Rickett—The Larger Aquatic Plants of Lake Mendota. 511 
other. This would have been an impossible task in the time avail¬ 
able. It was fairly easy, however, to separate P. zosterifolius, P. 
amplifolius, and P. Richardsonii. The differences between these 
three species are very apparent in the shape and size of the 
leaves. The two narrow-leaved species, P. pectinatus and P. in¬ 
terior, were grouped together. Of these, the former is by far the 
more abundant; the second occurs in scattered patches in deep 
water. Another species which is found occasionally is P. lucens, 
which is a broad-leaved form, but readily distinguishable from P. 
amplifolius and P. Richardsonii . Mixed with this there may have 
been a little P. alpinus, which has been reported by Denniston in 
Lake Mendota. 
The plant listed as Heteranthera dubia could not be identified 
with certainty. It does not appear in any previous lists of plants 
found in the lake. It is found in comparatively small quantities, 
and was at first confused with Potamogeton zosterifolius. The 
discovery of the fruits in the axils of the leaves proved this to be 
an error, but by this time the plant was well past its prime, flowers 
could not be found, and identification was impossible. It answers 
to the general description of Heteranthera more nearly than to 
that of any other plant. 
The first ten and the last two species in the list compose the 
bulk of the vegetation of the lake. The other species are found 
only in scattered patches, chiefly in the shallow bays and mouths 
of streams. One plant, Elodea camadensis, is listed although it 
was found only in minute quantities in the samples. This species 
is abundant in the streams that flow into the lake, especially in 
that which empties into University Bay. 
In some places there was an abundant growth of floating and 
attached filamentous algae (notably several species of Spirogyra). 
This was found mostly on muddy shores and in the bays. It was 
impossible to separate this from the larger plants, and in some 
cases it made the separation of the latter impossible, so that no 
account can be given of the amount of this algal growth in the 
lake. In other cases, some plants, especially Potamogeton pectina¬ 
tus and Najas flexilis, were covered with globular masses of a 
blue-green alga, Gloeotrichia, which also was impossible of separa¬ 
tion. These algae, of course, disturb to some extent the values 
for the weights of the plants with which they were found. 
The Yield of the Plant Zone. Table 14 represents the total 
weights of all species, brought together from the ordinary plant 
