10 



BULLETIN UNITED STATES GEOLOGICAL SUKVEY. [Vol.Yl, 



Olnci/a Tcsota, Gray. 

 Parkinsonia Torrci/ana, Watson. 

 Prosopis juliflora, DC. 

 Prosopis pubcsccns, BeiitU. 

 Acacia (!ity<iii, Gray. 

 Pru n us Fen nsylvan ica f L. 

 Certooarpus icdi/olius, Nutt 

 Pyrua sambucifolio, ('ham. & Schl. 

 Cratetgus — oear rirularis, Nutt. 

 A m< la itchier alnifolia, Xutt. 

 0d /' im gigcmteus, Engelm. 



Sumbucus (flailed. Xntt. 

 Arbutus Mcnzicsii, Pursh, var. 

 Fru.rinus unomala, Torr. 

 Frawiitus pistaciafolia, Torr. 

 Fraxinus riridis, Michx., f. 

 Chilopsis maligna, Don. 

 Plata uus Wright ii, Watson. 

 Juglans Calif omica, Watson. 

 Juglans rupestris, Engelm. 

 Quercus Emory i, Torr. 

 (h<, reus hypoleuca, Engelm. 

 (/m mis undulata, Torr. 

 Betula occidentalism Hook. 



Fopulus Fremontii, Watson. 

 Populus monilifcra, Ait. 

 Populus tremuloides, Michx. 

 Fopulus trichocarpa, Torr. & Gray. 

 Juniperus occidentalism flook. 

 Juniperus Californica, Carr. 

 Juniperus Virghniana, L. 

 Juniperus pachyphUca, Torr. 

 Abies concolor, Lincll. 

 Abies subalpina, Engelm. 

 Pseudotsuga Pouglasii, Carr. 

 J'lcra Wngelmannij Engelm. 

 Picea pungens, Engelm. 

 Larix occidentalism Nutt. 

 Finns id ul is, Engelm. 

 Finns flexilis, James. 

 Pinus aristata, Engelm. 



Pinus Chihuah liana, Engelm. 



Finns contorta, var. Murrayana,~Eng. 



Pinus monophylla, Torr. 



Finns ponder osa, Dougl., var. scopu- 

 forum, Engelm. 



Pinus Arizonica, Engelm. 

 Yucca brcri/olia, Engelm. 

 This mere botanical enumeration of about fifty species of trees, or at 

 least arborescent plants, gives no proper idea of the arboreal flora as it 

 presents itself to the view of a botanical traveler. It includes all the 

 trees we know to inhabit any part of a vast tract, extending from the 

 eastern base of the Rocky Mounts the eastern base of the Siena 



Nevada and Cascade range.-, and from the Mexican boundary, in lati- 

 tude 32°j t<> the northern limit of forest, in about latitude 50°. The 

 characters of the flora at the two extremes are most widely different. 

 There is a far greater development of forest in the northern part, but it 

 consists of the fewest species; and to the southern portion an undue 

 appearance of richness Is given to a very scanty sylva — first, by the enu- 

 meration <>l' 80 many species which are only arbuscuhv in their best 

 estate, and an- commonly mere shrubs; second, by including species 

 which belong only or mainly to the Mexican frontier region — to the south- 

 ern pari of Arizona and New Mexico. 



< )f the latter sort are Yucca brrrijolia. the only monocotyledonons arbo- 

 reSCenl species (tree il cannot well be called); the giant Cactus. Ccreus 



giganteus, of the Lower Gila district; Pinus Chi kuahuana and P. Arizonica, 

 winch barely cross the Mexican line: Sapindus marginatum, Arbutus 

 Menziesii, or what seems to be a mere geographical variety of the 

 California!) Madroha, Which is not uncommon in Mexico, and which 

 reaches Southwestern Texas; Fraxinus anomala and F. pistaciafolia, 



