Rickett—The Larger Aquatic Plants of Lake Mendota. 513 
Potamogeton zosterifolius, appears only in the two deeper zones. 
In the deepest zone, the number of species present is still smaller. 
Chara, Lemna, and Heteranthera are no longer found. Vallis- 
neria here forms a lower percentage of the total, and Potamogeton 
amplifalius composes about half of the entire flora. An interest¬ 
ing incident in this zone is the occurrence of several patches 
(stations 40, and 41) of the latter plant growing very luxuriantly 
and reaching the surface in 4 meters of water. All other 
species, except P. zosterifolius, are present in smaller relative 
quantities than in the shallower water. 
The proportion of these plants varies slightly according as the 
wet or the dry weight is under discussion, owing to the fact that 
the different species vary considerably in their water content 
(table 3). When, however, all species are taken together, as in 
table 9, in a comparison between the different zones, this varia¬ 
tion is corrected, and wet and dry weights form practically the 
same percentage of the total. 
Variation in Amount and Kind of Vegetation . The data pre¬ 
sented in the two preceding sections have reference to averages, 
which, of course, conceal a great deal of regional variation. The 
latter is especially marked in the shallow waters of the lake. 
For instance, sample 74, station 8, was collected from an 
area of 3 square meters, but yielded a total wet weight of only 
100 grams, composed of Najas and Chara. Such almost barren 
regions are found here and there in places where there is an ex¬ 
tensive sandy shallow region. On the other hand, there are places 
correspondingly much more productive than the average. Sample 
116, station 37, shows a wet weight of 1,300 grams from an area 
of 0.3 square meter. The shallow bays also rank high in yield 
(table 10), producing many plants, especially emerged plants, 
not found elsewhere in the lake. Local variation exists not only 
in the amount, but also in the character of the vegetation. Refer¬ 
ence to table 2 will serve as an illustration. Among the first six 
samples of the station, all coming from about the same depth, 
there is a marked variation in the species of which they are com¬ 
posed, though most of them contain the predominating species, 
Potamogeton pectinatus and P. Richardsonii. 
In water from 1 meter to 3 meters deep, there is much more 
uniformity both in quantity and in character within a station, 
but between the different stations there are considerable differ- 
33—S. A. L. 
