics of lakes which 

 are formed in it. The soils which have 

 evolved from the bedrock, or from the ma- 

 terials that have been variously trans- 

 ported to a particular region and modified 

 by climate, determine to a large extent the 

 vegetation of the region. This statement 

 applies to both the vegetation of the land 

 and of the water. 



The relationship of bedrock to lake 

 chemistry appears to be well illustrated in 

 Wisconsin. An examination of the geo- 

 logical map of that state shows a large area 

 in the southern part to be covered by lime- 

 stones, while in the northern part there is 

 a smaller area where granites are exposed. 

 It may be generally stated that the lake 

 waters upon the limestones are harder than 

 those upon the granites. This difference of 

 lake waters may also be a direct reflection 

 of the glacial drifts in regions where the 

 bed rocks are deeply buried. In regions, 

 as in north central Wisconsin, where the 

 glacial drift is derived largely from acid 

 rocks, the lake waters are softer than in 

 regions where the drift is derived from 

 limestone. Lakes that were formed by some 

 geologic agent which left the bed or basin 

 developed on solid rock, or with little or no 

 fine clastic material, show different physical 

 and chemical characteristics than those that 



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