of the air and the soil-moisture content at the stations selected ; and 

 finally, as the third and last step, the interpretation of results. 



Location and Description of the Stations 



In this study seventeen different stations were established; fifteen 

 in the ravine, one in the oak uplands, station 16, and still another in 

 the open uplands, station 17 (PI. IX, Fig. 15), the vegetable garden 

 of the McLeish estate. The fifteen stations in the ravine were lo- 

 cated, speaking generally, as follows: Station 1 (PI. I, Fig. 2) in an 

 embryonic ravine; station 2, in a portion of a ravine, with lateral 

 cutting delayed, forming a miniature clay canon; stations 3 (PI. I, 

 Fig. 1), 4 (PL HI, Fig. 5), 5 (PI. IV, Fig. 6), 6 (PI. V, Fig. 8). 

 and 7 (PI. VI, Fig. 9), in the part of the ravine with the mesophytic 

 forest vegetation on the slopes; stations 8 (PI. IV, Fig. 7), 9 (PI. 

 VII, Fig. 10), 10 (PI. VII, Fig. 11), 11 (PI. II, Fig. 4), and 12 

 (PI. VIII, Fig. 12) in a portion slightly less mesophytic than the 

 preceding; and stations 13 (PI. VIII, Fig. 13), 14 (PI. II, Fig. 3), 

 and 15 (PI. IX, Fig. 14), on the slopes of a wash or gully near the 

 mouth of the ravine. The specific geographical location of each of 

 these stations in the ravine and its tributaries and also of those in the 

 oak and open uplands is shown on the surface map (PI. XVIII), while 

 the angle of slope, direction of exposure, and soil and vegetation char- 

 acteristics are enumerated in the following tabular summary. 



The "wilting coefficient" — a term used by Briggs and Shantz 

 ('12: 9) to represent the moisture content of a soil corresponding to 

 the wilting point of a plant — for various soils in the McLeish ravine 

 was correlated with the soil-moisture equivalent by an indirect method 

 devised by these authors ('12:56-57). This coefficient indicates 

 the limit of soil-water content above which growth must occur, al- 

 though plants will live and continue to draw water below this point. 



In listing the dominant vegetation of each station the emphasis 

 was placed on the herbaceous forms and the seedlings of shrubs and 

 trees because they are a much better index of present ecological con- 

 ditions than the mature trees. 



Measurement of the Evaporative Power of the Air 



The instrument that was used to measure the evaporative power 

 of the air in the different stations was the Livingston ('10) porous 

 cup. The structure and operation of this simple instrument have 

 been so well set forth by the inventor and others that have used it for 

 scientific purposes that an explanation of its management would be 



