AGEICUL.TUBAL, BOTANY. 633 



took certain position between and 90°. The geotropic disposition of the roots 

 remained constant throughout in the agar medium, so that the intensity of 

 the curving depended only on the intensity of the diffusion forces or stimuli, 

 and this varied with the nature of the salt or diffusion substances used, with 

 the concentration, with the thickness of the agar block, and with the length of 

 time the diffusing currents acted. 



The form of the curving was determined by the point on the root at which 

 the curve occurred and the appearance of the curved line. Some curves were 

 localized near the root tips and were sharply angular, while others began in 

 the higher zones of the root and were bow-shaped. Between these two ex- 

 tremes there were different transition forms. 



The reaction as to the direction of the curvature, due to the concentration, 

 manifested itself by a check in the growth and a positive curvature of the roots. 

 This effect was observed generally in all substances tested, both electrolytic 

 and nonelectrolytic. When the concentration became greater a difference be- 

 tween the reaction to electrolytic and nonelectrolytic substances manifested 

 itself. In diffusion streams of nonelectrolytic content the roots in general 

 were unaffected. In the case of electrolytic substances there was observed a 

 dominant direction curve which was positive in the case of acids, alkalis, 

 sodium carbonate, and potassium carbonate, and negative in the case of neu- 

 tral salts. The differences in curvature are referred to the action of individual 

 electrolytes. A strong positive curve was generally observed in alkaline solu- 

 tions, while acids produced positive but weak curves. Positive curvatures 

 were probably due to the presence of H and OH ions, while the negative curve 

 seemed to depend on the strength of the solution independent of the nature 

 of the cation. Salts with divalent cations, as magnesium and strontium, pro- 

 duced, independently of the nature of the anion, a negative curve. Salts with 

 univalent cations, as lithium, sodium, potassium, and ammonium, showed less 

 negative curvature. 



The article closes w^ith tables showing the effects of each substance used 

 on the root curvatures and with a general discussion of the results obtained. 



Researches on the formation of nitric acid in living cells, P. Maz^! ( Compt. 

 Rend. Acad. Sci. [Paris], 152 {1911), No. 23, pp. 162^-1621) .—The author 

 claims that 6 species of bacteria, some aerobic and some anaerobic, form nitric 

 acid when grown in a medium consisting of ammonium chlorid, tripotassium 

 phosphate, magnesium sulphate, iron sulphate, sodium chlorid, calcium car- 

 bonate, saccharose, and water. 



On the assimilation of atmospheric nitrogen by green plants, Eva Mameli 

 and G. Pollacci (Atti R. Accad. Lincei, Rend. CI. Sci. Fis., Mat. e Nat., 5. ser., 

 20 (1911), I, No. 9, pp. 680-6S7; Bui. 8oc. Bot. Ital., 1911; No. 2, pp. 16-21; ahs. 

 in Naturio. Rundschau, 26 {1911), No. 38, pp. 48It, 485).— This is a further 

 study (E. S. R., 24, p. 29) of the fixation of free nitrogen by green plants, in 

 which seedlings of Acer negundo, 8olanum nigrum, CucurUta pepo, Raphanus 

 sativus, and Polygonum fagopyrum were grown in sterilized nitrogen-free media. 

 Tabulated results are given of the amount of nitrogen in each plant compared 

 to that in the seed from which they grew. 



The authors claim as a result of these experiments that under special condi- 

 tions the power of assimilating free nitrogen is possessed by many green plants. 



On the need of lime salts in the metabolism of the fungus Coprinus, J. R. 

 Weib (Flora, n. ser., 3 (1911), No. 1, pp. 81-90). — As a result of experiments 

 the author concludes that lime compounds are as necessary for the life and 

 development of the higher fungi like Coprinus as for the higher algje and other 

 green plants. 



