ABOUT THE OAKS OF THE UNITED STATES. 408 
on young shoots, sinuate-angled ; ni are usually 1-1} or even 2 inches long, but on vigorous ground-shoots have been 
found 24 and 3 inches in length by 3 width. The young leaves are densely covered with a rusty, me scurf of 
articulated hair, which after a month or so disappears, leaving a glossy surface. Vernation imbricate ; youngest leaves 
t with recurved margins. Aments about 1} inches long with stellate-canescent rhachis, 5 oval i calyx 
lobes, and a few (mostly only 2-3) small cuspidate anthers. — ree or usually short peduncled, single or in twos ; 
cup very shallow, about 6 lines wide, with ovate-triangular obtuse scales ; gland ovate or subglobose, 5 or 6 lines long, 
covered by the cup for } or } of its length. — Q. myrtifolia, Willd, Wate Pursh, Elliott, only the first two of whom 
seem to have seen sterile specimens ; flower and fruit had been silbeantehccs: Q- Phellos, var. areneria, Chapm. Q. 
aquatica, 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 [398 (14)] 
difference 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 propagate the individual pecul- 
iarities of the parent; “come true,” as the nurserymen express it. For how many generations this 
may continue, and whether in time forms approaching one or the other parent may not appear, 
remains to be seen. At the same time it is a remarkable fact, that, notwithstanding their fertility, 
they do not seem to propagate 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 provisions of nature to keep the species distinct; or, as Dr. Gray suggests, 
fertilization by one of the parents may soon extinguish the hybrid characters. I find ten forms, 
enumerated below, which I consider as real hybrids ; of them only a few, often only single individu- 
als, have become known. Their existence cannot well, without straining facts, be considered due to 
innate variability in the supposed parents. When more carefully looked for, undoubtedly more will 
be discovered. 
White-oaks and black-oaks are too distinct to be crossed. 
Among the white-oaks hybrids seem to be much rarer than among the black-oaks, or it may be 
that they are more difficult to discover. Of the former, I have thus far been able to trace 3 forms 
only which I must take for hybrids, and all of them point to Q. a/ba as one of the parents. 
@. ALBA X MACROCARPA is sent by M. S. Bebb (No. 27) from Northern Illinois; the leaf is that of alba, with a 
persisting down on the under side ; the cup is not larger than in alba, but a little deeper and with the prominent trian- 
n the muddy banks of the Mississippi near this city, 
among them which will illustrate the different sexual qualities 
which hybrids may possess. The first, an offspring of palus- 
tre and sinuwatum, is a normal hybrid with small anthers and 
abortive, shrivelled pollen-grains, with unimpregnable though 
a tly” ae formed ovules, and small and absolutely 
8. perennial like sinwatum, and erect like 
pw oddest flowers of intermediate size, in long, vir- 
rod 
fertile, so that it might be questionable whether it really is a 
hybrid ; and indeed it has all along been considered a form of 
obtusum until Mr 
acter, The trae obtusum is always 
(branches not more than 6 inches long), has minute whitish 
flowers, petals only half as long as sepals, small orbicular 
rsepees and oe suberect pods on very short pedicels. 
ustre is , has large oblong anthers and shorter 
ns loge pods. cross oecurs in all forms, 
and es to the a and erect one, often 
as if tude between a decumbent habit, 
with some branches in one, gh tees in adi: direction ; the 
yellow petals are longer than in obtwswm but much smaller 
than i in palustre, anthers as in the former ; pods shorter than 
in obtusum, on longer, patulous pedicels. 
