508 Wisconsin Academy of Sciences, Arts, and Letters. 
a station were then grouped together according to the zones in 
which they were gathered, and for each zone, within the station, 
the average weight, wet and dry, of each species per square me¬ 
ter was calculated. 
Not all zones were thus treated in all stations. In some places, 
e. g., stations 1 and 13, the slope of the shore is so steep that there 
is practically no shallow zone, the vegetation at the water’s edge 
being composed entirely of Cladophora. Not so many samples 
were obtained from the deepest zone as from the others, owing 
partly to lack of time, and partly to the fact that the growth here 
is comparatively uniform, so that fewer samples were necessary 
in order to obtain an average. 
Weight per Square Meter of Zones. Considering, then, one 
zone as a whole, the average weight per square meter was com¬ 
puted from the values calculated for that zone in each station. 
For this purpose, the portions of the zone within the various sta¬ 
tions were first grouped according to the type of bottom found, 
and the average weight per square meter calculated for each type. 
Two types of bottom may be distinguished, consisting of sand or 
gravel, or of mud. A third type is found only in one place (sta¬ 
tion 34). Here there is a floor of clean rock, entirely barren. 
Only in rare cases is there a clean sand floor, and there are all 
gradations from this to one of pure mud, with varying amounts 
of gravel or rocks; the characterization of each station as ‘ ‘ sandy ’ 1 
or “muddy” means, therefore, that it is more sandy than muddy 
or vice versa. Within one zone in one station the bottom is prac¬ 
tically constant, and, of course, there is a gradual transition into 
the next type. These differences, with the above noted limita¬ 
tions understood, are represented on the map. 
All three zones were handled in this way. It should be borne 
in mind that the grouping of stations according to their soil char¬ 
acter has reference only to the zone then under consideration; 
the zones themselves may be different in this respect within a 
single station. The results of these calculations are shown in 
tables 4, 5, and 6. The average weight per square meter of all 
species taken together is obtained by adding together the figures 
for the individual species in each case. 
In calculating the average weight per square meter for a whole 
zone, no account was taken of station 34, since the area of this 
station is so small when compared with the total of that of the 
other 40 stations. 
