364 FOREST TREES OF THE PACIFIC SLOPE. 



170) — a most distinctive character — and containing from about 10 to 20 small, 

 smooth, hard seeds (fig. 170). Wood, pale yellowish brown and otherwise 

 similar in its qualities, including weight, to that of the succeeding species. 



Longevity. — Age limits not determined. Trees from 6 to 8 inches in diameter 

 are approximately from 50 to 75 years old, while the larger trees found occa- 

 sionally are estimated to be from 100 to 150 years old- 



RANGE. 



Western Texas (valley of Rio Grande, from Devils River to El Paso) ; west through 

 New Mexico, Arizona, southern borders of Utah and Nevada to California (arid region 

 Of Colorado basin to San Diego County I ; northern Mexico. 



OCCURRENCE. 



Desert river bottoms, waterholes, and canyons; in dry sandy, loamy, or gravelly soils. 

 Forms close and open, often nearly pure stands, but frequently with mesquite. 



Climatic Conditions. — Similar to those of hackberry (Celtis reticulata)- 



Tolerance. — Endures very little shade at any stage. 



Reproduction. — Very abundant seeder. Large quantities of pods infested by grubs. 

 Seedlings sparse in exposed places, but frequent in sheltered canyon bottoms and valleys 

 where seeds have been well covered by washed soil. 



Mesquite. 

 Prosopis juliflora glandulosa " (Torr.) Sargent. 



DISTINGUISHING CHARACTERISTICS. 



The shrub and tree commonly called " mesquite,'* which ranges from eastern 

 Texas to Utah and Colorado and southwestward into southern California. Lower 



enough in the description to unmistakably point to the screwpod mesquite as the plant 

 for wbich the name Prosopis odorata was intended, and there is absolutely no doubt that 

 the fruit figured is of this tree. By all past and present usages among just authors 

 there is every reason for and great justice to Torrey and Fremont in taking up their 

 name and only the most trivial pretext for preceding it by a later name. Prosopis 

 juliflora DC, with which it was confounded, in part, by these authors, had long pre- 

 viously (1825) been published, so that whatever of Torrey and Fremont's description 

 applies to that tree is synonymous. There still remains the incontrovertible fact that 

 these authors' plate, at least, contains separate and distinct figures belonging unmis- 

 takably, the fruit to the screwpod mesquite. and the flower" and foliage to the common 

 mesquite. The very common and unassailable practice ot all taxonomists, in dealing 

 with composite species of this type, is to maintain the name given for the plant which 

 was new when the author dealt with the plants ; while in a case where one name has 

 been applied to two plants new at the time, the usage is to apply the name given to one 

 of these plants and to rename the other. One recent case of this kind is of interest 

 here. Betula occidentalis Hooker includes, in part, a birch native of northwestern 

 Washington and southwestern British Columbia, and the red barked birch of a more 

 eastern range. Only lately it was discovered that these two species were really 

 included. Betula occidentalis Hooker was. therefore, at once taken for the northwestern 

 tree, because the first part of Hooker's description applied to that tree, the latter part 

 to the red barked birch, to which a new name, Betula fontinalis Sargent, was very prop- 

 erly given. The fact that the description was divided gives no more support for this 

 procedure than is afforded in the case of the plate of Prosopis odorata T. and F., the 

 figures of which are distinctly separated, and in reality present a simpler case, because 

 the plant of one figure has already been named Prosopis juliflora DC. The possible 

 argument against maintaining P. odorata T. and F. because it must be cited as a synonym, 

 in part, of P. juliflora DC, applies equally well, if need be, against maintaining Betula 

 occidentalis Hooker, which must also be cited as a synonym, in part, of B. fontinalis 

 Sargent. 



The writer's act in thus disposing of composite species is believed to rest firmly upon 

 the universal law of priority which does full justice to every discoverer. 



"This variety is Torrey's Prosopis glandulosa (1828) supposed by him to be a distinct 

 species, one of the characters of which given being the minute glands (dots) at the base 

 of the main leaf stem and its forks: characters now known to be present on the leaves 

 of all species of Prosopis. In relating this tree as a variety to Prosopis juliflora DC, 

 Torrey's specific name must of course be retained, although it refers to an indistinc- 

 tive character. 



