Jfc.1.] gkav ami HOOKEB on THE &OCKT MOUNTAIN FLORA. 11 



Platanus Wriiiltlii. \c, <Jin reus Enaniii and (>. Iiiipolrua, &C. Along 

 with these, as equally foreign to tin* timber region « >i* tin- lo><k\ Mount- 

 ains ami the accessor} ranges, we should eliminate and place 03 them- 

 selves those trees \\ li iili are characteristic <»f tin- Bouthern arid plains, 



rather than of the mountains. A leu 0!' these 001116 into I tali ami 



Nevada, bul they inostlj belong to Arizona, and to a district, which, 

 with all its aridity, recefr es a portion ^( the subtropical Bummer rainfalL 

 To this category belong — 

 (Hnega Zteoto, a peculiar genus of papilionaceous Legumitv 



l\ukinsoiti<i Ti>rr<>/((ita. the Palo Verde [Cercidiuf* of ant horsj. 



rmsojns /((liiiora, the true Bfesquite, ami P, pt/bese, us, the Screw Bean 

 or Screw-pod Mesquite, the pods and seeds of which furnish food and 



. the balk a kind of gum-arabic, and the wood good fuel. 



ggiij the only one which, in this district becomes abores* 



cent. 



Ckilopsis 8aligna,the Desert Willow, fringing water courses in tin? 

 arid district 



.V. ophylla,a Texas Mulberry which extends along the south- 



ern part of New Mexico and Arizona. 



It might he expected that a fair number of trees represented in the 

 inoister and cooler district of the Northern Rocky .Mountains would dis- 

 appear from the scantier, interrupted or scattered or restricted woods of 

 the southern mountains: hut we miss from them only one of the north- 

 ern trees above enumerated, namely, the Larch of the region, Larix 

 n. w hile we miss from the northern mountains no small number 

 ot those in the southern. 



This is not the place to institute a comparison between the Rocky 

 Mountain forest and the eastern; but it ma\ he remarked that, while 

 tspermous, round headed, and deciduous-leaved trees prevail in the 

 latter, largely in the number of species and genera and conspicuously 

 in the extent of surface occupied, the Rocky Mountain sylva, in its char- 

 acteristic features, i^ gymnospernious, spiry, and evergreen. In the 

 importance of its useful products, such as Lumber, the difference between 

 the two BOrtS, as a whole, in the Atlantic forest cannot he .meat, lint 



with perhaps only one exception, thai ot' the so-called Mountain Mm 



■'■minis ledifolius a small tree or more common! j ;i shrub), 



the economical value of the Rocky .Mountain forest is almost wholly in 



- trees, and in the mountains these alone strike the eye. 



Disregarding unessential and inconspicuous features, and eliminating 



those outlying small trees of the Mexican border, we maj say that the 



Rocky Mountain forest is composed of the following species, winch are 



arranged somewhat in the order «»f their conspicuousness ami impor- 



tarn 



I',, i»s pandtrosa^ called Yellow Pine, and sometimes Long Leaved Pine, 

 which distinguishes it well from the next. It is a composite si >c 

 the form of it which we are concerned with, and to winch [£ngeluiann> 



