124 MISSOURI BOTANICAL GARDEN. 
nection with the desert species, which possess a firm, 
parchment-like core immediately about the seeds. 
The pollination relations of nearly all of the group are 
among the most peculiar and exclusively restricted thus far 
discovered. Hesperaloe secretes much nectar and appears 
adapted to birds, as are the Cape aloes, to which it bears 
no inconsiderable resemblance in its flowers. The other 
genera are sparingly if at all nectariferous, though all have 
septal glands, which are rather small in Clistoyucca, but 
very large in the others. Yucca aloifolia, again in an 
exceptional way, appears to be freely self-fertile, but self- 
seeding is very unusual with all of the other species of 
this genus, as it appears to be with Hesperoyucca, Clisto- 
yucca and Samuela. These, so far as known, depend for 
their pollination upon small moths belonging to the tineid 
genus Pronuba, of which one species (P. synthetica) is 
known only in connection with the single species of Clisto- 
yucca, one (P. maculata, and its variety aterrima), with 
the single species of Hesperoyucca, and the only other 
known species (.P. yuccasella) accompanies the various 
species of Yucca across the continent and has a known 
north and south range from the great bend of the Mis- 
souri river to central Mexico. These moths are not known 
to feed, in the larval stage, on anything but the developing 
seeds of the plants named; so that the mutual dependence 
of moth upon plant and of plant upon moth appears to be 
absolute, —no doubt, taken in connection with the other 
ecological peculiarities of the yuccoids, a fact of the 
greatest suggestiveness, but the bearing and meaning of 
which has as yet escaped both botanists and entomologists. 
That the flowers were formerly pollinated otherwise appears 
to be indicated by the presence of nectar-glands, which 
now appear to be useless. 
The long perianth tube of Samuela,—a type of struc- 
ture usually connected with pollination by some insect of 
corresponding tongue-length, for which the nectar is thus 
