502 Wisconsin Academy of Sciences, Arts, and Letters. 
Obtaining Samples 
Apparatus. The different parts of the lake were visited by 
means of a small rowboat with an attached motor. In this way 
it was possible to reach all parts of the lake in a short time, and 
to bring back a considerable quantity of collected plants. 
In order to obtain quantitative data, it was necessary to gather 
plants from measured areas of the lake bottom. After several 
more or less unsuccessful attempts to measure under water a plot 
of ground which had been stripped of its vegetation, the follow¬ 
ing method was resorted to: a square frame of galvanized iron 
was constructed, measuring m. on a side, and about 7 cm. in 
height; this was lowered to the bottom, and all plants enclosed by 
it were gathered. This made it possible to obtain samples all over 
the lake from areas of the same size, or differing by simple mul¬ 
tiples, and having a simple relation to the unit of area used, name¬ 
ly, 1 sq. m. This method is subject to some error, inasmuch as the 
frame may include the heads of some plants whose roots are out¬ 
side the measured area, and also inasmuch as it is difficult to pluck 
and save every plant without spending an unreasonable amount of 
time on one sample. 
Another source of error lies in the fact that it is difficult to pull 
up entire plants under water, and therefore the roots were in 
most eases left in the soil. This is more frequently true in muddy 
than sandy soil. 
As the results must be in the nature of an estimate rather than 
an exact calculation, such errors may be considered as compensated 
by the large number of samples—221—which were obtained. 
In water not more than 2 m. deep, the plants were reached by 
swimming, using as a guide the cord to which was tied the meas¬ 
uring frame, and as anchorage a cement block with an inset 
handle, let down near the frame. An area of %. sq. m. could be 
cleaned off in this way in three or four trips to the bottom, de¬ 
pending upon the density of the vegetation. 
In deeper water, a diving hood was used. This was supplied 
with air by a hand pump which could be conveniently carried in 
the boat, and descent and ascent in the water were made easily 
by an anchor line. Depths as great as 7 m. were visited in this 
way. 
The collected plants were placed in galvanized iron boxes, with 
enough water to cover them, and taken to the laboratory where 
