1920] Allen: Plankton of the San Joaquin River 65 



of the algae, that it was finally decided to give a list of totals of 

 algae (except Bacteriaceae) plus Mastigophora under the heading of 

 chlorophyll bearing organisms (tables 1-5). This plan was also fol- 

 lowed with the graphs in plates 3 to 6. A separate list of algae is 

 given under headings of Total Phytoplanktonts (text table 1, p. 31), 

 but no graph was made for it as the slight apparent difference did not 

 seem to warrant it. 



It will be noticed that this combination shows marked coherence 

 through the year. There is a rather prominent pulse in every month 

 through the first nine months at Stations I and II and in almost every 

 month at Station III. There is steady increase in numbers from May 

 to September at Stations II and III followed by a steady decline to 

 the end of the year, and at Station I the numbers were well maintained 

 from May to September with a steady decline following. The most 

 striking difference in the three stations concerns the maxima. The 

 maximum came in June at Station I and in September at the other 

 two. The June maximum at Station I was due, however, to the 

 enormous numbers of Cyclotella at that period. "With Cyclotella ex- 

 erting less influence on the totals or entirely omitted, the general 

 features of occurrence look much the same at Station I as at the other 

 two stations. 



The response to higher temperatures is quite noticeable at all sta- 

 tions, the larger numbers being especially characteristic of the time 

 from June to November when the temperature was usually near or 

 above 20° C. This, however, is also the time at which there was 

 least disturbance of the water. 



The recurrent pulses were very striking and may be conveniently 

 illustrated by Station II where the dates and intervals ran as fol- 

 lows: January 19, three weeks to February 8, three weeks to March 

 1, four weeks to March 29, three weeks to April 19, four weeks to 

 May 17, three weeks to June 7, three weeks to June 28, five weeks to 

 August 2, three weeks to August 23, two weeks to September 6, five 

 weeks to October 11, seven weeks to December 6. 



Fluctuations at Station II and III also showed a very close cor- 

 respondence with the volumetric record. This is probably because 

 the algae and Mastigophora furnished a large part of the volume at 

 those stations (plates 1, 4, 5). Such a conclusion is supported by 

 the fact that there is no such correspondence at Station I where the 

 Rotifera and Entomostraca furnish much of the volume (pi. 1, 3). 



