70 



crease of Bicosceca in the plankton, but is not in itself the primary 

 cause for its appearance in the plankton. 



Carteria multifilis (Fres.) Dill.* Average number, 2,365,384. 

 In 1897 more than one hundred -fold as abundant. This species was 

 recognized only in the autumnal and hiemal planktons, from 

 August till January in 1897-98 and from October to February in 

 1898-99. It is not easily and with certainty identified by the 

 usual methods of plankton counting, and probably other species of 

 similar habitus may have been included to some extent ; and, on the 

 other hand, many Carteria may have been thrown with the "un- 

 identified" flagellates, especially in earlier years. This species 

 occurs throughout the whole range of temperatures, and its maxi- 

 mum development (6,476,400,000) was attained October 5, 1897, at 

 70. A pulse prior to this appeared September 7, at 2,846,250,000. 

 From the major pulse in October there is a gradual decline as the 

 minimum temperatures are reached. 



The remarkable outbreak of Carteria in the autumn of 1897 was 

 associated with unusually low water (Pt. I., PI. XI.) and concen- 

 tration of sewage and decrease in current. The water of the stream 

 was of a livid greenish-yellow tinge, due principally to great numbers 

 of Carteria, which developed to the exclusion or diminution of other 

 chlorophyll-bearing flagellates such as Euglena, and of diatoms such 

 as Melosira. This unusual development seems to have been a dis- 

 turbing factor in the usual seasonal routine of the autumnal plank- 

 ton of that year. 



The distribution of Carteria in the river was remarkable. It 

 formed great bands or streaks visible near the surface, or masses 

 which in form simulated cloud effects. The distribution was 

 plainly uneven, giving a banded or mottled appearance to the 

 stream. The bands, 10 to 50 meters in width, ran with the channel 

 or current, and their position and form were plainly influenced by 

 these factors. No cause was apparent for the mottled regions. 

 This phenomenon stands in somewhat sharp contrast to the distri- 

 bution of the usual water-bloom upon the river, which is generally 

 composed largely of Euglena. This presents a much more uniform 

 distribution, and unlike the Carteria is plainly visible only when it 

 is accumulated as a superficial scum or film. Carteria was present 

 in such quantity that its distribution was evident at lower levels 

 so far as the turbidity would permit it to be seen. It afforded a 



