359 
the Intrinsic Transpiring Power of the Plant. 
changes of wind velocity. In other words, the influence of air movements 
upon transpiration cannot be eliminated by comparing the transpiration 
rate with the rate of water loss from an atmometer. 
This method of comparison can, however, be used to eliminate the 
influence of changes of temperature and relative humidity on transpiration, 
since these two factors act equally upon the rate of transpiration from 
a plant and evaporation from an atmometer. It is clear that only when 
wind velocity is constant does ‘relative transpiration’ give a satisfactory 
measure of the intrinsic transpiring power of a plant. 
Literature cited. 
1. Bakke, A. L. : Studies on the Transpiring Power of Plants as indicated by the Method of 
Standardized Hygrometric Paper. Journal of Ecology, vol. ii, p. 145, 1914. 
2. Blackman, V. H., and Knight, R. C. : A Method of Controlling Air Movements in Tran- 
spiration Experiments. Ann. Bot., vol. xxxi, p. 217, 1917. 
3. Briggs, L. J., and Shantz, H. L. : Hourly Transpiration Rate on Clear Days as determined 
by Cyclic Environmental Factors. Journ. Agr. Research, vol. v, p. 583, 1916. 
4. Darwin, Sir F. : On the Relation between Transpiration and Stomatal Aperture. Phil. Trans. 
Roy. Soc., B., 207, p. 413, 1916. 
5. Laidlaw, C. G. P., and Knight, R. C. : A Description of a Recording Porometer and a Note 
on Stomatal Behaviour during Wilting. Ann. Bot., vol. xxx, p. 47, 1916. 
6. Livingston, B. E. : The Resistance offered by Leaves to Transpirational Water Loss. Plant 
World, vol. xvi, p. 1, 1913. 
7. : Atmometry and the Porous Cup Atmometer. Plant World, vol. xviii, 
pp. 21, 51, 95, and 143, 1915. 
8. : The Relation of Desert Plants to Soil Moisture and Evaporation. 
Carnegie Institution, Washington, Publication 50, 1906. 
9. and Brown, W. H. : The Relation of the Daily March of Transpiration 
to Variations in the Water-Content of Foliage Leaves. Bot. Gaz., vol. liii, p. 309, 1912. 
10. and Hawkins, L. A. : The Water-Relation between Plant and Soil. 
Carnegie Institution, Washington, Publication 204, 1915. 
11. Renner, O. : Beitrage zur Physik der Transpiration. Flora, vol. c, p. 451, 1910. 
12. Shreve, E. B. : The Daily March of Transpiration in a Desert Perennial. Carnegie Institution, 
Washington, Publication 194, 1914. 
