VERTICAL DISTRIBUTION OF VOLVOX 
179 
season so that it had been dark for nearly an hour when the next series 
of samples was collected at 9:20 P.M. The following morning the sun 
rose at 4:26 and the first catch was made at 4:25. A series of samples 
was collected every succeeding hour until 8:30 and then at 10:00 and 
again at noon. Collecting was resumed at 5:30 A.M. the following 
day and continued at hourly intervals until 9:30 A.M. when the sky 
became cloudy and a sharp squall blew up. The wind caused con- 
siderable wave action, so that what vertical distribution there had 
been was disturbed. The results of these collections are shown in the 
following table. Those of the last day's collecting are not incorporated 
since practically no colonies were found. 
Table I 
Number of Colonies per Liter at the Various Depths 
Depth 
in 
Meters 
July 6 (Evening) 
July 7 (Morning) 
7:45 
9:20 
4:25 
6:30 
7:30 
8:30 
10:00 
12:00 
0 
I 
2 
3 
4 
5 
6 
890 
1,200 
4,39c 
33,200 
2,790 
1,900 
820 
1,620 
2,300 
11,300 
9,010 
3.980 
670 
10,810 
5,840 
9,600 
3,150 
810 
11,500 
12,400 
17,500 
7,700 
1,290 
10,100 
15,500 
5,800 
1,670 
650 
8,600 
24,500 
12,500 
2,130 
590 
13,800 
19,300 
10,900 
1,280 
1,250 
14,300 
13,300 
5,230 
3,560 
840 
28,100 
14,600 
2,100 
980 
510 
The weather conditions, at the time the collections were made, are 
important factors. Had there been any wind stirring up the water 
the vertical distribution would have been affected. Since the 6th and 
7th were exceptionally calm days this factor may be neglected. The 
following meteorological data have been furnished by Mr. E. R. Miller, 
the Local Forecaster of the Weather Bureau. The meteorological 
observations are taken at a point about forty-five meters above the 
level of the lake where there is always a greater air movement than on 
the lake surface. Shaw (8) gives methods of estimating the velocity of 
the wind so that the weather conditions of the 6th and the 7th may be 
easily visualized.^ Both of these days were bright and sunny, the 
1 When the wind is blowing at two miles per hour the direction of wind is shown 
by smoke drift, but not by wind vanes; at five miles per hour the wind is felt on the 
face, leaves rustle, and ordinary weather vanes move; while at ten miles per hour 
leaves and small twigs are in constant motion and the wind extends a small flag 
(P- 31). 
