734 EXPERIMENT STATION EECORD. 



nitrogen, ammonification, deuitriflcation, and reduction of nitrates by soil 

 bacteria. 



The number of bacteria per gram of 70 samples of soil was determined by 

 growing the organisms in nutrient agar and Ashby's nutrient medium for the 

 fixation of nitrogen by Azotobacter. Studies on the fixation of nitrogen by 

 impure cultures, availability of various compounds effecting nitrogen fixation, 

 ammonification, reduction of nitrates, bacterial content of subsoil, etc., are 

 described. In the study of nitrate reduction 201 species of organisms from 

 various sources were examined and 139 were found to reduce nitrates to 

 nitrites, while the other species did not effect this reduction. In studying the 

 vertical distribution of bacteria, samples were taken of soil and subsoil to a 

 depth of 20 ft. and a constantly diminishing bacterial content was noted until 

 a level of 13 ft. was reached, when a sudden increase in numbers was observed. 

 The reason for this increase is unknown as no visible impervious layer of soil 

 was encountered. 



Studies on the action of acids and acid salts upon the development of 

 Asperg-illus nig'er, A. Kiesel (Ann. Inst. Pasteur, 21 {1913), No. 5, vi>- 391- 

 Ji20, flgs. 8). — Concluding a fuller discussion of this subject than that previously 

 noted (E. S. R., 27, p. 848), the author gives the following among other con- 

 clusions : 



The physiological activity of various acids and acid salts upon the develop- 

 ment of A. niger does not correspond in the majority of cases to their chemical 

 activity. Fatty acids show considerable toxicity, especially those contiiining 

 much carbon, the molecular structure also apparently being significant in this 

 respect. It appears from several considerations indicated that the differences 

 of toxicity observed in case of some substances tested are due to dift'erences in 

 penetrability of the protoplasmic layer of the cell for various substances, and 

 that the penetration by the body necessary to its toxic effect may be regulated 

 to a certain degree by that layer. In the development of A. niger in the presence 

 of various acids the acid content may first increase and later decrease, while 

 for certain acids augmentation is continual, oxalic acid being only one of 

 several noted as forming under such circumstances. 



The influence of the medium, on the resistance of Penicillium crustaceum 

 to toxic substances, A. Le Renard (Ann. Sci. Nat. Bat., 9. ser.. 16 (1912), 

 No. 4-6, pp. 277-336; ads. in Bot. CentbU 122 (1913), No. 15, pp. 353, 354).— 

 Studying the protective influence exerted by nutritive salts in the culture 

 medium in which a fungus will develop despite the presence of a toxic sub- 

 stance, the author noted the antitoxic efi'ects of a number of nutritive salts 

 employed singly, combined together, or in connection with glucose, the prin- 

 cipal ones being the acetates, formates, sulphates, nitrates, and phosphates of 

 potassium, ammonium, and magnesium. The toxic salts used were acetate 

 and sulphate of copiier and both the chlorid and nitrate of copper, zinc, nickel, 

 cobalt, mercury, and silver. The fungus was P. crustaceum. 



The author concludes that the resistance of this fungus to poisons varies 

 according to the nature and concentration of the nutritive medium in which 

 the fungus is developing. The principal role in the protection of the fungus 

 from the toxic compound may be played by either the acid or the base in the 

 medium, but the action of the base is generally the greater when high con- 

 centrations are employed. 



FIELD CROPS. 



The technique of field experiments, M. L. Mortensen (Jahresber. Ver. 

 Angew. Bot., 9 (1911), pp. 177-187).— The author believes that from 1/200 to 

 1/1,000 hectare (about 535 sq. ft.) is the proper size of plats, and that the 



