24 



Data for comparisons in the case of the more minute organisms 

 which escape the silk are lacking, since results of supplementary 

 methods have not, up to the present, been published elsewhere. 

 It seems probable, however, that the Chlorophycecs will be found to 

 be somewhat more characteristic of the plankton of rivers than of 

 lakes, and to be more prevalent wherever the shore with its decay- 

 ing vegetation forms a large factor in the environment or where 

 sewage contamination affords the requisite food for their develop- 

 ment. 



DISCUSSION OF SPECIES OF CHLOROPHYCE^E. 



Actinastrum hantzschii Lagerh.* Average number, 199,038 

 (silk net, 338). From May until the middle of November, with 

 maximum of 21,600,000 on August 30, 1898, and of 122,000,000 on 

 September 21, 1897. There are also indications of a vernal pulse, 

 which on May 25, 1897, attained 90,000,000. The major pulse 

 occurs late in the summer, in August and September, while dimin- 

 ished numbers continue until the first of November. Three single 

 occurrences were noted in January, 1898, following the unusual 

 prevalence of 1897, but aside from these the species occurs in the 

 plankton at temperatures above 45, and both pulses lie in temper- 

 atures above 65. As in many other species, a greater development 

 was attained in 1897, in stable low water, than in 1898 in disturbed 

 hydrographic conditions. This species occurs in the water-bloom, is 

 favored by stable conditions, and finds its optimum temperature 

 between 65 and 80. 



Botryococcus braunii Kiitz. Average number of colonies, 75. In 

 previous years it was much more abundant, averaging 3,300 in 1897. 

 It occurs from the first of April well into October, though in 1897 it 

 continued until the middle of December. It may thus appear 

 throughout the whole range of temperatures, 32 to 90, but as a 

 rule occurs above 60. There is a suggestion of a minor pulse in 

 June, 1896, but not in other years. The major pulse attains 

 57,200 on August 15, 1896, and 42,000 on September 14, 1897, and 

 appears, with smaller numbers, in August of preceding years. The 

 species occurred but sparingly in 1898. It is found in the w T ater- 

 bloom, and is more abundant in the backwaters than in the main 

 stream. 



Ccelastrum cambricum W. Archer.* Average number of cceno- 

 bia, 640,384 (silk, 477). Occurs from the latter part of March till 



