24 BOTANY OF THE DEATH VALLEY EXPEDITION. 



The following shrubs are abundant in this zone: 



Artemisia tri&entaia. Kmzia glandulosa. 



Ccanothus greggii. Jiihcs leptanthum hrachyanthum. 



Garrya veatckii Jlavescens. Salvia caniosa. 



In most cases each pifion or juniper tree stands distinct from its 

 neighbor, and, being well supplied with light on all sides, develops a 

 short trunk and a rounded form, the branches commonly spreading 

 nearly to the ground. 



Between the lower limit of the juniper and the upper limit of Larrea 

 is an interval of transition ground characterized by the growth of the 

 following shrubs: 



Coleogyne ramosissima. Ephedra viridis. 



Dalea polyadenia (in the northern Eurotia Janata. 



part ofthe region). Grayia spinosa. 



Primus fasoiculata (in the ra- Telradymia glahrata. 



vines). Telradymia spinosa. 



It is on this transition ground that Yucca arborescent attains, in the 

 southern portion of the region, its fullest development both in size and 

 numbers. 



Above the piiions and junipers of the Upper Sonoran zone lies a belt, 

 about 800 meters in thickness, to which the name Transition zone has 

 been applied. 1 In the Charleston Mountains it is covered by a forest 

 of Pinus ponderosa scopulorum, and on the eastern slope of the Sierra 

 Nevada by Pinus jeffreyi. This zone lies at a sufficiently great elevation 

 not to be severely affected by the aridity or humidity of the subjacent 

 valleys. It therefore crosses the Sierra Nevada, and is represented 

 on their western slope by a belt of Pinus ponderosa, in its lower part, 

 and another of P.jeffreyi in its upper part. 



Between timber-line and the upper limit of the Transition zone is 

 another zone characterized in the desert by forests of Pinus flexili 'a and 

 P. aristata and known as the Boreal zone. In none of the mountains 

 between the southern Sierra Nevada and the Colorado River does a true 

 timber-line appear, but northward the White Mountains of Nevada, and 

 southward the San Bernardino Mountains, extend above this limit. An 

 abnormal condition of affairs exists on the Panamint Mountains, in the 

 absence of any tree taking the place of Pinus ponderosa scopulorum, 

 which finds its western limit in the Charleston Mountains. The nut 

 pines, not having any forests above them with which to compete, grow 

 to an unusually high altitude, and Pinus flexilis and P. aristata unusually 

 low; so that the Transition zone appears, from the absence of its most 

 conspicuous characteristic tree, to be squeezed out entirely, although 

 it is still marked by the presence of Juniperus occidentals and Cerco- 

 carpus Icdifolius. 



At the time of examination of the desert mountains, the Transition 



•Merriani, North American Fauna, No. 5, p. 24 (1891). 



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