242 Brown : Algal periodicity 



studied except in two places, the smaller of the water-works ponds 

 and in the lower part of stream no. I. This class of plants seems 

 to thrive best in impure water. The water-works pond just men- 

 tioned, taken as a whole, contains relatively pure water, but at one 

 corner near the pumping station it was very impure, due to the oil 

 and refuse from the pumping station flowing into it. Here there 

 was always a good amount of the Cyanophyceae to be found 

 growing. From this place they floated out and settled around 



the edge of the whole pond. 



Two 3pecies of Nostoc appeared in the territory studied, N. 

 verrucosum and N. commune. N. verrucosnm persisted through- 

 out the year in stream no. I with very little change. At times it 

 appeared to be less abundant but this was due to the water wash- 

 ing away a part during floods. It was attached to the stone bot- 

 tom of the "branch" in the swifter parts. It grew up in hollow 

 subglobular masses five or six centimeters in diameter. They 

 were at first pale yellowish -green, rather firm, jelly-like masses, 

 but the outer part soon became incrusted with lime so as to make 

 it harsh and crusty. Soon after reaching this stage the flow of 

 the water caused them to break loose and float away. No hetero- 

 cysts or spores were noticed. 



A small amount of A r . commune was found growing on the 

 damp soil along the edge of pond no. 3, September 20, 1906. The 

 region was covered with water at my next visit and none of the 

 alga was found. The same species was found growing in a similar 

 place along the upper part of stream no. 1, October II. It con- 

 tinued to grow here and was rather abundant until the middle of 

 November, when it disappeared. 



Scattering filaments of Anabaena were found at various times 

 during the year in material collected in the lower part of stream 

 no. 1, pond no. 1 and the smaller of the water-works ponds, but 

 no attempt was made to trace the periodicity. 



Three different species of Oscillatoria appeared in considerable 

 abundance in the ponds and streams under observation. These 

 were Oscillatoria tenuis, 0. limosa and 0. princeps. Some other 

 species were noticed but they did not persist any length of 

 time. 0. tenuis was the most abundant form both in quantity and 

 distribution. It was abundant in stream no. I, especially in the 



