486 



Journal of Agricultural Research 



Vol. V. No. II 



during the 2-minute examination, for in no case were any living protozoa 

 found. It was later found with a limited number of soils examined that 

 no protozoa were observed to excyst in a 5- or even 7-minute period. 

 More evidence on this point is being collected. 



Some evidence as to the length of time required for the excystment 

 of soil protozoa when sufficient moisture is available is presented in Tables 

 II and IV. As shown in Table IV, at the incubation temperatures of 

 5° to 7° and 32° to 33° a few small ciliates and flagellates were observed 

 8 hours after the increased additions of water were made to the soils. 

 It is also seen that in nearly all samples incubated at 15° to 17°, 22° to 

 24°, 32° to 33°, and at outdoor temperatures some motile protozoa were 

 present after 30 hours. The higher temperatures seemed to be more 

 favorable for the more rapid excystment. This was also found to be 

 true (i) when protozoa were developed in artificial-culture solutions. 

 Small ciliates excysted in as short a period as did the flagellates. In 

 Table II it is shown that after the soils had been in contact with water 

 for 40 hours all of them showed the presence of small ciliates and flagel- 

 lates. In several samples active large ciliates were also observed. 



In order to accumulate more data as to the period of excystment of 

 protozoa a small sample of each of the three soils (samples air-dried and 

 samples containing an optimum amount of moisture and incubated at 

 22° to 24°, as given in Table III and in the text just following Table III) 

 were added to a few drops of sterile tap water on a glass slide with a large 

 depression in the center. The soil was stirred with a stirring rod and the 

 film spread over the surface of the slide. A careful examination of each 

 sample was made for a period of five minutes, and the slides containing 

 the samples were then placed in the incubator. They were again exam- 

 ined for 5-minute periods at intervals of 15 minutes and i, 2, 3, 5, 6, 

 and 8 hours. (See Table VI.) 



Table VI. — Time required for the excystment of soil protozoa at 22° to 24° C. 



S. C.t= few small ciliates; F.t=few flagellates; F.tt=several flagellates. 



From the data recorded in Table VI it will be noted that at 22° to 24° 

 protozoa (small ciliates) may excyst within two hours after the protective 

 cysts come in contact with available moisture. Flagellates and other 



