11 



DAILY PERIODICITY IN THE NUMBERS OF ACTIVE 



SOIL FLAGELLATES: WITH A BRIEF NOTE ON 



THE RELATION OF TROPHIC AMOEBAE AND 



BACTERIAL NUMBERS. 



By D. WARD CUTLER and L. M. CRUMP. 



(Rothamsted Experimental Station.) 



(1 Map and 7 text-figs.) 



In a recent paper by one of us (4) are given the results of periodical 

 counts of the protozoa found in certain of the Rothamsted fields. 

 These numbers refer, however, to the total protozoan population irre- 

 spective of their physiological conditions — cystic or trophic. A method (6) 

 has recently been devised by which these two states can be separated 

 and the numbers counted. From October 8th, 1919 to January 29th, 

 1920 fortnightly soil samples were taken from the dunged plot of 

 Rothamsted wheat field and the trophic and cystic protozoa counted. 



Fig. 1 gives the active numbers per gr. of soil for three species of 

 flagellates (Oicomonas sp. (Martin), Cercomonas longicauda, Bodo sp.), the 

 numbers of trophic amoebae and the bacterial numbers. On the same 

 curve is also given the moisture content of the soil. Fig. 2 shows the 

 curves for the daily rainfall and soil temperature 1 ft. depth (Meteoro- 

 logical Office type thermometer) during the period. 



Examination of these curves suggests no correlation between the 

 number of active organisms and the temperature or water content, but 

 there is an indication of periodicity in the fluctuations of numbers of 

 active flagellates. The sudden rise in numbers on Nov. 13th is probably 

 due to addition of manure to the soil seven days previously. It is inter- 

 esting to note, however, that this did not prevent cyst formation and 

 subsequent reduction in active numbers on Nov. 25th. 



As the soil samples were taken at approximately fortnightly intervals 

 the figures give no information as to the daily fluctuations in number 

 of the protozoa — obviously a matter of great interest; to determine this 

 daily samples were taken from the Broadbalk dunged plot — the first 

 on Feb. 9th, 1920. 



