THE VERTICAL DISTRIBUTION OF VOLVOX IN THE 
PLANKTON OF LAKE MONONA 
Gilbert Morgan Smith 
On the morning of July 6, 1916, Messrs. Birge and Juday, of the 
Wisconsin Geological and Natural History Survey, noted a very 
peculiar condition, while collecting plankton samples from Lake 
Monona, Madison, Wisconsin. They found that there was a very 
decided stratum of Volvox colonies at a depth of three meters, while 
above and below this stratum the colonies were very scarce. Mr. 
Juday called my attention to this condition, and suggested that I make 
plankton catches at various times of the day to see if the position of 
the belt changed. Although the data presented herewith are, at best, 
fragmentary, they seem worthy of record since nothing is known con- 
cerning the vertical distribution of Volvox as a limnetic organism. 
The "bloom " of this alga is so sporadic that it may be some time before 
so favorable a condition for a study of this kind again presents itself. 
The ordinary method of pumping a measured amount of water 
(ten liters) from a desired depth and then straining through a filter 
net was used for collecting the samples, which were then preserved in 
alcohol until counted. In counting, the volume of the catch was 
reduced to ten cubic centimeters, then a one-cubic-centimeter sample 
was taken, put in a trough, and the number of colonies counted through 
a binocular microscope. 
The station where the alga was first discovered is about a kilo- 
meter northwest of Winnequah point, at the deepest part of the lake. 
My samples were collected about a half kilometer out from the Wirka 
Boat Livery where the water is between ten and thirteen meters deep. 
This station is about a kilometer and a half from the deepest part of 
the lake. Sunset occurred at 7 140 on July 6 and the sample from the 
surface was taken at 7 45. Since it takes about five minutes to adjust 
the hose, pump the water, label and preserve the sample, the interval 
between two catches is about five minutes. The same order was fol- 
lowed in every case, the first sample taken at the top and others on 
down at intervals of a meter. Twilight lasts about an hour at this 
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