32 



BURTON EDWARD LIVINGSTON 



between those for the upper surface. In spite of pronounced 

 differences in appearance, the two leaf surfaces at the lower sta- 

 tion possessed almost identical indices of transpiring power. At 

 the upper station these two indices differ widely. 



CONCLUSIONS 



As has already been pointed out, the method of the hj-gro- 

 metric paper tests promises to be of value in the determination of 

 the diurnal fluctuations 'in the transpiring power of many plant 

 surfaces, and appears to furnish at least a possible and practicable 

 alternative to the method of the relative transpiration ratio. In 

 this particular the new method is available in purely scientific 

 studies, whereby the causal relations between external and inter- 

 nal conditions are to be estabhshed and fundamental principles 

 are to be sought. 



Also the new method puts it in the power of the student approx- 

 imately to measure and compare the internal conditions of differ- 

 ent plants, or of the same plant at different times, in regard to 

 one very important feature of the exceedingly complex water 

 relation. In certain respects the criterion of transpiring power 

 should be at least as valuable in plant comparisons as are those of 

 color, form, size, etc., upon which the descriptive botany of the 

 past has almost wholly relied. Here appears to be a simple 

 means by which to compare certain physiological possibilities 

 of different indi\'iduals or forms. 



One of the main points in regard to which the method of the 

 standardized hygrometric paper is to be regarded as a forward 

 step, lies in the fact that it makes possible the study of the relative 

 transpiring power in the case of plants growing in the open soil. 

 That the results are confessedly only roughly approximate and 

 that the method itself is somewhat tedious in apphcation, are 

 not facts of primary importance when it is remembered that the 

 relative transpiration ratios, always derived from potted plants 

 or cut portions of plants, have heretofore furnished our only 

 satisfactory means for acquiring quantitative knowledge of the 

 power of plant surfaces to supply water to the aerial surroundings. 



Turning now to the results of the series of selected experiments 

 which precedes the present section, we note that the transpiring 



