120 EXPERIMENT STATION RECORD. 



fully used in the nutrition of plants. In every case where there was a production 

 of anunonia in the cultures the fernientation was due to the entrance of secondary 

 organisms. Where there was an absolute absence of inicro-organisms the fungi were 

 able to develop without the formation of anmionia, depending upon the amids present 

 in the solution. The soluble ferments secreted by As2)ergilhi.'i niger, A. repens, and 

 Penicillium glaucum were incapable of transforming the amids to ammonium salts. 



The electrical conductivity of plant juices, F. De F. Heald {Ahs. -in Science, 

 n. ser., 15 {1902), No. 377, }>. 457). — By using the methods of physical chemistry the 

 author investigated the conductivity of the juice expressed from the leaves, stems, 

 and roots of beets, potatoes, onions, radish, cucumbers, purslane, water lilies, and 

 rough pigweed. Ash determinations were also made for the juices used, and the ash 

 redissolved in distilled water and diluted to the original volume of the juice from 

 which it Avas obtained. The specific conductivity was determined for the ash solu- 

 tions. It was found that plant juices are comparatively good conductors, the con- 

 ductivity being due in a large measure to the dissolved mineral substances, the organic 

 compounds playing a minor part. The conductivity of juice obtained from the roots 

 of plants is always less than that of the juice obtained from the subaerial parts of the 

 plant. The specific conductivity generally increases progressively from the root 

 upward, although in some cases the sap from the stem has a higher conductivity than 

 that from the leaves. In most cases the specific conductivity may be taken as a rough 

 measure of the relative amount of ash present in the different parts of the plant. 



The sensory area of the roots of land plants, F. C. Newcombe {Abs. in Science, 

 n. ser., 15 [1902), No. 377, pp. 454, 455). — The sensitiveness to external stimuli on the 

 part of roots of land plants has generally been considered as confined to the apex and 

 elongating zone. In nearly all species this would be confined to the first 10 mm. of 

 the apex. In studying the phenomena of rheotropism the author found that the 

 region of the root posterior to the elongating zone is sensitive. To determine the 

 location of the sensory tissue, various parts of the root were shielded from the flow 

 of water ]iy inclosure in glass tulies. The roots of radish, white nuistard, buckwheat, 

 sunflower, and popcorn gave rheotropic curves when stinuilated at a distance of 10 to 

 1.5 mm. from the limit of the elongating zone. 



The significance of transpiration, C. R. Barnes {Aha. m Science, n. ser., 15 

 {1902), No. 377, p. 460). — In this paper the author seeks to present a new point of 

 view regarding transpiration. Ordinarily the purpose of transpiration is held to be 

 a double one: First, to cause the influx to the leaves of a large amount of water, 

 thereby supplying the leaves with a sufficient amount of mineral salts; and second, 

 to concentrate the extremely dilute solutions and thus get rid of the surplus water. 

 The author claims that the amount of salts absorbed is dependent ujjon the living 

 cortex of the rootlets and the mesophyll of the leaves. If the cortex is freely per- 

 meable, equilibrium in the distribution of any salt will occur without evaporation 

 from the aerial parts. If, then, evaporation concentrates the solution, the higher dif- 

 fusion tension of the salt will tend to drive it to those regions where the diffusion 

 tension is lower. This tendency, therefore, would operate against the further supply 

 of that material to the leaves. If the cortical layers of the roots be not freely perme- 

 able, the amount absorbed is regulated wholly by protoplasmic acitivity and is not 

 directly affected by outside supply. The phenomena of selective absorption show 

 that transpiration does not determine the amount of salts absorbed. Wet cell walls 

 exposed to the atmosphere are indispensable for the solution of the necessary gases, 

 the plant being unable to render waterproof the cell walls so long as gas absorption 

 is necessary. Transpiration is, therefore, considered as unavoidable, although in 

 itself a constant menace to the life and activity of the plant. Advantage is doubt- 

 less taken of the xylem bundles to facilitate the movement of substances lield in 

 solution, but the author claims there is no reason to think that this is essential. In 

 addition to the above, attention is called to the fact that transpiration has also 



