AGRICULTURAL BOTANY. 227 



vital activities, the blocliemicul factors being especially prominent. Numerous 

 bodies which occur in soils arise either in the metabolic activities of micro- 

 organisms or are left there after the decomposition of the plant and animal 

 d6bris, and probably also as a result of root excretion or cell sloughing. Some 

 of these substances are harmful, and others beneficial to crops. Fertilizers 

 tend to modify the physiological functions of the micro-organisms by bringing 

 about suitable conditions for their development, by stimulating or retarding 

 their digestion of inert bodies, and by furthering their enzymotic functions. 



Bacteria of frozen soil, H. J. Conn (.16.s. in Science, n. ser., 33 {1911), No. 

 849, p. 543). — The author briefly summarizes the results of investigations on 

 this subject carried on at Ithaca, N. Y., during 1909-10, which showed a re- 

 markable increase in soil bacteria during the winter, the increase being from 

 7,000,000 per gram in November, 1909, to 33.000.000 in February, 1910, and 

 from 8,000,000 in November. 1910. to 22,000.000 in December, 1910. The quan- 

 titative results have been previously rei)orted (E. S. R., 24, p. 529), while the 

 qualitative work, including the study of some .300 cultures, is here discussed. 



It was found that certain organisms were present throughout the year, while 

 others appeared only at times and showed a tendency to reappear at the same 

 seasons another year, fall and winter showing the greatest diversity of types. 

 Four groups of bacteria were studied, as follows: (1) Higher filamentous bac- 

 teria (Actinomyces) ; (2) rapid liquefiers producing spores, mostly of the 

 Bacillus fiuhtilis group; (3) rapid liquotiers without sj)ores, all but one being 

 Pseudomonas forms; (4) slow growers without spores, producing punctiform 

 colonies, partly liquefiers and partly nonliquefiers. This last group is the one 

 containing the bacteria which increase the most noticeably in the winter. 



On methods of measuring the bacterial activity of cultivated soils', R. 

 Perotti (Atti R. Aecad. Lincei, Rend. CI. Set. Fis., Mat. e IVat., 5. ser., 20 

 (1911), 7, No. J,, pp. 266-21.',, fig. i).— The author briefly reviews the methods 

 of prominent investigators, especially Remy's. for determining ammonification, 

 nitrification, dcnitrifieation, aiid nitrogen fixation in different soils, and con- 

 cludes that Remy's methods as used by Barthel (E. S. R., 21, p. 528) for the 

 study of soil bacteriology are probably the best. 



Attention is called to the results obtained in measuring ammonification, 

 nitrification, and dentrification in certain Italian soils (E. S. R., 24, p. 717), 

 in which there was a marked difference between ammonification and nitrifica- 

 tion produced by certain of these soils during the winter and summer seasons, 

 being much greater during the month of February than in July. These experi- 

 ments also showed a greater degree of nitrification for soils having 10.5 per 

 cent of organic matter than soils containing only 8.8 per cent. 



Studies in soil bacteriology. — II, Ammonification in soils and in solutions, 

 F. L. Stevens, W. A. Withers, et al. {North Carolina Sta. Rpt. 1909, pp. 119- 

 12S). — Previously noted from another source (E. S. R., 21, p. 619). 



Studies in soil bacteriology. — III, Concerning methods for determination 

 of nitrifying and ammonifying powers of soils, F. L. Stevens and W. A. 

 Withers {North Carolina Sta. Rpt. 1909, pp. 129-144, dgms. 4). — Previously 

 noted from another source (E. S. R.. 22, p. 427). 



Bacteriological studies of the soils of the Truckee-Carson irrigation 

 project [Fallon, Nev.], K. F. Kellerman and E. R. Axlen {U. S. Dept. Agr., 

 Bur. Plant Indus. Bui. 211, pp. 36, figs. 20). — The results are given of experi- 

 ments on the nitrifying and ammonifying power of soils at different depths, 

 on the nitrification of samples in solution, on the relation of chlorids and sul- 

 phates to nitrification, and on denitrification. The relative number of bacteria 

 in different soils were estimated, and detailed studies of soils typical of ex- 

 tensive areas reported. All studies were made of a 3-foot zone, keeping sepa- 



