

niPROVEMEXTS IX THE IMETHOD FOR DETERMIN- 

 ING THE TRANSPIRING PO\^TR OF PLANT 

 SURFACES BY HYGROIVIETRIC 

 PAPERS 



BURTON E. LIVIXGSTOX 

 The Johns Hopkins University, Baltimore, Maryland 



AXD 



EDITH B. SHRE^'E 

 The Desert Laboratory, Tucson, Arizona 



IXTRODUCTIOX 



Several features of the method emploA-ing cobalt chloride 

 paper- for measuring the transpiring power, ^ or coefficient of 

 transpiration, of leaves have recently been considerably im- 

 proved, and some of these improvements are here presented.'* 



1 Botanical contribution from the Johns Hopkins University', Xo. 53. 



- Stahl, E., Einige Versuche iiber Transpiration und Assimilation. Bot. 

 Zeitg. 52: 117-146. 1894. Livingston, B. E.. The resistance offered by leaves 

 to transpirational water loss. Plant World 16: 1-35. 1913. Bakke. A. L., 

 Studies on the transpiring power of plants as indicated by the method of stand- 

 ardized hygrometric paper. Jour. Ecol. 2: 145-173. 1914. Idem, The index 

 of foliar transpiring power as an indicator of permanent wilting. Bot. Gaz. 60: 

 314-319. 1915. Shreve, Forrest, The transpiring power of plants as influenced 

 by differences of altitude and habitat. Science, n. s. 43: 363. 1916. 



^ Transpiring power is the term used by Li\-ingston to denote the ability of 

 the leaf to give off water vapor. It represents the influence of all the internal 

 conditions (effective within the leaf to accelerate or retard transpiration), stoma- 

 tal conditions being generally important among these. Briggs and Shantz 

 have employed the expression transpiration coeflacient in this same sense. 

 (Briggs, L. J., and H. L. Shantz, Hourlj- transpiration rate on clear days as de- 

 termined by cyclic environmental factors. Jour. Agric. Res. 5: 583-650. 1916.) 

 There seems to be no objection to this term, if it is clearlj- understood that it 

 does not refer to transpiration itself but to one group of conditions (internal 

 ones) that determine the rate of that process. 



^ These improvements are the result of several years of work, to which Miss 

 Aleita Hopping and Mr. E. S. Johnston have contributed, at different times. 

 Miss Hopping' s work has been especially important in the early stages of many 

 of the improvements here set forth. 



287 



THE PLANT WOKLB, VOL. 19, XO. 10 

 OCrOBEB, 1916 



