380 Wisconsin Academy of Sciences, Arts, and Letters. 
made up of sand and of finer pebbles. Physically, bars are 
continuous with shores, are subject to the same conditions, 
and are therefore included under that head. The shore is de¬ 
void of vegetation, except the plumes of the alga Cladophora 
on rock and gravel. 
Plant Zone .—The plant zone in Lake Mendota extends from 
the breaker line to a depth of hardly more than 6 meters, as 
a whole not exceeding 5 meters. The upper delimitation is 
the rachion in the steep parts of the littoral area, but it is 
rather less marked in the shoals; yet even there the shore 
proper and the breaker line are always barren, and the vegeta¬ 
tion between rachion and beach is comparatively scant. 
In many lakes there exists a definite plant zonation. There 
may be a succession of areas characterized by the dominance 
of some plant, e. g., Lemna, Chara, Myriophyllum, etc. In 
Lake Mendota there is but one spot, where such a zonation is 
at all indicated. This is a small area along the western end 
of the bar in University Bay. Here a zone of pure Chara is 
followed by submerged hummocks of Lemna, this in turn by 
Myriophyllum and Ceratophyllum, and finally by Potamogeton 
amplifolium. Small areas may be found in other portions of 
the lake where some plant species may attain a slight domi¬ 
nance, as Chara does opposite Merrill Springs; but a true zon¬ 
ation is entirely absent. 
There is, however, a secondary zonation, not so much of 
plant species, as of types of plants. This consists of a zone 
of “upright’’ or standing vegetation, e. g., Potamogeton ampli¬ 
folium, Najas, and Vallisneria, which tend to reach the sur¬ 
face (but do not emerge); and a zone of “recumbent” vegeta¬ 
tion, composed of Chara, Myriophyllum, Ceratophyllum, and 
some Potamogeton species, all of which tend to recline. 
As incidental, but of direct ecological importance, the heavy 
incrustation of carbonates on the leaves of Potamogeton and 
Vallisneria should be noted. After some days of quiet 
weather the leaves of these plants are covered with a layer of 
lime, which breaks off in heavy weather and is swept to the 
bottom. In places the bottom is covered with a very appre¬ 
ciable deposit of this “plant marl.” It forms a type of bot¬ 
tom which is little frequented by animals. 
Shell Zone .—The lower limit of wave action is marked by the 
shell zone. In Lake Mendota this also marks the lower limit 
