The Plankton Algae of the Palisades Interstate Park 119 



There have been, however, several studies that are of interest in 

 shedding Hght on the nature of the plankton flora of artificial lakes. 

 Griffiths ('09) finds that the flora of an old small artificial lake in 

 England contains Volvox (PI. 6, Fig, 8) and Microcystis (PL 3, 

 Figs. 11-13) in small quantity, but thinks that this lake does not 

 develop a true plankton flora. In a later investigation of other 

 artificial lakes from the same region he finds a typical heleoplankton 

 formation with the occurrence of certain Protococcales in consider- 

 able abundance. 



G. S. West's thorough-going survey of the Yan Yean reservoir in 

 Australia ('09) is of particular interest, since he finds a true Cale- 

 donian plankton community. This body of water was formed in 

 1857 when a dam thirty feet high was built across a valley to 

 impound water for a municipal water supply. In this reservoir 

 there are about 120 different organisms, and of these about four- 

 fifths are found in the plankton only. The proportion of the fre- 

 quency of the various species in the plankton and the benthos is 

 not the same, since certain ones occasionally found in the benthos 

 are undoubtedly accidental wanderers from the plankton where they 

 occur in abundance. The great scarcity of blue-green algae in this 

 comparatively shallow artificial lake is also a striking feature of the 

 flora ; and this artificial lake, with a typical lacustrine Caledonian flora 

 that is practically free from blue-green algae, is particularly hopeful 

 in showing that an abundance of blue-green algae is not a universal 

 character of artificial lakes. 



In the artificial " tanks " of Ceylon, Fritsch ('07) has found that 

 the flora is practically that of a normal lake. In these waters the 

 plankton is characterized by a luxuriant growth of blue-green algae, 

 particularly Microcystis, a condition which is explained by the high 

 temperatures and lack of aeration. Fritsch gives no data on the 

 age of these lakes. 



The most intensive study of an artificial lake is that of Kolkowitz 

 ('09, '14) on the " Lietzensee " in Berlin. The site of this lake was 

 originally a swamp, with the water 10 to 15 inches deep and filled 

 with the common swamp plants. In 1904 this was dredged to an 

 average depth of six feet to form an ornamental lake a hundred 

 yards broad and eight times as long. Two years after the building 

 of the lake there was a bloom with Anabaena spiroides predomi- 

 nating but accompanied by a small amount of Oscillatoria Agardhii. 

 In the latter part of 1908 0. Agardhii appeared in quantity and since 

 that time has always been found in great abundance during the late 

 months of the summer. Kolkowitz thinks that the great amount of 

 organic matter is the chief reason for the growth of Oscillatoria. 



Kolkowitz also discusses the flora of a number of artificial reser- 

 voirs in Germany that are 5 to 15 years old ('ii). In these the 

 Phaeophyceae and Volvocales are the most common organisms, blue- 

 green being present in some and lacking in others. 



In the Palisades Park the flora of the artificial Kanahwauke Lakes 

 and the artificially enlarged Stahahe and Cedar Lakes is character- 

 ized by a heavy growth of Myxophyceae. In the Kanahwauke 



