THE OAKS OF THE UNITED STATES. 
By Dr. George Engelmann. 
We have quite a large number of oaks in the United States? 
which for more than a 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 speci¬ 
mens, aftd 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 east¬ 
ern slope of the mountains of Colorado, sparingly near Denver, 
scarcely north of that city, but abundantly 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 distribution perhaps, at 
all events the classical locality of this species, are the mountains 
above Canon City in Southern Colorado. 
In the valley and on the mountain slopes about this place the oak 
thickets abound, 6-8 ft. 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 . 
Missouri botanical Garden 
6EQRSI Engelmann Papers 
8 9 10 Missou 
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