0. H. Martin axd K. IJ. Lkwin 115 



From a consideration of cultural results alone, it would have been 

 imagined that flagellates, both large and small, and amoebae had been 

 the dominant forms. 



In a not very rich soil from a cauliflower seedling bed the picric 

 acid method gave a considerable variety of protozoa, no one form of 

 which appeared to have become predominant. It was fairly clear that 

 the density of the fauna was relatively low. It is interesting to observe 

 that this rather poor soil contained many more species than e.cj. the 

 soil from the cucumber border, though the latter had many more 

 individuals. This suggests an interesting analogy with results obtained 

 on the grass plots at Eothamsted, where the untreated (poor) plot 

 gives a large number of species, whereas on plots which have received 

 a large (piantity of manure for many years the number of species 

 is considerably curtailed. A similar phenomenon is shown in rich 

 infusions, in which as a rule at any given moment one or other protozoon 

 has got the upper hand, whilst in ordinary fresh-water pools the fauna 

 is far richer in number of species, but far poorer in number of individuals. 



The three Eothamsted field soils (Broadbalk dunged plot, Broadbalk 

 unmauured plot, and a fallow plot on Agdell) also contained protozoa 

 very sparsely, small amoebae being the most numerous, though thec- 

 amoebae were also represented. Flagellates were very rare, and ciliates 

 were not found at all in the active state. 



In culture, amoebae of the two types found in the cucumber border 

 were prominent, together with a great variety of flagellates and many 

 ciliates. The amoebae on the fresh films seem to be of a type different 

 from either the hmax or the lamelHpodian amoebae. 



Rather large amoebae of two sorts, both with a thick pellicle, were 

 obtained from the dunged plot on Broadbalk (14 tons farmyard manure 

 per acre each year since 1843) by the bubbling method. It is possible 

 that these were more resistant to a comparative degree of drought 

 than the more delicate types which flourished in the wet cucumber soil 

 and came on strongly in cultures from the field soil. 



By far the most abundant residts were obtained with samples of 

 these soils collected in November, 1913, when the moisture content of 

 the dunged plot was given by the usual method as 22 % . In the dry 

 summer of 1914 when the moisture on this plot varied usually between 

 13 % and 10 %, very poor results were given by all methods of investi- 

 gating the active fauna. There is a distinct probability that here the 

 water content is a limiting factor in determining the density of the 

 active fauna. 



8—2 



