19171 AGRICULTURAL BOTANY. 221 



The development of Azotobacter, A. Cauda {Sta::. Sper. Agr. Ital., 40 {1916), 

 No. 2, pp. 125-lSl). — Details are given of a study during several years of 

 Azotobacter, as regards its morphology, its relationships, and its physiology as 

 influenced by salts of phosphoric acid, by calcium carbonate, by magnesium and 

 nitrogen compounds, by humus and various other soils, and by association with 

 other organisms. 



The soils which are rich, well worked, and provided with humus and mineral 

 fertilizers, prove to be those in which the development of Azotobacter is most 

 active. This fact agrees with the observed results obtained from practice on 

 well-managed farms. 



The oxygen requirements of biological soil processes, T. J. Muebay {Jour. 

 Bad., 1 {1916), No. 6, pp. 597-614).— In the work here detailed, which was 

 planned to test the relative influence of aerobic and anaerobic conditions on 

 some fundamental processes due to the agency of soil bacteria, the author found 

 that denitrification goes on under aerobic and anaerobic conditions, being little 

 affected by either. Denitrification proceeds better in solutions than in soils, 

 nitrogen being lost in the greenhouse type of soil used but not in either a 

 Bilt loam or a day hillside soil. 



Depression of the freezing point in triturated plant tissues and the magni- 

 tude of this depression as related to soil moisture, R. P. Hibbard and O. E. 

 Harrington {Physiol. Researches, 1 {1916), No. 10, pp. 441-458). — This paper 

 deals with the freezing-point lowering that characterizes the pulpy mass formed 

 by grinding plant tissues, and presents evidence that this lowering is as valu- 

 rtble a criterion for comparing osmotic concentrations of the tissues as is the 

 corresponding index for the expressed juice. The material was first subjected 

 to a preliminary freezing, to render the cell membranes more readily permeable 

 to dissolved materials, after which it was thoroughly triturated. The pulp 

 thus prepared was placed in the cryoscopic apparatus and its freezing-point de- 

 pression determined just as is usually done with the sap expressed from such 

 pulps. Beckmann's freezing point apparatus was employed. 



It was found that this method of testing the pulp without pressing gave 

 concordant results when different samples of the same pulp were tested. In a 

 series of duplicate tests the greatest plus or minus variation between two 

 lowerings that one might expect to be alike was only 0.5 per cent ; usually it 

 was less than this. Comparisons of the depressions obtained from tests of 

 plant pulps with those from tests of the expressed juices of the same pulps 

 showed that the two values obtained in these two ways were practically iden- 

 tical, providing that the process of pressing had been very thorough. The agree- 

 ment was usually within much less than 1 per cent. 



The materials employed in these tests were potato tubers, cabbage leaves 

 (from the head), apples, lemons, oranges, grapefruit, onion bulbs, and the tops 

 and roots of maize plants grown in pot cultures. In the case of the maize 

 plants the pots were furnished with autoirrigators, so arranged that six dif- 

 ferent degrees of soil moisture were practically maintained, in as many dif- 

 ferent cultures. It was found that the triturated tops showed depressions of 

 from 1.835° C. (culture with mean soil moisture of 31 per cent on dry weight) 

 to 2.204° (culture with soil moisture of 11 per cent), and that the ground roots 

 showed corresponding depressions of from 0.492 to 0.995°. The root material 

 thus had a much lower depression (and consequently a much lower osmotic 

 concentration) than the top material. The depression of the freezing point was 

 found to increase, for both tops and roots, as the moisture content of the soil 

 in which the plants grew decreased, from culture to culture in the series. The 

 order of magnitudes was the same for both roots and tops, being the reverse 

 of the order for soil moisture content. 



