10 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
Parkinsonia microphylla Torr. U.S. Rep. Expl. Miss. Pacif. 4: 82. 1856. 
Type locality, ‘‘ Banks of the Colorado, and on Williams’ river,” Arizona. 
This, the common palo verde, is discussed and illustrated by Doctor Hornaday in 
the ‘“‘Camp-Fires.” Doctor Hornaday speaks of it as follows: } 
“Of all the tree products of the desert the palo verde is one of the most beautiful 
and interesting. Itsname is Spanish and means ‘green tree.’ According to its soil and 
water supply, it may be as large as an adult apple tree—fifteen feet high, with a trunk 
nine inches in diameter—or as small as a mountain laurel bush three feet high. Almost 
as far as it can be seen, you recognize it at once as something different and remark- 
able. Instead of a top that is made up of leaf masses, one laid upon another, you 
see that its foliage—or rather the masses where its foliage ought to be—is composed 
of straight lines, and angles. The palo verde bears a few tiny leaflets, so small that it 
would take about twelve of them to cover a postage stamp; but in November they 
exert no influence whatever upon the general aspect of the tree. 
‘Regardless of leaves, however, from root to top the palo verde is of the most beau- 
tiful green that could be imagined. It is not the bold, waxy, aggressive green of the 
creosote bush, but the soft, smooth, and delicate green of the asparagus. 
“The bark is as smooth as the surface of polished oak, and trunk, branch, and twig 
are alike persistent green. Even the bark of the trunk has a surface like a robin’s egg. 
“The terminal twigs are long, straight, and slender, like masses of green darning 
needles set where the leaves ought to be. The density of their color, added to their 
unique form, gives the tree as a whole a peculiarly lineated top. This is one of the 
very few desert trees that is free from thorns. 
“This tree is not particularly useful. Its chief purpose is to ornament the arroyos 
and flood basins of the desert regions, and to furnish brake blocks for desert freight- 
wagons. It strings along the arroyos, wherever the water supply is a little above the 
average, but on the open, level plains it is rare. Often from many a square mile it is 
quite absent. In density and grain, its wood is much like that of the white birch. 
The trunk consists of a single stem, upon which the branches are set in very abrupt 
and angular fashion, all of which merely adds to the odd appearance of the tree. ” 
Prosopis velutina Wooton, Bull. Torrey Club 25: 456. 1898. 
Type locality, ‘Probably first collected with young fruit in the valley of the Nazas 
in northern (?) Mexico by Gregg.” 
No specimens of this were collected, but it is illustrated in several of the illustrations 
of the ‘‘Camp-Fires.’’ Doctor Hornaday writes of it as follows: 2 
“The honey-pod mesquite is the most persistent bush tree of the deserts. Both in 
form and size it is much like the palo verde, and in southern Arizona and Mexico the 
two species are almost inseparable companions. On the desert plains, where water is 
scarce and dear, the mesquite is a modest little bush three feet high; but along the 
arroyos, the valleys, and in the business centers of the flood basins, where the water 
wagon is more in evidence, it develops into a real tree. Often it grows to a height of 
twenty-five feet, with a writhing trunk twelve or more ‘uches in diameter. In growth 
habit it is very much likean apple tree—a low, heavy, wide-spreading top with crooked 
bra ches that frequently are horizontal, on a short, stout trunk of irregular shape. The 
bark is gray and the foliage is of a pale gray green tint—not so pleasing as the asparagus 
green of the palo verde. * * * Both foliage and ‘“‘beans” are eaten by horses and 
cattle when grass is not obtainable and hunger is great. Its seeds are greedily eaten 
by all the small rodents of the deserts, and by many birds also. Although its leaves 
are very small, the shade of the mesquite is very grateful and comforting. 
‘The mesquite is well provided with thorns, but, fortunately for the proletariat, they 
point forward instead of back. Its wood is hard, fine-grained, durable, and the general 
stand-by for fuel throughout the whole Southwest. Blessed is the desert wayfarer 
' Page 45; see also plate facing p. 70, same work. 2 Page 47. 
