130 Wisconsin Academy of Sciences, Arts, and Letters. 
the net was also lowered in various localities to a depth of about 
25 feet and then hauled straight up. Not a particle of Oscil- 
latoria prolifica was found in any instance, but in all of the 
latter collections there was present in large quantities a species 
of Gleotrichia, the little colonies of which could readily be seen 
floating in the lake, with the naked eye, together with a small 
amount of other common piankton forms. 
We are thus struck at once with an important difference in 
the midsummer conditions of Jamaica Pond and Pine Lake. In 
the case of Jamaica Pond, other forms of plant life appear to 
have been practically excluded for years by Oscillatoria prolif¬ 
ica; during the months of July and August, moreover, the 
growth of the alga in this Pond was but somewhat decreased 
from the earlier more luxuriant development. In Pine Lake, 
on the other hand, we have in midsummer an abundance of an¬ 
other species of blue-green alga, and the seeming total disap¬ 
pearance of Oscillatoria prolifica. This last fact is to me inex¬ 
plicable, since one can hardly conceive of the killing off entirely 
of the luxuriant growth of the past year by the severity of the 
winter cold. I think that it is more than probable that repeated 
observations will surely reveal this species of Oscillatoria again 
during another season, if not later during this one. There is 
thus presented by Pine Lake a most interesting problem involv¬ 
ing the seasonal variation and the varying predominance of dif¬ 
ferent plankton forms. 
When we try to obtain insight into the conditions of the past 
season which allowed of the production of Oscillatoria prolifica 
in such phenomenal abundance, we at once note the unusually 
favorable weather conditions of the latter part of last year. 
According to data kindly furnished by Mr. J. L. Bartlett, 
Weather Observer, while last October at Madison was about the 
average in temperature, November, on the other hand, was 6° 
warmer than usual. During the month of October 1904, which 
had a mean temperature of 51° F., several warm spells were re¬ 
corded at Madison; on Oct. 1, 72°; Oct. 9, 77°; Oct. 17, 75°. 
On Nov. 3, the temperature reached 68°; on Nov. 19, 67° ; while 
the mean for this month was about 40° F. But the most strik¬ 
ing weather conditions of this time were furnished by the long 
