542 Journal of Agricultural Research voi.iv, no.6 



observed to be present throughout the experiment. Similar protozoa 

 appeared on the fourteenth day in hay infusion to which greenhouse soil 

 had been added. 



In hay infusion it was very apparent that as the numbers of protozoa 

 decreased the number of cysts increased. That all the protozoa do not 

 encyst when conditions become unfavorable is shown by the fact that 

 very many dead forms of Glaucoma and Prorodon were seen. 



On the twentieth day species of Euglena appeared in dried blood inoc- 

 ulated with field soil and in hay infusion to which greenhouse soil had been 

 added. The latter solution was favorable for the development of these 

 organisms, as 600 per gram of soil appeared on the twentieth day, while 

 on the thirtieth day 28,000 organisms of Euglena spp. per gram were 

 counted. 



That the soils examined contained a small number of amoebae cysts 

 or that the conditions in the culture solutions were unfavorable for their 

 development was judged by the fact that very few were observ^ed. From 

 the soil inoculations in dried blood no fonns of amccbae were recognized, 

 while in the case of the hay infusion to which greenhouse soil had been 

 added a few were observed on the twenty-first day. 



SUMMARY OF P.^RT III 



Under the conditions of this experiment and of Part II it is apparent 

 that in developing protozoa from the soil in artificial culture solutions 

 different numbers and types of protozoa will be developed for every 

 variation in the amounts of each soil used for inoculation and with every 

 culture solution used. 



IV.— EFFECT OF TEMPERATURE UPON THE DEVELOPMENT OF SOIL 



PROTOZOA 



INTRODUCTIOX 



In the earlier experiments recorded in Parts II and III of this article 

 it was shown that the development of the numbers and types of soil 

 protozoa in artificial culture solutions varied with the kind of culture 

 solutions as well as with the quantity, physical condition, and kind of 

 soil used for inoculation. 



The problem under discussion deals with the development of the 

 numbers and types of soil protozoa which appear at various tempera- 

 tures in artificial culture solutions inoculated with soil of different origin. 



That different conditions of temperature affect the development of 

 protozoa in the soil was recorded by Cunningham (3, p. 14), who, after 

 inoculating a quantity of soil for a period of nine days at 5 to 7° C, then 

 increasing the incubation temperature to 22° C, noted an increase in 

 the numbers of protozoa developed after seven days. "Exposure to a 

 temperature of 30° C. for seven days has caused a fall in the total num- 

 bers but a distinct rise in the number of cysts." 



