274 
Ranceua Total Average height, | Average number 
Year ee movement, | in ft., of stage of znsectus 
levels, in ft. : : 
in ft. of river per m.3 
NSO SEM eect erat WAR) 5149 3.61 2,966 
1896 Ge ave ieee en pek iQ). 1 AVS 7 6.98 949 
NBO eaten 5 Ap 14.3 44.8 6.90 Delete 
Ione guctain Sicko LS) 5 Of. 8.02 539 
then, of lowest levels, least range, and total movement, we find the 
largest development (2,966) of amsectus 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 zmsectus falls 
to 949 per m.* In 1897 the population rises to 2,115 per m.°, 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.* 
A detailed comparison of the July-November period of the two 
years follows. 
Mioumthesyaisera sveuceeae eee July August September 
WiG Bias Basacde Aimreuekcher hake eee 1897 1898 1897 1898 1897 1898 
Total movement....... oe 7.4 2.6 je 0.6 6.2 
SANETAGC SLALE... sae ass 6.05 D0 2.29 3.66 |. 2:01 4.44 
| 
Average number of C. 
viridis var. insectus...| 5,093 210 2 ,030 304 2a2o 325 
