Olive—Occurrence of Oscillaioria Prolifica. 131 
drought which then prevailed; so that possibly this also assisted 
the favorable conditions for algal growth. The large lakes at 
Madison, Monona and Mendota, froze on Dec. 13 and 14, 1004, 
respectively. I have no record concerning Pine Lake, but it is 
quite probable that it was frozen over at about the same time, 
notwithstanding the fact that it is considerably smaller than 
the Madison lakes. The likelihood of the earlier freezing of the 
smaller lake is somewhat counterbalanced, in this instance, by 
the fact that the climate of the locality of the latter is to a cer¬ 
tain extent influenced by the proximity of Lake Michigan, since 
it is only 20 miles aw T ay from the large lake, and over 50 miles 
nearer than Madison. 
Now, granting that the conditions for the growth of Oscilla- 
toria were unusually favorable in Pine Lake particularly dur¬ 
ing last October, how can we account for the occurrence of 
such vast quantities of the alga, frozen up in the ice? ITyams 
and Richards speak of an occasional fall growth, a sort of reju¬ 
venescence due to a new warm season, which, resulted in one in¬ 
stance in some of the alga being found in the ice. Birge (98, p. 
420) says that in the autumn there is normally “a period, be¬ 
ginning a little before the first of October and extending to the 
freezing of the lake, when the algae are present in immense 
quantities, and are distributed with approximate equality 
through the whole mass of the water.” If those observers were 
correct, who assert that the first ten inches of the ice from Pine 
Lake was clear, and the alga appeared only in the lower strata, 
then we must assume that, after considerable freezing had been 
accomplished, the severe cold must somehow have killed the alga 
and thus caused it to rise to the surface. I have not, however, 
myself seen an instance in which one side cnly of the ice-cake 
was colored, but those which I examined were instead reddish in 
small areas, about cracks and air-bubbles. It has been suggested 
that possibly those who made the observation recorded above 
were mistaken and that it was the upper part of the ice which was 
thus colored and not the lower; I have not had an opportunity, 
however, of verifying this suggestion. But in the event of this 
being the case, then we must suppose that the unusually mild and 
long-prolonged growing season of last fall culminated in a 
‘‘blooming time,” or “working,” of the alga. Should this prove 
