THE YUCCEAE. 123 
of moisture, and their leaves are well guarded against 
undue transpiration. Like other arboreous Liliaceae, their 
larger representatives produce the impression of being the 
culmination of a vegetative type perhaps formerly of wide 
distribution, but now barely able to hold its own except 
in desert regions where competition between plants is 
less than elsewhere, while structural adaptation enables 
them to endure the rigors of this last resort,—in a 
sense, therefore, recalling the bald cypress ( Taxodium) 
among conifers, which for similar reasons has betaken 
itself to the other extreme of deep swamps. I know of no 
ecological explanation of the filiferous shedding of the leaf- 
margins of many species. 
The dissemination arrangements of the Yucceae are of 
the more highly specialized types. Many species, consti- 
tuting the genus Hesperaloe, Hesperoyucca, and the capsular 
section of Yucca, are wind-disseminated, with thin flat 
seeds lifted from time to time out of the suberect capsules 
by gusts of wind. In Clistoyucca the indehiscent mature 
fruit is spongy and light and apparently adapted to being 
blown about by the desert winds after the manner of blad- 
der-fruits or tumble-weeds. Yucca gloriosa and Y. recur- 
vifolia possess fruits which do not dehisce, though their 
seeds are thin and flat; nor do they become edible in ripen- 
ing, but dry to a firm almost wooden consistency, 
out of harmony with any usual mode of dissemination. 
All of the baccate species of Yucca and the two species of 
Samuela have fleshy edible fruits at maturity, and their 
abundant endosperm suggests an adaptation to the dry 
regions, in which all of them, so far as known, live, with 
the exception of Y. aloifolia, and, perhaps, Y. elephantipes. 
That they have been derived from thin-seeded capsular 
species seems more probable than the reverse, and the 
coreless fruit of the seaside Y. aloifolia suggests its 
independent fruit specialization rather than a genetic con- 
