516 SOILS. 



are conspicuous in the uplands as well. The tall southern cane 

 (Arundinaria macrosperma} , usually considered a plant of the 

 low river bottoms, originally covered the loess or " Cane hills " 

 of the lower Mississippi, with their highly calcareous soils. 

 The same is true of many other trees and shrubs characterizing 

 limy lands. Of course there are some whose habitat is depend- 

 ent upon the concurrent presence of both lime and moisture, 

 such as the sycamore, cottonwood, hackberry, pawpaw, etc., 

 which are naturally found only in stream bottoms or on low 

 hammocks. 



In the arid region, on the contrary, the main difference in 

 upland and lowland vegetation is (outside of mountain in- 

 fluences) entirely referable to moisture-conditions; the proof 

 being that so soon as the uplands are irrigated the lowland 

 flora takes possession. Both uplands and lowlands being 

 abundantly calcareous, there then is no cause for any material 

 differences. This substantial uniformity of upland and low- 

 land plant growth is particularly striking in the comparatively 

 restricted floras of Eastern Oregon and Washington, and in 

 Montana, where the more luxuriant growth of the valleys is al- 

 most the only contrast seen when their vegetation is compared 

 with that of the uplands adjacent. 



Forms of Deciduous Trees in the Arid Regions. Since, as 

 shown above, the soils of the arid regions are almost through- 

 out calcareous, we should expect that the forms of the native 

 trees would in general conform to the rule given above. As 

 regards the deciduous trees this is very generally true : We 

 rarely see on the Pacific slope, south of Oregon, anything to 

 compare with the tall oaks of the Atlantic forests. The native 

 oaks are as a rule of low, spreading growth, with stout, short 

 trunks; and as they rarely form dense forests, the timbered 

 areas have an orchard-like appearance, characteristic of the 

 landscapes of the arid region, from the Mezquit Plains of 

 Texas to Eastern Oregon and Washington. Only where a 

 very abundant supply of moisture prevails do we find occa- 

 sional exceptions. The trees of the humid region when trans- 

 planted to California have a perverse tendency to branch low, 

 so that only the most persistent trimming-up will induce them 

 to form trunks at all like those found in their native climes. In 



