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 (PI. 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 us in 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 appareiit 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 



