AGRICULTURAL BOTANY. 33 



alone. Potassium cblorid, magnesium sulphate, and calcium chlorid were found 

 to be extremely toxic wbeu used singly, but mixtures of any two were less 

 toxic than a solution of a single compound. Good growth was obtained only 

 when the salts of all three metals were present In favorable proportions. The 

 toxicity of magnesium sulphate was completely counteracted by potassium 

 chlorid or by calcium chlorid. Weak solutions of some of the toxic salts were 

 improved by the addition of animal charcoal or colloidal platinum, and it seems 

 the effect of powdered calcium carbonate in counteracting the toxicity of th^ 

 initrient salts was due in part to the adsonitive action of the solid. 



Recent studies on gaseous exchanges of green plants with the atmosphere, 

 L. Maquenne axxd E. Demoussy (Nouvelles Recherches sur les Echanges 

 Qazeux des Plantes Vertes avec V Atmosphere. Paris, 1913, pp. 166, pis. J/, figs. 

 3). — This is a somewhat detailed account of the authors' more recent work 

 (E. S. R., 20, p. 27). It includes findings and deductions from studies, chiefly 

 on Euonymus japonica, regarding respii-ation of leaves under different condi- 

 tions, such as darkness and A'ariable pressure, also an exposition of methods 

 employed in measuring respiratory coefficients of the influence of carbon dioxid 

 contained in the air, of chlorophyll activity, etc. Of the more general con- 

 clusions stated at some length a few may be summarized as follows: 



The respiratory coefficient of leaves is variably influenced by age and activity 

 of the tissues; also by illumination and temperature, given degi'ees of which 

 correspond to the chemical composition noted in the plant and are apparently 

 related to the activity of diasta.ses therein. When a plant is in equilibrium 

 witli external conditions there exists a simple relation between the real respira- 

 tory quotient thereof, its coefficient of absorption for carbon dioxid at the ex- 

 isting tempei'ature, the density of the charge within the apparatus, and the 

 apparent respiratory quotient in the same conditions, this relation permitting 

 the approximate calculation of one of these magnitudes when the others are 

 known. 



The coefficient of absorption of carbon dioxid by green plants varies with 

 temperature according to the law of solubility therefor. It appears to be for 

 thin leaves about double the coefficient of solubility of pure carbon dioxid, 

 which thus appears to supersaturate the cellular structure. The phenomenon 

 of assimilation does not sensibly modify the relations between hydrogen and 

 oxygen in the composition of vegetable tissues. The variations of ratio noted 

 in gaseous exchanges, diurnal or nocturnal, between a plant and the atmosphere 

 and consequently the changes of composition in the plant organs, are thought 

 to be attributable mainly to the influence exerted by heat. 



The respiration of plants under various electrical conditions, R. C. Knight 

 and J. H. Pkikstley (Ann. Bot. [London], 2S (1914), No. 109, pp. 135-161, 

 figs. 6). — ^The authors state that field trials on the effect of electrical conditions 

 upon plant growth (E. S. R., 23, p. 326) have suggested that an increased 

 crop or an earlier ripening may be the result of such treatment. In the pres- 

 ent paper an attempt has been made to analyze this apparent effect by deter- 

 mining the effect of such electrical conditions xipon respiration. 



The experiments have shown that direct currents of a density 10" to 30"* 

 amperes have no effect on the respiration of peas other than that due to 

 accompanying changes of temperatui'e. Overhead dischai-ges producing a cur- 

 rent of density less than 3X10-° amperes have no effect on respiration. When 

 higher currents were employed a definite increase of carbon dioxid was ob- 

 served, which is attributed wholly to the rise of temperature caused by the 

 discharge. In the field, where the currents are too small to produce any 

 appreciable rise of temperature, the authors are of the opinion that electrifica- 



