No. 588] POPULATION OF « BLANKET- ALGM " 753 



Ithaca, N. Y. (see map). They varied from shallow, 

 transient collections of ditch-water to large, permanent, 

 usually stagnant pools. Those lettered B, C, D, G, J, M, 

 and N belong to the first category. Pools x, x 1 , x 2 , x 3 , x 4 , 



and y, y 1 , E, K, I, and L are permanent pools and measure 

 from four to thirty or more inches in depth. Pool H is a 

 quiet part of a large stream. Pools F and A are artifi- 

 cially enclosed and are filled from pipes. The pools of 

 the lowland of Cayuga Valley (about 400 ft. above sea- 

 level) are A, B, C, B, and E. The others are among the 

 hills (about 800 feet above sea-level). 



The Filamentous Algce of the Floating Mass. — Although 

 there was such variety in seasonal conditions and in the 



