34 



BURTON EDWARD LIVINGSTON 



ous indices are very widely separated in the numbered series, 

 e.g., Ruellia (4, 19), Sorghum (8, 24), Rhus (1, 20), etc. 



The total range of the series of indices is surprisingly great, 

 from 0.009, and below, to 0.760. One leaf surface could supply 

 moisture to the air over seven-tenths as fast as a water surface 

 blanketed by a millimeter of air and another could supply it only 

 nine-thousandths as rapidly as this water surface. 



The data here given are to be regarded merely as a series of 

 more or less representative samples of the indices of transpiring 



TABLE 7 







INDEX OF TRANSPIRING POWER 



PLANT 



TIME AND PLACE OF OBSERVATION 



Upper leaf 



Lower leaf 



Entire leaf 







surface 



surface 



surface 





22 hrs.. July 25, 1911, Tucson 



0 .020 (4) 



0.009 (2) 



0.014 





12 hrs., July 26, 1911, Tucson 



0.072 (14) 



0.112 (18) 



0.092 



Datura 



24 hrs., Sept. 3, 1911, Tucson 



0.027 (5) 



0.016 (3) 



0.021 





15 hrs., Sept. 2, 1911, Tucson 



0.295 (22) 



0.453 (26) 



0.374 



Marty nia 



11 hrs., Sept. 17, 1911, Tucson 



0.680 (28) 



0.760 (29) 



0.720 



Zea 



11 hrs., Sept. 17, 1911, Tucson 



0.064 (13) 



0 061 (12) 



0.063 



Phaseolus, pri- 











mary leaves. . . 



17 hrs., Sept. 9, 1911, Tucson 



0.031 (6) 



0.108 (17) 



0.070 



Secondary leaves 



17 hrs., Sept. 9, 1911, Tucson 



0 .0.53 (11) 



0.112 (18) 



0.083 



Ruellia 



23 hrs. , Sept. 12, 1912, Tucson 



0.038 (8) 



0.033 (7) 



0.036 





16 hrs., Sept. 12, 1912, Tucson 0.020 (4) 



0.124 (19) 



0.072 



Nicotiana 



12 hrs., Sept. 1, 1912, between 











Tucson and Oracle 



0.052 (10) 



0.094 (15) 



0.073 



Sorghum 



4 hrs., Aug. 31, 1912, Tucson 



0.043 (8) 



0 .303 (24) 



0.173 



Rhus 



12 hrs., Sept. 8, 1912, Oracle 



(Indeterm. 











very low) (1): 0.160 (20) 





Arctostaphylos. . . 



12 hrs., Sept. 8, 1912, Oracle 



0.020 (4) 



0.098 (16) 



0.059 



Sphaeralcea 



13 hrs., Sept. 8, 1912, Oracle 



0.378 (25) 



0.469 (27) 



0.424 





13 hrs., Sept. 9, 1912, Tucson 



0.289 (21) 



0.302 (23) 



0.296 



power which occur in the plant kingdom. Many more tests 

 will have to be carried out before reliable generalizations may be 

 attempted, but it seems clear that we have before us evidence 

 enough to warrant the further prosecution of this line of inquir5^ 

 Students of ecology have devoted many hundreds of pages 

 to attempts toward a classification of plants on the basis of their 

 water relations, using as criteria almost wholly the more or less 

 superficial appearance, on the one hand, of the habitats in which 



