16 ENGELMANN—OAKS OF THE UNITED STATES. [387 
green shrub from 1^-2, usually 4-5, and up to 8 feet high. Leaves 
rounded ovate, cordate, obtuse, or sometimes acute at base, obtuse and in 
youth bristle-pointed at tip, revolute on the margin, thick and leathery, 
persisting 15-18 months. Leaves vary sometimes to broadly obovate, or 
are rarely, in young shoots, sinuate-angled; they are usually i-i£ or even 
2 inches long, but in vigorous ground shoots have been found 2^ and 3 
inches in length by 2 in width. The young leaves are densely covered 
with a rusty, clammy scurf of articulated hair, which after a month or so 
disappears, leaving a glossy surface. Vernation imbricate; youngestleaves 
flat with recurved margins. Aments about inches long with stellate- 
canescent rhachis, 5 oval pubescent calyx lobes, and a few (mostly only 
2-3) small cuspidate anthers. Fruit sessile or usually short peduncled, 
single or in twos; cup very shallow, about 6 lines wide, with ovate-trian¬ 
gular obtuse scales; gland ovate or subglobose, 5 or 6 lines long, covered 
by the cup for J or i of its length.— J$>. myrtifolia , Willd., Nuttall, Pursh, 
Elliott, only the first two of which seem to have seen sterile specimens; 
<^. Phellos var. arenaria , Chapm.; aquatiea var. myrtifolia , A. DC. 
Hybrid Oaks. 
The question of hybridity in plants is in every case difficult to 
solve where its usual character, the sterility of the hybrid, fails 
us, and where we have nothing to rely on but the rarity and indi¬ 
viduality of a form that seems to stand intermediate between two 
well established species which occur in its neighborhood, and 
which could be considered its parents. 
This is just the case in oaks. All the supposed hybrids are 
abundantly fertile, and those of their acorns which have been 
tested have well germinated; in fact, as far as I know, no differ¬ 
ence in fertility or germinating power between them and the 
acknowledged species has been discovered. The seedlings of 
such questionable individuals do not seem to revert to a supposed 
parent, a sport of which they might be claimed to be, but propa¬ 
gate the individual peculiarities of the parent; “ come true,” as 
the nurserymen express it. At the same time, it is a remarkable 
fact, that, notwithstanding their fertility, they do not seem to pro¬ 
pagate in their native woods ; we may properly ascribe this to a 
lesser degree of vitality in the hybrid progeny, which causes them 
to be crowded out in the struggle for existence: one of the pro¬ 
visions of nature to keep the species distinct. 
White-oaks and Black-oaks are too distinct to hybridize with 
one another. Thus far no hybrids have been discovered among 
