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 Chlorophycee 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£. 
Actinastrum hanteschia 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 le in temper- 
atures above 65°. Asin 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 braunu Kitz..—Average number of colonies, 75. In 
previous years 1t 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 water- 
bloom, and is more abundant in the backwaters than in the main 
stream. 
Celastrum cambricum W. Archer.*—Average number of coeno- 
bia, 640,384 (silk, 477). Occurs from the latter part of March till 
