12 



5- The graphs in Figure 2y (PI. XV) show relatively high rates 

 of evaporation when compared with the rates in other portions of the 

 ravine. The average amounts of evaporation per day at the foot, 

 middle, and head of the gully, or wash, were 8.93 c.c, 8.31 c.c., and 

 9.32 c.c. respectively. The evaporation on the gully slope shows less 

 gradation than on the mesophytic slopes of the ravine, the differ- 

 ence between the average at the foot and the head of the gully being 

 only .39 c.c. The evaporation on the gully slope was about the same 

 as that in the oak uplands, which was 8.78 c.c. per day for the season. 

 There is no question that during certain parts of the day the evapo- 

 ration was greater on the gully slope than in the oak uplands. These 

 high rates of evaporation on this slope suggest a vegetation with a 

 xerophytic aspect (see p. 5). In the early part of the summer the 

 gully slope was nearer devoid of vegetation than during the latter 

 part of the season. Reference has been made in an earlier part of 

 tiiis paper to the luxuriance of the late-summer flora of the 

 slope (PI. II, Fig. 3). These changes in the vegetative conditions 

 M'Ould tend to account for the special variations in the graphs for the 

 gully slope, the presence of abundant vegetation about the atmom- 

 eter tending to check the evaporation and its absence tending to in- 

 crease the evaporation relatively. 



6. A comparison of all the graphs, with the exception of those 

 for the station in the open uplands and the stations on the gully 

 slope, shows a remarkable similarity in the variation of the average 

 daily loss for the weekly intervals, the minimum evaporation occur- 

 ring during the week preceding August 16 and the maximum during 

 the week preceding September 12. The graphs for the station in the 

 open uplands and the stations on the gully slope show that the lowest 

 rate of evaporation was during the same week as for the other sta- 

 tions, while the highest rate for the open uplands was during the 

 week preceding August 2, and for the stations on the gully slope 

 high rates occurred during the weeks preceding July 12 and 26, and 

 August 2 and 31, as well as during the week preceding September 12. 



SUMMARY AND C0NCI<USI0N 



The average daily evaporation rate for any weekly period was 

 greater in the embryonic ravine than that for the corresponding 

 weekly period in the narrow ravine; almost always greater in any 

 portion of the broad ravine with mesophytic slopes than in the nar- 

 row ravine; greater near the top of slopes of mesophytic portions of 

 ravine than near the floor ; generally greater at the middle of the 

 southeast-facing slopes than at the middle of the opposite slope ; al- 



