102 SILVA OF NORTH AMERICA. LEGUMINOS. 
in the subsoil.1. The bark of the trunk is thick, dark reddish brown, and divided by shallow fissures, 
the surface separating into short thick scales. The branchlets are slender, glabrous, or pubescent, at 
first pale yellow-green, and rather darker in their second year, when they are usually more or less zigzag 
and are often marked with minute dark lenticels and irregularly shaped red blotches. The winter-buds 
are obtuse and are covered with acute apiculate dark brown scales. The branches are furnished at the 
axils of the leaves of their first season with short thick spur-like excrescences covered with chafty scales, 
and are usually armed with stout straight terete supraraxillary persistent spmes which vary from half an 
inch to two inches in length, or the branches are sometimes unarmed. The leaves are alternate on the 
branchlets of the year and fascicled in the axils of those of previous years; they have two or rarely four 
pinne, and are glabrous or pubescent, and deciduous. The petiole is terete, two to four inches in length, 
with an abruptly enlarged glandular base, and is furnished at the apex with a minute gland and 
tipped with the slender subulate spinescent rachis. The pinne are from three to six inches long, with 
petioles enlarged and glandular at the base, and terete or slightly winged rachises, each bearing from 
eight to fifteen pairs of oblong or linear entire acute or obtuse and often apiculate rigid leaflets. 
These vary from one to two inches in length and from an eighth to a quarter of an inch in breadth ; 
they are conspicuously reticulate-vemed, strengthened by broad thick midribs, and are sessile or borne 
on short stout glandular petiolules, and are sometimes remote and sometimes placed close together, 
standing in all positions on the rachis, as often in vertical or oblique as in horizontal planes.’ The 
stipules are linear, acute, membranaceous, and deciduous. The flowers, which are a twelfth of an inch 
long, are greenish white and fragrant, and are produced on short pedicels from the axils of minute sca- 
rious deciduous bracts in slender cylindrical spikes which vary from an inch and a half to four inches in 
length ; these are densely or occasionally interruptedly flowered, and are borne on stout peduncles from 
half an inch to three quarters of an inch long, and when the flowers are open appear bright yellow from 
the numbers of largely exserted anthers. The calyx is glabrous and is barely a quarter of the length of 
the narrowly oblong acute petals. These are slightly puberulous or glabrous on the outer surface and 
covered on the inner surface towards the apex with thick white tomentum which appears as a tuft at 
the apex of the flower-bud. The stamens are straight or diverging and twice as long as the corolla, 
the large dark-colored connective of the anther cells bearing a stalked gland. The ovary is shortly 
stipitate and clothed with silky hairs. 
sive crops until the middle of July. The legumes are linear, compressed at first, subterete at maturity, 
The flowers begin to appear in May, and are produced in succes- 
constricted between the seeds, of which there are usually from ten to twenty, straight or faleate, and con- 
tracted at the two ends, the apex being tipped with the straight or recurved remnant of the style; they 
vary from four to nine inches in length and from a quarter of an inch to half an inch in width. The 
outer coat is thin and ligneous, longitudinally veined, and pale yellow or straw-color often marked with 
1 The roots of the Mesquite appear to develop almost indepen- 
dently of the leaves, and often attain an enormous size on plants 
with stems a few inches in height and with only a small quantity 
of foliage. The tap-root, which is the only one of the vertical roots 
that grows to a large size, often descends to a great depth in search 
of water, and does not branch or decrease much in diameter until 
this is reached. The Mesquite is thus enabled to extract an unfail- 
ing supply of water from low strata, and is not dependent on the 
moisture of the subsoil. Its presence and condition afford almost 
certain indications of the depth of the water-level ; when the plant 
attains the size of a tree this will be found within forty or fifty feet 
of the surface, or, when it grows as a thrifty bush, within fifty or 
sixty feet ; when the roots are forced to descend below sixty feet, 
the stems are not more than two or three feet high. Sand heaped 
by the wind about the stems of the plants causes the development 
of secondary vertical roots and branches which hold more sand and 
earth, and gradually form mounds, often of considerable size and 
height, upon which the plants appear to be growing. 
The value of the Mesquite is greatly increased by the remark- 
able development of its roots, which enables it to reach a deep 
water-level and flourish where no other ligneous plant can exist ; 
these roots furnish large quantities of valuable fuel, which is dug 
from the ground or dragged out by oxen in pieces fifteen or twenty 
feet long in regions where no wood of fuel value is produced above 
ground. (Havard, Am. Nat. xviii. 454.) 
The weight of the wood of the root, as shown by the result of 
the tests published in Volume IX. of the 10th Census of the United 
States, is considerably greater than the average weight of many 
specimens taken from trunks grown in different regions, its specific 
gravity being 0.8493. 
2 Havard (J. c. 453) found 63,660 stomata to the square inch on 
the upper surface of the leaflets of Prosopis juliflora, and 143,235 
on the lower surface, as the mean of several observations. 
