1916] CURRENT LITERATURE 77 
secured during 1908 and 1910, and a more complete set of observations was 
obtained during the summer of 1911. ‘These results are expressed in an inter- 
esting series of graphs, with evaporation rates ranging from approximately 
toocc., per day from the standard atmometer at 3000 feet during April and 
May, and half that amount during the more humid July and August, to about 
15 cc. per day during the latter months at 8000 feet. The need of data from 
a larger number of stations for a series of years is recognized, but from those 
obtained the following conclusions are drawn: (1) the rate of evaporation 
through the arid and humid summer seasons is about 3.5 times as great on the 
desert as it is at 8000 feet; (2) the rates of evaporation are approximately half 
as arent in humid midsummer as aner x are in soadoes eet @) at i ne 
and h higher 
_ and (4) the difference etenen the amounts of tion on north and south 
slopes becomes greater with increase of altitude in x proportion to the amounts 
of each. Corresponding with the high rates of evaporation are low values 
of relative humidity. A considerable amount of temperature data has been 
secured, its most important siete? having to do with the altitudinal enresy 
ing of the frostless season, the altitudinal fall in temperature, the daily 
and minima at various altitudes, and the absolute minima of winter.  Pisbae 
data show that the lowest temperatures of winter (—2° in 1913 and 15°5 F. 
in 1914 at 7600 feet) are less severe on the Santa Catalinas than on the plateau 
of north central Arizona. The departure from the normal altitudinal gradient, 
due to the operation of cold air drainage, discussed in an earlier paper? and 
reviewed in this journal, is supported by further data, and its importance in 
influencing vegetation is noted, and some soil temperature data seem to indi- 
cate that its winter minimum is decidedly above that of the air. With such 
remarkable variety in vegetation and such extremes in physical factors, the 
correlation of vegetation and its controlling factors become of the utmost 
importance, and in no part of this report is the excellence of the work better 
shown than in SHREve’s discussion of the complex problems involved. it 
such a large gradient of climatic change, it might be expected that vertical 
distribution of species would be decidedly limited, and such is the case. No 
plant extends its range from the desert to the upper forest, and very few extend 
through half that gradient of conditions, while in general it may be said that 
most are limited to vertical ranges of less than 1500 feet in habitats of the same 
topographic character. A vertical range of 4700 feet for Vitis arizonica in 
canyons and ravines, 4200 feet for Agave Palmeri from the dry slopes at 3200 
feet to high open ridges, and Juniperus pachyphloea from northern slopes at 
4200 feet to ridges at 7900 feet are among the more extreme instances given. 
Moisture is recognized as the most critical factor controlling the vertical distri- 
bution of this vegetation, and the ratio of evaporation to soil moisture is 
* SHREVE, Forrest, Cold air drainage. Plant World 15:110-115. 1912. 
3 Bor. Gaz. 5§:263. 1913. 
