VUI. 
PAPERS ON AMERICAN OAKS. 
I. ABOUT THE OAKS OF THE UNITED STATES. 
FroM THE TRANSACTIONS OF THE St. Louis ACADEMY OF ScrencE, Vol. III. 1876-1877. 
WE have quite a large number of oaks in the United States, which for more than a [372 (1)] 
hundred years have attracted the attention of botanists, and we thought we knew them 
_ pretty well, i.e. we thought we could distinguish, limit, and group the species. That may have 
been so, to a great extent, in the old States; but when the Rocky Mountains came to be explored, 
and the regions west of them, new forms were discovered, and often on single specimens, and not 
rarely on imperfect. ones, species were founded and incompletely described, so that now a straight, 
clear path through such intricacies is difficult to find. 
A striking example of the deceptive polymorphism of these western oaks is furnished by the 
common Rocky Mountain scrub-oak. This interesting species grows on the foot-hills of the eastern 
slope of the mountains of Colorado, sparingly near Denver, scarcely north of that city, but abun- 
dantly southward, about the Pike’s Peak region, and thence extends through New Mexico eastward 
into Texas, and westward through Utah and Arizona into Southern California. The centre of dis- 
tribution perhaps, at all events the classical locality of this species, is the mountains above Cafion 
City, in Southern Colorado. 
In the valley and on the mountain slopes about this place the oak thickets abound, 6-8 feet 
high, single trees occasionally 4 or 6 inches thick, and rising up to 12 or 15 feet, rarely higher. 
The leaves are 3-4 inches long, broadly obovate, deeply lobed, sometimes pinnatifid, 
underneath stellate-pubescent ; the broad lobes obtuse or retuse, often again 2-3-lobed. [373 (2)] 
They bear middle-sized or small oval acorns, in more or less knobby, hemispherical cups. 
Scattered copses of these broad-leaved oaks, often of a beautiful brownish-purple in September, 
accompany us to within a few hundred yards of the top of the cafion, but here the character of 
these shrubs changes: the bushes are lower, the leaves smaller and in outline narrower, the lobes 
* narrower and mostly undivided, but still obtuse. Now we near the precipice itself; from the ragged, 
dizzy edge we here and there get a glimpse of the young Arkansas, whose clear, green waters toss 
and foam twelve or fifteen hundred feet under us, through the inaccessible gorge, rushing toward 
the plains. The oak bushes accompany us even here, but now they are only 4-6 feet high, with 
leaves 2 inches long, ovate-lanceolate in outline, no longer lobed, but coarsely dentate, the acute 
teeth terminating in a sharp point: the acorns are scarcely different from those noticed before. A 
few steps more, and we have reached the brink of the precipice itself ; oak bushes here too, but only 
3 or 4 feet high, with small (1 inch long), oval, firm, almost cartilaginous, semipersistent, spiny- 
toothed leaves, here and there with only very few teeth or quite entire; the acorns proportionately 
smaller, of the same short oval shape, or often elongated from an unusually small, scarcely knobby, 
and sometimes peduncled cup. 
