328 
“ June rise” set in, which culminated at 13.8 in the last week 
of May. The high levels, the rapid fall, and the subsequent rise 
are all associated with strong current and rapid replacement in 
channel waters. The early vernal rise in temperature noted 
in March did not continue with like rapidity. The rise from 
33° to 51° occurred in 21 days, while that from 49.5° to 73° 
takes 49 days. In 1898, 70° is attained on May 19, while in 1896 
it is reached 27 days earlier. The result of this delay in the 
vernal rise is seen in the shifting of the vernal maximum from 
April into May in 1898. 
The chemical conditions throughout this period are re- 
markably uniform. The great plankton wave of the 3d is ac- 
companied by but the slightest ripple in the nitrogenous matter 
in the stream, a slight drop in the nitrates and rise in the free 
ammonia being the only attendant phenomenon (Pl. XLV.). 
The average production in April, 4.4 cm.’ per m.*, is slightly 
below that of the two years preceding (5.67 and 5.11) as a result 
of the delay in the vernal rise and consequent shifting in the 
vernal maximum, and the May average (11.30) is for the same 
reasons much in excess of that in these earlier years (1.30 and 
5.62). 
The maximum of this vernal pulse (3 5.68 cm.*) is the lar- 
gest plankton content noted by usin channel waters. The con- 
ditions which environ this pulse are therefore of more than 
passing interest, since they must be potent factors in determin- 
ing production. Since the cyclic character of plankton produc- 
tion is apparent throughout the greater part of our records, we 
are not here concerned with those factors which operate to pro- 
duce this series of recurring waves of production, but only with 
those whose influence is potent in bringing about the unusual 
amplitude of this vernal pulse. 
In general we may group the important environing factors 
under the heads of chemical, thermal, and hydrographic condi- 
tions. From all that has been said in previous pages regarding 
chemical conditions it is not probable that they are immediate- - 
ly the occasion of this great development. An analysis of the 
