1919] AGRICULTURAL BOTANY. 133 



growing in water culture the equilibrium concentration was specific for each 

 plant. It is stated that if the concentration is below that which is toxic for 

 the plant, yet meets growth requirement thereof, the equilibrium concentration 

 value is independent of the kind of nutrient salt used, the concentration of the 

 electrolyte, or the volume of the solution. 



At the point of equilibrium between the plant and the solution, the electro- 

 lyte content of the solution is determined (1) by certain factors which are 

 constant for different plants under the same conditions, such as carbon dioxid 

 equilibrium with the air, and (2) by the rate of cleavage of ion-producing 

 compounds of the cell and reabsorption of the ions produced. 



The influence of certain added solids upon the composition and efficiency 

 of Kncp's nutrient solution, E. H. Toole and W. E. Tottingham {Amer. Jour. 

 Bot., 5 (1918), No. 9, pp. 452-461). — Results of experimental tests regarding the 

 effects upon the physiological balance of a nutrient solution produced by adding 

 solids offering relatively large surface to the action of solvents and solutes are 

 given. 



The authors state that when barley and pea plants were grown for 21 days 

 in Knop's nutrient solution plus ferric hydrate, silicic acid, and carbon black, 

 each upon two planes of application, it was found that the first increased the 

 dry weight of the barley tops about 50 per cent, the second had no effect, and 

 the third depressed growth appreciably. The weight and the length of the 

 roots were not markedly affected in any case. The dry weights of barley tops 

 were inversely proportional to the hydrogen-ion concentration of the solution, 

 but the total range in the acidity of the cultures was comparatively small. In 

 all cases the growing barley plants exerted a neutralizing effect upon the reac- 

 tion of the solution. Over 90 per cent of the phosphorus of Knop's solution 

 was removed by the higher application of ferric hydrate, presumably owing 

 to the formation of insoluble ferric phosphate. This culture was by far the 

 best, as regards both appearance and yield. Treatment with ferric hydrate 

 (producing neutrality of the nutrient medium) may have contributed to the 

 higher yield. No clear evidence was obtained regarding adsorption of nutrient 

 ions. 



A simple method of demonstrating' the production of aldehyde by chloro- 

 phyll and by anilin dyes in the presence of sunlight, W. J. V. Osterhout 

 (Amer. .Jonr. Bot., 5 (1918), No. 10, pp. 511-513). — A method is described by 

 which relatively large quantities of aldehyde free from contamination by non- 

 volatile substances is obtained in sunlight from chlorophyll or from certain 

 anilin dyes. 



The origin and physical basis of succulence in plants, D. T. MacDougal 

 and H. A. Spoehr (Carnegie Inst. Washington Year Book, 17 (1918), pp. 85, 

 86). — The discovery that Oastilleja and Erigeron each included some individuals 

 which were thick leafed and some which were thin leafed, and that these leaf 

 characters were correlated with water supply, has furnished a starting point 

 for the study of succulence. An analysis of the carbohydrates of desert plants 

 has shown that when cells containing polysaccharids undergo depletion of water 

 content these sugars are reduced to the pentosans, of which the mucilages are 

 lai'gely composed. This and other facts lead to the conclusion that aridity, by 

 causing undue loss of water, induces a change in the cell by which the amount 

 of water it may hold is greatly increased. This results in giving the cell 

 mass a storage capacity which is permanent, as the pentosans are not i-econ- 

 vertible into the polysaccharids. The change from a thin-leafed condition to 

 that of succulence is not a simple one, and it appears that the resulting biocol- 

 loidal complex of the succulent leaf has taken on new characters. 



