ABSTRACTS 679 



power in the soil complex. The addition of manure materially raises 

 the oxidizing power, especially under continuous wheat and corn. The 

 addition of commercial fertilizer brings about a condition similar to 

 that of manure, though perhaps less marked." — H. J. C. 



Studies on the Activity of Soil Protozoa. G. P. Koch. Soil Science, 



1916, 2, 163-181. 



The approximate time for protozoa to excyst when the cysts come 

 in contact with free water was determined to be five to seven minutes. 



Data are given in regard to the influence of moisture content, physi- 

 cal character of the soil and the presence of organic matter upon the 

 activity of protozoa in the soil. About 0.33 gm. of soil was taken for 

 daily examination for active protozoa. The type of soil determines 

 whether the addition of organic matter encourages protozoan devel- 

 opment. It was indicated that the destructive abihty of soil protozoa 

 (if they possess this power) would be present only for a limited period, 

 namely, in the early stages of organic decomposition. Increasing the 

 porosity and aeration of the soils by the addition of sand did not in- 

 crease the number of motile protozoa. 



With the soils used, moisture seemed to be the primary limiting factor 

 which determined the presence or absence of active protozoa. 



With one exception, no correlation between the presence of proto- 

 zoa in the active condition and numbers of bacteria could be seen. 

 Increased numbers of bacteria were observed irrespective of the pres- 

 ence or absence of living protozoa. Inasmuch as the numbers of pro- 

 tozoa in comparison with the bacterial numbers are so small, even in 

 the presence of such abnormal quantities of organic matter as were 

 used in these experiments, it hardly seems that they would be of very 

 great importance in agricultural practice. — Z. N. 



Soil Fungi and their Activities. S. A. Waksman. Soil Science, 1916 



2, 103-156. 



The author has endeavored in this paper to ascertain: (1) What 

 fungi are true soil organisms, i.e., occur continually and in most soils; 

 (2) The part that these organisms play in the fertility of the soil. 



The micro-flora of eight soils from various portions of the United 

 States was studied, from which were isolated nineteen species belong- 

 ing to the Phycomycetes, several to the Ascomycetes, including uni- 

 dentified species of yeasts, and eighty species to the Fungi Imperfecti, 

 all of which were included in thirty-one genera. The most common 

 genera of fungi as to numbers and species found in the soils investi- 

 gated are, in the order of their occurrence, as follows: Penicillium, 

 Mucor, Aspergillus, Irichoderma, Cladosporium, Fusarium, Cephalo- 

 sporium, Rhizopus, Zygorhynchus, Acrostalagmus, Alternaria and 

 Verticillium. A hypothetical soil flora is given. 



Physiological studies were made of types representative of fungus 

 groups with regard to their nitrogen-fixing and anmionifying power, 



