191G] AGRICULTURAL BOTANY. 525 



and for this reason they have been considered important ammonifiers of the 

 soil. A series of tests was conducted to determine the significance of these 

 organisms in the soil, 26 tests being made to ascertain tlieir relative importance 

 in heated and unheated soil infusions. 



Wiien the soil infusion was heated before plating to a temperature of from 

 75 to 85° C, nearly, if not quite, as many colonies of these bacteria developed 

 as when plated from unheated infusions. This temperature is considered high 

 enough to kill the vegetative forms of bacteria, and I heir constant occurrence 

 in large number is believed to suggest that the bacteria are present in normal 

 soils as spores rather than in the vegetative state. No increase in the total 

 number of these organisms and no decrease in the number of their spores could 

 be detected in soil to which fresh manure was added. These results are con- 

 sidered as casting doubt on the common assumption that these organisms are 

 important ammonifiers in the soil and they raise a question as to what pos- 

 sible soil conditions favor their growth and multiplication. 



A possible function of Actinomycetes in soil, H. J. Conn (New York State 

 .S7a. Tech. Bui. 52 {1916), pp. 3-11).— In the course of a qualltativ(> study of 

 the bacteria in certain New York State soils, there was recognized a great 

 similarity between the different soils and the relative numbers of Actinomy- 

 cetes and lower bacteria present, provided the soils were in the same state of 

 cultivation. Later it was found that Actinomycetes were practically always 

 present in greater abundance in old sod soil than in soil recently cultivated. 

 An investigation of this subject has shown that the average ratio between the 

 number of Actinomycetes in neighboring sod and cultivated spots of ihe same 

 soil type is slightly more than 2:1. In a study of three neighborir.g spots in a 

 single soil type, it was found that Actinomycetes colonies not only appeared 

 in greater numbers from sod than from cultivated soil but also appeared in 

 greater numbers from old sod than from sod only two or three years old. The 

 reason for this difference in numbers has not been learned, but it is suggested 

 that Actinomycetes are active in the decomposition of grass roots. 



The number of colonies allowable on satisfactory agar plates, R. S. Breed 

 and W. D. Dottereeu {New York State Sta. Tech. Bui. 53 {1916), pp. 3-11).— 

 Attention is called to the importance in making bacteriological counts of the 

 limit in the number of colonies that may be allowed to grow on a plate with- 

 out introducing serious errors, and the authors present the results of an in- 

 vestigation testing the standard methods for bacterial milk analysis as adopted 

 by the American Public Health Association and as modified in its meetmg of 

 1915 (E. S. R., 35, p. 70). 



The work reported includes a study of the counts made for a large number 

 of agar plates incubated for five days at 21° C, and of some of the same plates 

 after tv>^o days' additional incubation at 37°. The results obtained indicate 

 that for milk analysis counts made from plates having more than 30 and less 

 than 400 colonies are very nearly as satisfactory as those made from plates 

 having more than 40 and less than 200 colonies. 



A comparison between agar and gelatin as media for the plate method of 

 counting bacteria, H. J. Conn and W. D. Dotterrek {New York State Sta. 

 Tech. Bui. 53 {1916), pp. 12-15). — A comparison has been made between the 

 counts obtained from G41 agar plates and 599 gelatin plates inoculated v.-ith 

 various samples of soil, and the results show that the discrepant counts are as 

 likely to occur with one medium as with the other. The remarkable agreement 

 between the two media is believed to indicate that the nature of the medium 

 used has little or no influence in producing the occasional widely discrepant 

 counts which occur. 



63270°— No. 6—16 3 



