118 University of California Publications in Zoology [ VoL - 22 



also expected that some information might be obtained as to diurnal 

 influences of light. The series is too short to be satisfactory (twenty- 

 four hours would be better) and several days should be covered in- 

 stead of one. 



Despite these defects, the records indicate some points of interest. 

 It happened that on the day selected low tide came at about 11 a.m. 

 at Stockton, but there was no available way of recording the tide 

 accurately. There is nothing in the record that can be positively 

 connected with tides. 



Still less than in the Daily series does there seem to be anything 

 indicated by the species record which is not as well shown by major 

 groups. For that reason the general discussion only will be given. 

 Reference to table 5 will easily show such detail as has been recorded. 



Since chlorophyll bearing organisms give, to a large extent, the 

 basis of interpretation of plankton conditions they may receive first 

 attention. Plate 6 (hourly) shows a preliminary drop in numbers 

 from 7 a.m. to 8 a.m. a nearly uniform succession of catches to 12 m. 

 and a constant rise through the remainder of the series to the close 

 at 6 :45 p.m. A graph of such very prominent characters demands 

 explanation, but the demand cannot be fully satisfied from the present 

 records. During the forenoon period of nearly uniform numbers the 

 tide was ebbing, the air was hazy with full sunlight, there was little 

 wind and the water was nearly smooth most of the time. In the 

 afternoon period of rapidly and constantly rising numbers there was 

 flowing tide, hazy air with full sunlight, strong wind, almost a gale 

 at the close, and very rough water, with strong cross currents due 

 to wind. The water temperature varied from 24° C at 7 a.m. to 26° C 

 from 11 a.m. to 4 p.m. and to 25° C at 6:45 p.m. Among the observ- 

 able factors involved, the temperature seemed to be the only one of 

 sufficient constancy to account for the increase. Light was the only 

 other factor that seemed likely to have had a beneficial effect and it 

 was surely very much poorer in the afternoon on account of rough 

 water. In view of such adverse conditions as rough water and poorer 

 light it would have been reasonable to expect that there would at 

 .least be no increase in numbers of plankton in the afternoon. As 

 the evidence stands it points distinctly to the conclusion that temper- 

 ature was the dominant factor in the diurnal fluctuation of chlorophyll 

 bearers. 



If there had been only one or two larger catches in the afternoon 

 or if there had been fluctuation in numbers there might be some 



