280 NOTES ON THE GENUS YUCCA, 
dug up from the often hard and stony soil of West Texas the different species accessible to him. 
He informed me that Y. angustifolia usually exhibits a perpendicular rootstock of a finger’s thick- 
ness, and two or three feet long, “rising from” (it is evident from what is stated above, that it is 
rather “descending to”) a long horizontal simple or branching part, one or one and a half inches 
thick, exhibiting many knobs and buds of future shoots. Y. rupicola has a rootstock consisting of 
a few thick, cylindric, horizontal branches, one to two feet long. The tree-like Y. Zreculiana has 
few short, thick, club-shaped, horizontal branches to its rootstock, sometimes only a single, short, and 
very stout knob, which does not seem to readily sprout out. It will be interesting to study these 
conditions in other species in their native localities. 
e rootstock of all the Yuccas is, under the name of “Amole,” an important article in a 
Mexican household, being everywhere used as a substitute for soap, as it is replete with mucilagi- 
nous and saponaceous matter, probably a substance analogous to the saponine of the Saponaria root. 
It is curious to learn that the negroes of the coast of South Carolina repeatedly destroyed Dr. 
Mellichamp’s carefully observed clumps of Yuccas, in order to obtain the saponaceous rootstock. 
How may the knowledge of its quality have reached them? Perhaps from the West Indies. 
TRUNK. . 
The trunk of the Yuccas either remains entirely below the surface, or it takes different degrees 
of development above ground. Heretofore, specific characters were partly based on such differences, 
but we know now that only few species are regularly and always acaulescent (Y. rupicola), while 
others, when in a perfect or flower-bearing state, always have trunks (Y- aloifolia and Y. Treculiana, 
though this species was first described as stemless); a certain number, usually counted as 
acaulescent, under favorable circumstances make short trunks, sometimes of only a few years’ [22] 
duration (Y. jilamentosa, and still more Y. angustifolia), and others, again, among them most 
notably Y. baccata, are absolutely stemless near their northern limits, while the farther south we 
meet them the higher and more tree-like their trunk grows. 
The primary axis of the Yuccas is terminated by the inflorescence, and its apex dies with it. 
The plant is then rejuvenated by lateral buds, either from the same axis or from the subterranean 
pain In the first instance the buds appear about the time of the maturity of the fruit, in the 
nk-bearing forms from the axils of the uppermost, in the stemless ones from those of the lowest 
leaves. A single subterminal bud will soon simulate the direct continuation of the main axis; sev- 
eral buds will produce branches in the trunk-bearing species, while in the stemless ones they will 
give the plant a cespitose appearance. From Dr. Mellichamp’s observations, it seems that the cau- 
lescent Yuccas show certain differences in the place where the bud appears; he noticed the young 
bud of Y. aloifolia, from exactly the uppermost axil, at the base of the inflorescence, while in Y. 
gloriosa it sprung from between the uppermost and the next lower series of leaves. Ina Y. jila- 
mentosa in my garden, I observed several buds in the axils of the highest leaves developed two years 
in succession, so that a short branching trunk was formed, while after the third year the vitality of 
this trunk seems to have died out, and the plant was rejuvenated by shoots from the subterranean 
rootstock. In other forms, which probably belong to the same species, I find only rarely, in very 
vigorous garden specimens, a bud from the uppermost axils, while almost always they branch from 
below the crown of leaves. But observations of this kind, relating to the biology of these plants, 
have been made too seldom to permit yet the deduction of general laws. 
The Yucca trunk has a light fibrous wood, which exhibits distinct marks of concentric arrange- 
ment, so that in an old trunk of Y. 7reculiana, of two and a half feet in diameter, I can count twenty 
layers in a space of two and a half inches, or one and a half lines to the layer; the trunks certainly 
grow in thickness as they get older. Another peculiarity of old Yucca trunks is their thick, corky 
