1920] Allen: Plankton of the San Joaquin River 117 



3. The two pulses of chlorophyll bearers were closely accompanied 

 by similar pulses of Protozoa (exclusive of Mastigophora) and of 

 Rotifera. 



4. It is very necessary to have similar series covering several lunar 

 cycles in order to evaluate the various factors of distribution and the 

 bonds of relationship of plankton organisms. 



Before leaving the discussion of this series, the point should be 

 emphasized that daily collections frequently give a very different view 

 of the situation from any that may be obtained at longer intervals. 

 Comparison of plates 3 and 1 (graph Station I and Daily) shows this 

 very clearly. Referring first to plate 1, it will be seen that although 

 the regular Station I series was taken twice a week the difference is 

 very great. In the Station I regular series the volumetric maximum 

 came on July 30, but the daily record shows that four catches (July 

 13, 18, 20, and 27) exceeded it, two of them greatly. The semiweekly 

 record shows this maximum on the rise of a pulse while the daily 

 record shows it as on the decline of another. The daily record also 

 shows marked fluctuations in volume of the catches during this lunar 

 cycle which are not indicated by the other. 



If the regular series had been taken only once a week (which is 

 usually the shortest interval used by investigators), the dates would 

 have been July 5, 12, 19, 26, and August 2. Comparing this with the 

 daily record we see that it would have shown an erroneous picture 

 of conditions since it would have indicated a considerable abrupt rise 

 in volumes to fairly stable, higher levels. 



Turning to plates 3 and 6, we find the same tilings true. In the 

 case of the Entomostraca the remarkable pulse from July 20 to 23 i.s 

 entirely missed by even the semiweekly method. While the pulses of 

 the other groups are not entirely missed, they appear much more ab- 

 rupt in the regular series than they really are. 



In consequence of these remarkable differences it is surely clear 

 that only the most general conclusions may be safely drawn from 

 series of catches taken at intervals greater than one day. 



THE HOURLY SERIES 



This series, covering a period of about twelve hours on August 11, 

 was undertaken in the hope of finding some indication of the import- 

 ance of the daily tidal currents in a study of the plankton. It was 



