69 



the surface of the lake in enormous quantities. It was difficult to make 

 a quantitative estimate of it by the ordinary limnological methods on ac- 

 count of the wind drifting it. Some notion of its abundance may be 

 gained from the following observations: 



At 10:00 a.m. there was still a very heavy fog on the lake. When 

 rowing to the center of the lake the water appeared pink when disturbed 

 by the oars, and in the wake of the boat. By 3:00 p.m. a slight breeze 

 had drifted the algae in a solid scum along the east side of the lake. 

 In the bays this scum reached a thickness of 4-6 mm. The alga when 

 concentrated in this scum had a rather dark brick-red appearance. 



That the alga caused the destruction of the fish is probable on ac- 

 count of two facts. First, it is the only associated extraordinary phe- 

 nomenon. This is of course only presumptive. Second, certain blue- 

 green algae (cyanophycae) seem to produce substances, either by their 

 metabolism or decay, which when concentrated are toxic to vertebrates, 

 and may even cause death. 



Arthur ('83) reports two instances in which cattle were poisoned by 

 drinking water that was covered with a thick scum of blue-green alga 

 (Rivularia fluitans Cohn). 



Nelson ('03) after discussing the cyanophycas that cause "water 

 bloom" closes with these words : "In several instances it has been almost 

 conclusively proved that the presence of one or more of these species in 

 drinking water used by stock has caused fatal results." 



Cause of the Excessive Growth of Alg^. 



This lake has been under the observation of Mr. Maurice Miller for 

 thirty-two years. He reports that this autumn (1917) is the first time 

 that a red scum has appeared. 



Olive ('05) identified this algae from the ice in Pine Lake (Wiscon- 

 sin), where there evidently had been a considerable growth just before 

 the lake froze. 



Red pigment is very characteristic of the plankton of arctic and 

 alpine regions (Steuer 1910, pp. 277-8). The red coloration of lakes and 

 ponds in the Swiss Alps seems to be a rather common phenomenon. 



Brunn ('80) reports the ice on Lake Neuchatel being colored red 

 with a growth of Pleurococcus palustris Klintzig. He also refers to the 



