90 Vnivcrsitij of Califoniia Piiblirationa in Zoolomi T'^'f"- 22 



Ploima 



station I Station II Station III Daily Hourly 



Nuiiilior of forms rei-ordod 47 :i4 :i.i 27 29 



Iiiilivi.luals per cu. meter.. 4,491,499 799,224 1,215,618 5,322,812 5,4:!9,813 



I'loima were invariably present at all stations throughout the 

 year. The averages given above include the eggs, of which there were 

 about 30 per cent at Station I and Station III and over 40 per cent 

 at Station TI. Wliile the numbers were always rather largo they were 

 especially so in tciiiprratures above 15° C, the niaximum at Station 

 I occurring in June at a temperature of 22.5° C, in November at Sta- 

 tion II at 19.5° C, in November at Station III at 17° C. A marked 

 preference for sewage is proved by the exceedingly large numbers at 

 Station I, median numbers at Station III and smallest numbei's at 

 Station II. The large numbers in late summer and throughout the 

 autiuun at all stations also indicate a favorable effect of stagnation. 



The fact that all the Ploima show strikingly uniform character- 

 istics of seasonal distribution, noted by Kofoid (1908) in Illinois is 

 strongly in evidence here, especially amongst the forms occurring 

 throughout the year. Plates 3, 4 and 5 give a graphic representation 

 of the occurrence of the group as a whole (including eggs) accom- 

 panied by a similar graph for the chlorophyll bearers. This does not 

 indicate any prominent relationship of the two groups. The follow- 

 ing text table gives the more prominent pulses of Ploima at Station 

 I (exclusive of eggs). Omission or inclusion of eggs does not affect 

 the location of the pulses, hence eggs are not segi'cgated from other 

 records in totals at Stations II and III. 



Date No. Date No- Date No. 



Jan. 15 258,268 Jan. 29 567,996 Feb. 12 1,985,200 



Feb. 23 2,692,848 Mar. 12 .... 9,577,280 Apr. 5 5,.398,400 



Apr. 19 .. 6,526,912 Mav 11 9,936,352 June 3 4,.359,872 



June 25 .... 13,717,568 JulV 12 ... 5,979,752 July 26 4,649,952 



Aug. 20 .... 5,287,904 Sept. 13 .... 5,353,600 Oct. 8 7,105,.568 



Nov. 19 .... 802,848 Dec. 14 .... 723,508 



It may be seen that of the seventeen pulses noted in this table 

 eight preceded chlorophyll and algal pulses by from three to twelve 

 days, usually three or four days. Coincidence occurred twice, and 

 there were two cases in which ploiman pulses followed the others ])y a 

 few days. In the other five cases no definite relation appeared. It 

 therefore seems that there is no such clearness of relationshij) of 

 pulses of Ploima and of chlorophyll bearers as was noted in Illiiuiis 



