


Die 
Ree Total Average height, | Average number 
Year 1 Seo o movement, in ft., of stage of znsectus 
Bees oat in 6, of river Perens 
18905. ss. 22: nee {2 51.9 3.61 2,966 
(SOG, Ric Sane 10.1 45.7 6.98 949 
OOS Ars oe 14.3 44.8 6.90 A ANAS) 
1SOSR aac eee 155 Ovnae 8.02 539 





then, of lowest levels, least range, and total movement, we find the 
largest development (2,966) of zmsectus 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 znsectus 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 znsectus population falls to the lowest level—539 per m.3 
A detailed comparison of the July—November period of the two 
years follows. 










Mont tai oc.eete etree July August | September 
MiGaieenctch oe Soret | 1897 1898 1897 1898 | 1897 1898 
Total movement....... |e! 7.4 2.6 Los NW Os On 
Average stage......:.. 6.05 By (AO) = Bao) 3.66 2aOn 4.44 
Average number of C. 
viridis var. insectus...| 5,093 210 2,030 304 2 Dis 325 
| | 
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