732 EXPERIMENT STATION RECOED. [Vol.35 



Vegetative succession under irrigation, J. F. Macbbide {U. f>. Dept. Agr., 

 Jour. Agr. Research, 6 {1916), No. 19, pp. 741-760, pis. 8). — In a contribution 

 from the Wyoming Experiment Station, the author gives an account of observa- 

 tions on vegetative succession under irrigation on a ranch in Albany County, 

 Wyo. 



In order to increase the yield of hay from this ranch, irrigation was resorted 

 to, and it was found that the artificial formation of natural meadows is brought 

 about by a gradual change divisible into several stages each of which is charac- 

 terized by one or more particular species of plants. The relative permanence 

 of these stages may be controlled by regulation of the water supply. Agropyron 

 spp. and Deschampsia cwspitosa are said to furnish the most valuable hay. 



A single climatic index to represent both moisture and temperature condi- 

 tions as related to plants, B. E. Livingston {Abs. in Science, n. set., 43 {1916), 

 No. 1106, p. 362). — A method is described by which the indexes of precipitation, 

 atmosplieric evaporating power, and temperature efficiency for plant growth for 

 any period of time may be combined into a single index of moisture-tempera- 

 ture efficiency. Based on this index, a new climatic chart of the United States 

 for the period of the average frostless season has been prepared. 



A living climatological instrument, B. E. Livingston and F. T. McLean 

 (Abs. in Science, n. ser., 43 {1916), No. 1106, pp. 362, 363).— The authors de- 

 scribe a method for comparing the efCectiveuess of climates in promoting the 

 growth of standard plants. 



In these experiments soy beans were grown in pots always filled with the 

 same kind of soil, the seed being soaked in water at a given temperature for a 

 certain time before planting. Measurements were made on the plant after two 

 and again after four weeks, when the cultures were discontinued. New cul- 

 tures were started every two weeks and the climatic efficiency for plant growth 

 was determined from the plant measurements made after two and four weeks. 

 The value of the climate for any two to four week period at any station may be 

 compared v/ith that for any other period at the same or at any other station. 



The daily march of transpiring power as indicated by the porometer and 

 by standardized hygrometric paper, S. F. Tret.ease and B. F. Li\t:ngston 

 (Abs. in Science, n. ser., 43 (1916), No. 1106, p. 363).— The authors have deter- 

 mined the transpiring power of the lower surfaces of Zebrina leaves by means 

 of standardized cobalt chlorid paper, and at the same time porometer readings 

 were made. 



It was found that the porometer rates furnish data for deriving stomatal 

 diffusive capacity, but that this capacity is not quite proportional to transpiring 

 power. Transpiring power was found mainly dependent upon the degree of 

 stomatal opening, but other conditions were influential. 



The transpiring power of plants as influenced by differences of altitude and 

 habitat, F. Sheeve {Abs. in Science, n. ser., 43 {1916), No. 1106, p. 363).— Meas- 

 urements w^ere made of the transpiring power of the leaves of some 20 species 

 of plants in the desert and encinal regions of the Santa Catalina Mountains in 

 southern Arizona in the arid foresummer of 1915. The species investigated 

 belonged to different life forms, which were found to differ in their transpiring 

 power and in the character of its daily changes. The same species exhibited 

 a higher transpiring power in the individuals which grow in the flood plains 

 than in those which grow on arid slopes. The daily changes in the former 

 individuals are concordant with the daily march of evaporation, while in the 

 case of the latter the transpiring power falls sharply before the daily maximum 

 of evaporation is reached. A comparison of the transpiring power of the same 

 species at different elevations has shown that the daily check is applied earlier 



