390 Wisconsin Academy of Sciences^ Arts, and Letters. 
plants as in the latter lake, nor, indeed, so well as are the muddier 
parts of Green Lake; nor do they display any species which do 
better there than on mud. The comparative scantiness of their 
vegetation may perhaps be explained by the violence of the waves 
in this lake; but it is interesting that species, such as Potamogeton 
Bichardsonii and'P. pectinatus, which grow decidedly better on 
sand in Mendota, attain their greatest development in Green Lake 
elsewhere than on these few sandy places. 
Calculations 
The data obtained by weighing the plants were treated in much 
the same way as in the case of Lake Mendota. The original weights 
obtained were reduced to common terms—grams per square meter 
—for each sample and all the samples in each zone of each station 
averaged together. The results are shown in tables 3, 4, and 5. 
The values for all the stations of each zone were then averaged, to 
give the weight per square meter of each species for each zone. 
Since the stations were of greatly differing sizes, it was judged 
best not to give them all the same weight in the average. One of 
the smallest stations was selected as a unit, and the other stations 
expressed in terms of this. The average weights in each station 
were multiplied by a factor for the station, its area in terms of the 
unit station, and the resulting figures averaged together, using 
the sum of all the factors as a divisor. The dimensions of the sta¬ 
tions were obtained by measurement on the map. In Zone 1, for 
instance, the area of Station 23 was found to be 9, that of Station 
36 was 6, Station 1 being the unit. The results of these calculations 
are given in table 6. 
There were several plants that did not form part of the main 
plant belt, being found in scattered patches, and yet were present 
in considerable quantities. Such were Scirpus, Carex, Castalia, 
Nymphaea, and Cladophora. Of the first four of these, samples 
were collected in the usual way; the area of the particular spot 
sampled was estimated, in most cases by rowing around it and 
expressing it in terms of boat-lengths. From these data total 
weights were obtained directly. The same method was used for 
Cladophora in some cases, where there were large patches. In 
most cases, the fringe of Cladophora being thin, all of the growth 
for a certain distance was cleaned off, and measurement made of 
the length (instead of the area) of the strip or station from which 
