94 
IOWA ACADEMY OF SCIENCE Vor.. XXVII, 1920 
water except in the most sheltered places. All free floating plants 
in the open lake are soon beached, where they die. 
Most of the plants are fairly constant in their expression in 
the open lake, having definite relations to depth, substratum, and 
exposure to wave action. But some of the above list are typically 
pond plants which in the lake proper do not find favorable habi- 
tat. Heteranthera and Blodea might be cited as examples and 
these are sometimes encountered in the most unexpected places. 
The former has not been noted flowering at the surface of the 
water in Lake Okoboji though it sets seeds regularly through a 
cleistogamous pollination. The species of Blodea could not be de- 
termined in many cases as it flowers sparingly in the open lake 
while blossoming profusely in the ponds and shallower lakes of the 
region. All plants noted in bloom were B. ioensis. 
Favorable habitats have well marked formations consisting us- 
ually of a number of associated species having similar require- 
ments. The shallower portion of Millers Bay, partly cut off 
from the larger body of water by a submerged bar, contains an 
assemblage that has remained remarkably constant through the 
ten years it has been under observation. Within a couple of 
hundred yards of the grounds of the Lakeside Laboratory are 
found all the plants noted in the above list for the lake. Each of 
the other major bays would give a similar list, but the less desir- 
able habitats would give fewer species. 
The character of the bottom is of great importance in deter- 
mining the make up of the formations in any given area. In most 
places rocky shores are associated with greater exposure to wave 
action, so it is difficult to weigh, from observation, the relative 
merits of these two factors. Such places have usually more 
abrupt slopes so do not offer anchorage for a zone of plants wide 
enough for much mutual protection. The headlands on the west 
side and much of the eastern side of the lake exhibit these con- 
ditions and are the barer borders. In these regions Chara is a 
prominent and often the dominant plant. The region between Elm 
Crest and Gull Point with similar stretches on other shores pre- 
sent vast Chara beds with relatively few Angiosperms with them. 
Potamogeton natans is very commonly admixed and in many cases 
this is true oi Potamogeton Richardsonii. Certain of the smaller 
and well rooted forms are abundant in the shallow margins — ' 
here are frequently found such as Heteranthera duhia, Naias 
dexilis, and occasionally Zannichellia. 
Sandy beaches on concave shores offer a very different set of 
