307 
exceed, if indeed equal, that of years of more normal hydro- 
raph. 
ae 1896. 
(Tables III, X.; Pl. X., LL) 
There were 76 collections made in this year, of which 69 
are prior to Sept. land are, moreover, at intervals brief enough 
to enable us to trace the curve of plankton production with 
some degree of accuracy. In the last four months the fort- 
nightly interval is too great to permit more than conjecture as 
to the probable course of the plankton curve. 
The collections prior to May 22 were all the result of com- 
bining 4 to 9 repeated vertical hauls of the net. Subsequent to 
that date they were made with the plankton pump. This, as is 
shown on page 165, was a year marked by recurrent floods, 
which bring the average height for the year up to 6.98 ft. ina 
year of less than average rainfall. This is almost twice the 
average height (3.61) of the preceding year. Since the flood 
did not in most cases reach bank height, the overflows were 
not extensive and did not occur during periods of large plank- 
ton production (Pl. X.). The distribution of the collections 
with reference to the floods is such that we have again in this 
year the opportunity to test the effect of the access of flood wa- 
ter upon the curve of plankton production at all seasons of the 
year but the autumn months. Inthis year the vernal rise in 
temperature occurred abruptly in the middle of April, and 
the autumn decline began quite early but progressed slowly. 
Summer temperatures were also lowered somewhat by access 
of flood water. 
The plankton of January, February, and March (P\. X.) 
forms so small a portion of the total catches that its quantita- 
tive changes are swamped by the probable error of silt estima- 
tion, and are apparently of such slight extent that their signifi- 
cance cannot be detected. The amount of silt carried is very 
large, doubling or trebling in quantity on rising floods, and 
reaching a maximum of 14.77 em.’ per m.* on the crest of the 
March freshet. Norecurrent pulses appear in the volumetric 
