386 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



substance of indefinite composition except the agar itself, and thus it is specially 

 adapted to quantitative work. The soil extract gelatine is more suitable for 

 qualitative work, and is recommended as a preliminary medium in the study of 

 soil bacteria. 



Four other media have been compared with the above. They are these 

 media recommended by Fischer, by Lipman and Brown, by Temple, and by 

 Brown, They are all distinctly inferior to gelatine for qualitative purposes, 

 while for quantitative purposes they are unsuitable, because they contain 

 substances of indefinite chemical composition. 



It has, however, been found that no one of the five agar media has a distinct 

 advantage over any of the others in the matter of the total counts obtained by 

 their use. — A. B. 



Soil Bacteria, InSuence of, on Plant Growth. By H. L. Russell {U.S.A. 

 Exp. Stn., Wisconsin, Rep. 1913 ; pp. 19-21). — Pure cultures of various kinds of 

 soil bacteria grown in extracts from marsh soil previously cropped to corn, oats, 

 or clover, in all cases showed increased bacterial development, this being greatest 

 in the soil cropped to corn. The extracts from cropped loam and sandy soils, 

 on the contrary, invariably retarded bacterial development. It was also found 

 that the growth of different kinds of soil bacteria in a previously sterilized soil 

 produced changes which in some cases increased, and in others decreased, the 

 growth of plant seedlings when grown in extracts from these soils. It is thought 

 that some new light may be thrown on the complex processes concerned in crop 

 rotation. — A. P. 



Soil, Bacteria of Frozen. By H. Joel Conn (U.S.A. Agr. Exp. Stn., New York, 

 Tech. Bull. 35, July 1914, pp. 1-20; 4 graphs). — As a result of his experiments 

 the author deduces the following : — 



1. The number of bacteria in frozen soil is generally larger than in unfrozen 

 soil. This is true not only of cropped soil, but also of sod and fallow soils. 



2. The increase in the number of bacteria after freezing is not due to the 

 increase in soil moisture which usually occurs in winter. 



3. The same increase in germ content may take place in potted soil, where 

 there is no possibility that the bacteria are carried up mechanically from lower 

 depths during the process of freezing. 



4. It is probable that an actual growth of bacteria occurs when the soil is 

 frozen. The influence upon fertility is still an unknown factor. 



The methods employed were as follows : — Soil samples were obtained by boring 

 6 inches and were then thoroughly mixed by sifting or stirring if dry or muddy. 

 •5 grm. of the sample was then shaken up with 100 c.c. of sterile water and a 

 series of dilutions, 1 : 100,000 and 1 : 200,000 or 1 : 200,000 and 1 : 500,000, were 

 sown on a gelatine plate. 



The medium used was gelatine 12 per cent., soil extract 20 per cent., 

 dextrose 1 per cent., and adjusted to -5 per cent, normal acid to phenolphthalein. 



To obtain the soil extract, soil was heated for one hour at atmospheric pres- 

 sure, then mixed with an equal weight of cold water, allowed to stand overnight, 

 then boiled for half an hour and filtered. — A. B. 



Soil Moisture, The Storage ;ani Use of. By W. W. Burr [U.S.A. Exp. Stn., 

 Nebraska, Research Bull. 5, March 1914 ; Bull. 170, July 1914 ; 15 charts; 

 4 illus.). — The above research bulletin probably comprises the most exhaustive 

 work of its kind that has so far been carried out, to determine the factors that 

 control soil moisture. In the results it is suggested that autumn tillage, after crop 

 has been removed, would prove very beneficial in retaining the soil moisture 

 for another season. 



Although not recommended under all conditions, the making and retention 

 of a soil mulch during growing season is strongly recommended, but under all 

 conditions the removal and destruction of weeds is insisted on as necessary 

 to allow a crop to grow into proper maturity during dry weather. 



Incidentally it is mentioned that oats, spring wheat, barley, and corn will 

 seek water to a depth of 6 to 7 feet, perennial grasses to an even greater depth, 

 while alfalfa will go down to natural water level to seek water at depths of 

 20 to 30 feet.— C. P. C. 



Soil Sterilization, Methods of, for Plant Beds and Greenhouses. By A. D. 



Selby and J. G. Humbert (U.S.A. Agr. Exp. Stn., Ohio, Cir. 151, Jan. 1915, 

 pp. 65-74; 2 figs.)- — The methods of soil sterilization are essentially three in 



