70 



freezing of Lake Morat in 1825 in which the ice was colored by Oscilla- 

 toria rufescens. 



Klausener ('08) made a study of the so-called "Blutseen" of the 

 High Alps. Most of these were colored by Euglena sanguinea Ehr. 



TABLE SHOWIXG THE MEAN TEMPERATURES FOR OCTOBER AND NOVEMBER. 

 DURING THE DECENNIUM 1908-1917. 



Station: Winona Lake, ten miles front Huffman's Lake. 



The appended table of temperatures* indicates that the mean for 

 October, 1917, was 5.6 degrees F. lower than for any other October in 

 the ten years preceding, and 9 degrees F. colder than the mean for this 

 decennium. This means that the lake was cooled early in the autumn 

 and remained at a rather low temperature for six to eight weeks instead 

 of the normal, much .shorter, period. That is, arctic conditions main- 

 tained in this lake for nearly two months. This is, I think, one of the 

 factors that caused this alga to develop so luxuriantly. 



Against this view, are the observations of Hyams and Richards ('01, 

 '02, '04), and others on 0. prolifica in Jamaica Pond. Here the max- 

 ima occurred in the warmer months, although a dense growth often de- 

 veloped just before the ice formed. 



In the present state of our knowledge it is impossible to harmonize 

 these observations with those on the so-called "blood lakes" of the Alps, 

 those of Olive (loc. cit.) and the ones here presentd on Huffman's lake. 



Brunn ('80) suggests the presence of iron compounds as one of the 

 conditions for the development of red pigment in the blue-green algae. 

 This condition is satisfied by the large amounts of iron oxide in the afflu- 

 ent springs at its margin. 



•These temperatures are for the Winona Lake Station, wliich is about 10 miles cast of Huff 

 man's Lake. 



