ROOTED AQUATIC PLANTS IN LIMNOLOGY 



111 



111 lakes of the Rocky Mountains that are fed 

 by glaciers or snow fields, the veg-etation is 

 nsiially absent or very scarce. Here the 

 extremely cold water may be a factor in the 

 absence or restriction of the rooted hydro- 

 phytes similar to the observations of Magnin 

 (1893). It is also true that these lakes are 

 rocky and conld sn]-)]-»ort but few plants, or 

 they are rapidly silting with rock flour, 

 which equally prevents plant growth. 



The same retarding effect of latitude, that 

 is evident upon land vegetation, is also 

 observed in aquatic plant communities. Tlie 

 acpiatic vegetation of the higher latitudes 

 is seasonally slower in its development than 

 that of the lower latitudes. 



"When the first cooling of the lake water 

 is observed in the autumn a sharp change 

 takes place in the aquatic vegetation. It 

 quickly loses its thrifty appearance, and 

 before the fall turnover of the lake water is 

 well under way, most of the vegetation has 

 disappeared or rotted. As far as the writer 

 is aware, no extensive study has been made 

 of the relation of temperature to the groAvth 

 of aquatic plants. 



Soils 



The importance of soils in the ecology 

 of rooted aquatic plants is uoav thoroughly 

 appreciated. Pond (1905), Brown (1911), 

 Veatch (1933), and Wilson (1935, 1937) in 

 this country and Pearsall (1920, 1921, 1923, 

 1925, 1929) in England have demonstrated 

 the importance of soils in the physiology of 

 the aquatic plant, or in the development of 

 hydrophyte communities. 



'Pond (1905) and Brown (1911) demon- 

 strated, after experimenting with numer- 

 ous aquatic genera possessing roots, that 

 they grew better if rooted in soil than if 

 suspended over it, or rooted in clean washed 

 sand. 



Pearsall and Pearsall (1923) found that 

 the leaf-shapes of Potamogcton perfoJiatus 

 and P. pmclongus varied sufficiently on dif- 

 ferent soils to suggest that the proportion 

 of lime in the soils is an important factor 

 in determining the leafshape of these spe- 

 cies, and that varieties in P. pcrfoliatns are 

 onlv growth forms. Pearsall and Hanbv 



(1925) further investigated the variation 

 of leaf form in P. pcrfoUatus and concluded 

 that the extreme variability of leaf form 

 is due to the variations under natural 

 conditions of (1) the light intensity and 

 duration, (2) the calcium content of the 

 soil, and (3) the ratio of potassium (and 

 monovalent ions generally ?) to calcium in 

 the soil if little calcium is present. 



Veatch (1931, 1933), working in the state 

 of Michigan, studied the subaqueous soils. 

 He proposed a classification of these and 

 made observations on some relationships 

 between water plants and the water soils. 



Below, only the portion of Veatch 's clas- 

 sification of water soils that is applicable 

 to fresh-water lakes is given. 



I. Lacustrine group. 



AI. Shallow aqueous horizon (tentatively re- 

 stricted to less than 10 feet). 

 A. Calcic water. 



1. High calcic or hard water (14 + 

 grains per gallon hardness). 



a. Sand subaqueous horizon. 



Clean sand compact. 

 Sand-organic matter admixed. 

 Sand-shells or marl admixed. 



b. Clay-colloid subaqueous hori- 

 zon (largely inorganic). 



Dark colored muds. 

 Gray-green muds. 

 Eeddish muds. 



c. Slime or ooze (largely organic 

 and gelatinous or pasty in con- 

 sistency) . 



Black or lirown. 

 Gray-green. 



d. Peat subaqueous horizon. 



Soft or fluid. 

 Compact or matted. 



e. Marl subaqueous horizon. 



Soft or oozy. 



Compact. 



Nodular or peldjly. 



f. Gravel-boulder bottom. 



g. Hard rock bottom. 



2. Medium calcic water (6 to 13 grains 

 per gallon hardness). 

 (Subdivisions same as under high 

 calcic waters.) 



3. Low calcic and soft or acid Avater 

 (6 grains per gallon hardness). 

 (Subdivisions as above except ''e".) 



The general conclusions at which Veatch 

 arrived after visiting about 300 widely dis- 

 tributed localities in Michigan are the fol- 



