1912] GLEASON & GATES—RATES OF EVAPORATION 489 
is usually the earliest one to develop, and later is followed by the 
Eragrostis trichodes consocies. The latter, representing the higher 
development of the association, has an evaporation rate which is 
88 per cent of the lower type. In both cases the amount of evapora- 
tion from the bunch-grass is lower than that from the blowout, 
although the four atmometers were less than 100 m. apart. 
The difference in the rate of evaporation in the bunch-grass and 
Quercus velutina associations is much more marked. Young oak 
trees in different stages of development are present in the former 
. Association 0.20 0.40 0.60 0.80 200 1,20 2.49 .60 
- Blowout (basin) 1.56 
- Blowout (side) 1.27 
- Bunchgrass (Leptoloma consoc.) eR ea 
. Bunchgrass (Eragrostis trichodescon.) 1.04 
Ss a a 
c i, re 
- Quercus velutina woods OE ae re Nei cig - 
Quercus veluti a 
Willows (Acer part) 2s 
- Willows (Salix part) aaa 
- Mixed forest (margin) 0.36 
- Mixed forest (center) 0.29 
Fic. 6.—Diagram showing relative amounts of evaporation in the different 
stations. ; 
association, clearly demonstrating that they are capable of with- 
standing the relatively high prairie rate of evaporation. With 
their growth to maturity, and the consequent succession of the 
bunch-grass by the forest, the evaporation beneath them is steadily 
diminished, until it becomes about 55 per cent of that of the normal 
bunch-grass. Atmometer no. 7 was placed in a typical part of the 
Quercus velutina association (fig. 4). 
With the increase in the age and density of the forest cover, the 
evaporation beneath it is still further reduced. Eventually the 
succession of the mixed forest association begins, and the first indica- 
tion is usually shown by the presence of Psedera quinquefolia and 
Celastrus scandens. Atmometer no. 15 was located in such a place, 
and the diagram shows a reduction in the rate of evaporation from 
0.66 to 0.55, in terms of the standard. The reduction is still 
greater in the typical mixed forest, represented by instruments 
