BOILS — FERTILIZERS. 121 



scopicity and the colloidal material of tlie soil iu relation to the plijsics and 

 C'lieniistiy of plant growth is discussed. 



The drying of soils, G. A. Ritter (CcitthL Balct. [etc.}, 2. Aht., 33 (1912), 

 A'o, 1-6, pp. Il6-l'i3). — Studies are reported of the bacterial activity of wet and 

 of dried soils as measured by the formation of acid and of carbon dioxid iu 

 culture solutions, as affected by the physical and chemical properties of the soil, 

 the character of the culture metlium, the kind of vegetation, alternate drying 

 and wetting, rate and degree of drying, and temperature. The Remy method 

 cr a modification of it was used. 



There was found to be a difference in the bacterial activity of the dry as 

 compared with that of the wet soils, the dry soils causing a quicker and more 

 intense fermentation. These differences were most marked at the beginning of 

 fermentation but later tended to disappear. The time of reaching the maximum 

 formation of acid varied for the different soils, but always was shortest for the 

 dry soils. The maxima of acid formation varied with the different kinds of soil 

 as well as with the water contenl; of a given soil, although the latter variation, 

 excepting in a wet and heavy clay soil, was for the most part unimportant and 

 often fell within the limits of experimental error. The calcium carbonate con- 

 tent of the soils also influenced somewhat the formation of acid, but the viru- 

 lence of the bacteria as determined by the physical and chemical properties of 

 the soil was the determining factor. It is held that the extent of variation in 

 the physiological relations in wet and in dry samples of the same soil is deter- 

 mined by or is a function of tlie bacterial activity of the soil. 



The author asserts that the Romy method of bacteriological soil investigations 

 is correct in principle. He urges that attention be given to the elimination of 

 variable factors which may vitiate the results, such as variable water content of 

 the soil, careless methods of preserving soil samples, and variations in tempera- 

 ture and light. 



The oxyg'en content of soil water and its influence on the swamping of 

 the soil and the growth of forests, A. H. Hesselman {Meddel. Stat. Slcogs- 

 forsoksanst. (Mitt. Forstl. Vers. Anst. Schwedens), 1910, No. 7, pp. 91-125+ 

 XIII-XVI, figs. 5). — Studies of the oxygen content in surface and subsoil 

 waters of forest swamps and of the absorption of oxygen from water by dif- 

 ferent forest molds and soils are reported with a view of determining the cause 

 of the swamping of pine forests in northern Sweden. 



The results, in general, showed that where there was sufficient movement the 

 water was well supplied with oxygen. The water of the moors of swamped 

 pine forests contained no oxygen at a depth of 20 cm. Near the surface it con- 

 tained traces of oxygen. Sphagnum layers reduced the oxygen content of the 

 water. The absorption of oxygen was much less for beech forest than for pine 

 forest soils and for sterilized neutral than for unsterilized soils, and less for the 

 humus of a rapidly growing pine forest than for that of a swamping forest. 



The general conclusion drawn from these studies is that the swamping of 

 forest soils of Sweden is not due to overabundance of water but to its low 

 oxygen content. In some places, where the water was in motion and thus 

 aerated, pine forests made a very vigorous growth even where the soil was 

 covered with water. 



Evaporation from irrigated soils, S. Fortier and S. H. Beckett (f7. 8. 

 Dept. Agr., Office Expt. Bias. Bui. 2-'i8, pp. 77, pis. 2, figs. 27).— This bulletin 

 reports a continuation of experim-ents reported upon in a previous bulletin 

 (E. S. R., 18, p. 1087), extending the observations to colder and more elevated 

 regions. 



Observations by the methods described in the previous bulletin were made in 

 cooperation with several experiment stations on the effect on evaporation with 



