274 



then, of lowest levels, least range, and total movement, we find the 

 largest development (2,966) of insectus in channel plankton. 



In 1896 the average river level is much higher, affording in- 

 creased current and more silt. A series of recurrent floods also 

 flush the channel, though the total movement and range in levels 

 within the limits of the year are not greatly increased. Neverthe- 

 less, the changes, which appear mainly below bank-height, affect 

 channel plankton profoundly, and the production of insectus falls 

 to 949 per m. 3 In 1897 the population rises to 2,115 per m. 3 , largely 

 as a result of the stable conditions of flood-free waters at low levels 

 and with slight current in the last half of the year. In 1898 the 

 total movement (67.2), range in levels (15.5), and average stage 

 (8.02) reach the extremes in the four years under comparison, and 

 the insectus population falls to the lowest level 539 per m. 3 



A detailed comparison of the July-November period of the two 

 years follows. 



