BOOKS AND CURRENT LITERATURE 223 



Quamoclidion multiflorum gave results similar to those previously ob- 

 tained hy this method 2 and by the method of "relative transpiration." 3 

 The latter method, as will be remembered, consists essentially in deter- 

 mining the ratio of the rate at which a plant gives off water to the rate 

 at which a standardized atomometer loses water by evaporation. To 

 obtain a preliminary idea of the relative magnitudes of the diurnal and 

 nocturnal indices of transpiring power, day and night observations were 

 made upon a number of plant forms. There was found to be a broad 

 range in the day-night ratio. The direction of the variation was found 

 to be especially interesting: in the case of the more xerophyllous forms 

 the ratio was generally less than unity; while it was usually greater than 

 unity for the more mesophyllous forms. 



Plants of Verbascum thapsvs furnished opportunity for comparison 

 of the relative transpiring powers of leaves upon the same stem but at 

 different heights above the ground. The indices obtained for upper 

 and lower .surfaces, and the averages of these indices (representing the 

 whole leaf surface) showed that the lower, older leaves exhibited lower 

 transpiring powers than did the higher, younger ones. A necessary 

 conclusion was that position upon the stem and age of leaves may be 

 important in determining transpiring power, and also that an adequate 

 idea of the foliar transpiring power of the plant as a whole can only be 

 obtained by tests of a fairly large number of leaves. Tests upon trans- 

 piring power of floral parts showed that there was variation in this 

 characteristic between different species, but that floral and foliar trans- 

 piring power were of about the same order of magnitude in plants of 

 the same species. 



Wilting has deservedly received much attention at the hands of in- 

 vestigators of the water-relations of plants, and studies here reported 

 by Bakke upon wilting plants indicate that the method of standardized 

 cobalt chloride paper should prove of great value in the study of this 

 phenomenon. These studies showed that there is a marked fall in 

 transpiring power as the plant wilts. Furthermore, they indicate that 

 the time required for wilting in the case of plants surrounded by air 

 having a high evaporating power is longer than that required with low 

 evaporation rates, but that the amount of decrease in transpiring power 

 is greater in the latter case. The author suggests that the need of 



2 Livingston, B. E., The resistance offered by leaves to transpirational water 

 loss. Plant World 16:1-35. 1913. 



3 Idem, The relation of desert plants to soil moisture and to evaporation. Pub- 

 lication 50 of the Carnegie Institution, 190G. 



