394 Wisconsin Academy of Sciences^ Arts, and Letters. 
Chara, with small amounts of Potamogeton heterophyllus, Naias, 
and Vallisneria; the other contains great quantities of the larger 
Potamogetons, often in addition to large amounts of Chara. The 
shallow water is most often of the first type. The deeper water is of 
the latter sort, grading out into almost pure Ceratophyllum and 
Myriophyllum. The medium depths vary the most. The species of 
Potamogeton often grow in great abundance mixed with Chara, 
Ranunculus, and others. Chara, as already mentioned, frequently 
grows alone in large patches. Drepanocladus also, in the few 
places where it attains abundance, grows in large patches almost 
unmixed with other plants, except that scattered stems of Myrio¬ 
phyllum are often found arising from it. There are in several 
stations absolutely barren patches irregularly distributed amidst 
luxuriant vegetation. 
In some places samples of great weight were obtained. The 
largest came from Station 21, and yielded 2,700 grams (wet) from 
0.25 square meter. There were several others almost as big. They 
were composed for the most part of Chara. There is, as far as I 
know, no single spot in Lake Mendota which yields as much as 
this. The smallest sample collected weighed 30 grams (wet) from 
0.5 square meter. Most of the samples weighed about 200 to 300 
grams (wet) from 0.25 square meter. In Mendota the general 
average was somewhat higher. 
General Discussion 
\ 
Aside from its presentation of the quantitative data, this paper 
cannot do much more than suggest the ecological problems that 
await the botanist in this field. Pearsall (2) has attacked similar 
questions in the English lakes and in an excellent paper presents 
important evidence on the nature of the environmental factors 
that affect submerged vegetation. He considers that light is im¬ 
portant only insofar as it limits the downward extension of the 
flora and that temperature has little effect in determining the kind 
of vegetation, at least within the limits found in one lake. Most 
of the variation in the kind of vegetation proves to be connected 
with soil differences, which often correspond to differences in their 
physical characteristics. 
Nothing has as yet been done on Wisconsin lakes which is com¬ 
parable to Pearsalls correlation of soil composition and type of 
vegetation. With regard to the other factors, light and tempera- 
