MAJOR VEGETATION OF LAKE OKDBOJI 
95 
conditions. There is usually a relatively barren zone of shifting 
sandy bottom into which creep a number of seed plants, Pota- 
mogeton Richardsonii^ F. pectinatus, Naias, Elodea, Vallisneria, 
etc. Such shores soon deepen off into the bay-formations contain- 
ing Potamogeton amplifolius, P. praelongus, P. natans, F. sosteri- 
folius^ Ceratophyllum, Myriophyllum, Ranunculus, etc. 
Depth plays a most important part,— light probably being the 
determining factor. About fifty per cent of the light falling on 
open water is reflected, and the remainder diminishes rapidly 
through absorption with increasing depth. Most of the species of 
seed plants are eliminated at a depth of twelve feet, and plants 
that flower at the surface may be prevented from setting seed 
at lesser depth than that just given. In Lake Okoboji Cerato- 
phyllum demersufn, discussed briefly below, is the conspicuous 
plant at depths greater than seven or eight feet. It forms exten- 
sive beds, where the bottom is favorable, at depths ranging from 
six to ' nearly twenty feet, ending rather abruptly at about the 
latter depth. It is limited to areas with soft bottoms, and in such 
situations is a most efficient and successful plant. According to 
this preliminary survey Ceratophyllum occupied about 700 acres 
of the bottom of Lake Okoboji in 1919. The accompanying map 
has the Ceratophyllum beds marked by small circles. 
Ceratophyllum demersum forms great masses of vegetation in 
Millers Bay, Emerson Bay, and at the north end of the lake. 
Lesser beds occur in Smiths Bay, and Haywards Bay. A glance 
at the map shows that it forms a narrow zone most of the way 
along the west side of the lake except on convex shores and the 
barren stretch from Elm Crest to Gull Point.' The east side of 
the lake below Haywards Bay shows relatively little Cerato- 
phyllum, due to the abrupt slope and stony bottoms. 
It will be noted that Ceratophyllum thrives only on shelving 
shores and in bays ; in such places sufficient mud may accumulate 
to insure a soft bottom. Ceratophyllum has no roots but modified 
branches are buried in the soft substratum, and afford feeble 
anchorage. The plants have a specific gravity only slightly less 
than water even when fully active in midsummer. The stems 
sink in water but the buoyancy of the leaves keep the plants up- 
right. Detached plants, however, will not float on the water. 
Recalling their ability to grow at considerable depths it will be 
seen that they are relatively unharmed by wave action. Follow- 
ing heavy storms it is the rooted plants rather than the rootless 
Ceratophyllum that are thrown up on the beach. 
