ABOUT THE OAKS OF THE UNITED STATES. 393 
liarity that the branchlets which had flowered the previous year, and are now maturing the fruit, 
often in the second year do not elongate or make new leaves or new wood, — in short, do not perform 
any function but the maturation of the fruit. In this case the fruit is found near the end of the 
branchlet, absolutely as if it were an annual fruit; but the appearance of the leaves as well as of 
the epidermis of the branch proves them to be over a year old, and wherever a new shoot of the 
present year can be discovered, the difference between this and those of the last year easily solves 
any doubts. In Q. chrysolepis this peculiarity is quite striking ; very rarely (at least in the herbarium 
specimens examined by me) the fruit-bearing branchlets elongate and again bear flowers, which is 
the rule in our deciduous biennial oaks. 
The cup of the acorn, an involucral organ, is in all our species covered with imbricated scales, 
appendicular organs which simulate bud-scales, and even occasionally seem to assume a pseudo- 
phyllotactic arrangement. In the black-oaks these scales are membranaceous and never thickened 
at base; in the white-oaks, on the contrary, they sometimes have herbaceous tips and, at least the 
outer and lower ones, are always more or less thickened, inflated, or knobby at base; they are very 
thick, e. g. in Q. alba and lobata, and very slightly thickened in Q. stellata and Garryana ; in Q. macro- 
carpa they are herbaceously tipped. 
The shell of the nut or acorn is thinner in the white-oaks and thicker in the black-oaks ; a much 
more important and striking character is, that in the former its inside is dark, smooth, wid even 
shining, or rarely pubescent, and in the latter densely silky-tomentose, a difference which, I believe, 
is constant. 
Only one of the 6 ovules of the oak-ovary is developed, while the 5 others persist as small but 
distinctly recognizable oval, dark colored, pendulous bodies, outside of the seed-coat,—in the white- 
oaks at the base of the perfect seed, in the black-oaks just below its tip. Only in one of our species, 
Q. chrysolepis, are they intermediate or lateral, in some acorns almost basal, and in others 
scattered over the side from near the base to two-thirds up. DeCandolle has observed the [380 (9)] 
same in the cork-oak of Europe and in some Mexican white-oaks. The black-oaks with 
annual fructification have these ovules always suspended near the tip of the seed, and are in this 
respect undistinguishable from the regularly biennial black-oaks. 
It is well known that in the southeastern live-oak both cotyledons are united into one mass, — 
a singular but isolated fact which has no systematic significance. 
In the foregoing pages I have purposely left aside the very peculiar Californian Q. densiflora, 
which is in every respect different from the other oaks, and thus far the sole representative of a pecu- 
liar group named by DeCandolle Androgyne. In many respects it is more a chestnut than an oak, 
for it has, just like the chestnuts, the same dense-flowered, erect male spikes, 10 stamens to each 
flower, very small anthers on long filiform filaments, with very small pollen-grains (0.017 mm. in 
diam., not much more than half as large as in other oaks), and in the female flowers slender, terete, 
pointed stigmas, grooved above. In place of the spiny involucre of the chestnut our plant has a 
spiny cup, and is thus made an oak and not a chestnut. The maturation is biennial. The shell of 
the nut is thicker and harder than in any other of our oaks, the inside thickly tomentose, and the 
abortive ovules are found near the top of the seed. The wood is brittle and worthless. 
It results from these investigations that our oaks, leaving again aside the one last mentioned, 
arrange themselves into two great groups, often alluded to above as the white-oaks and the black- 
oaks. 
The white-oaks are characterized by paler, often scaly, bark, tougher and denser wood, and ses- 
sile or subsessile stigmas, and bear the abortive ovules at the base or rarely on the side of the perfect 
seed. Besides this, the leaves and their lobes or teeth are obtuse, never bristle-pointed, though 
