184 
Colorado and San Juan expeditions, my attention was naturally 
early drawn to trees which are the most conspicuous, and over 
large areas almost the only arborescent elements in the vegeta- 
tion, and I have studied every phase of change from one variety 
into the other. In the Rocky Mountains all are two-leaved; in 
some arid portions of Nevada the tree is dwarfed to half its 
normal size and all the leaves are single. Midway between these 
districts, in southern Utah, may be found thousands of trees in 
which the leaves are half double, half single; and I would ask to 
which species these belong? It is not strange that to one exam- 
ining Pinus edulis in Colorado, then going by rail to Nevada and 
there finding only Pinus monophylla, they should seem distinct ; 
but to one who should travel by day marches from one district 
to the other, seeing the two forms gradually blending, I am sure 
they would be regarded only as geographical varieties. 
I have called the Nevada form depauperate, a term to which 
Sir Joseph Hooker objects, because, as he says, the leaves are 
_not dwarfed; but there are not half as many on the Nevada tree, 
which has generally shrunk to half the size of its eastern cousins, 
and in the dryest places it inhabits is barely more than a bush. 
I may also add that Dr. Engelmann and Dr. Torrey were 
both satisfied of the specific identity of the two forms. This 
Dr. Torrey has put on record in his catalogue of the plants which 
I collected on the Colorado Expedition (‘ Report Upon the Col- 
orado River of the West”), where, under the name ‘‘ Pinus 
edulis, Engelm. (P. Fremontiana, Gord.)’, which is said to be 
“common in all the higher portions of New Mexico,” “‘ var. mono- 
phyllus, Torr.,” is recorded and referred to its habitat in the 
Cerbat Mountains, Arizona. In these circumstances it will per- — 
haps not seem surprising that I adhere to my opinion that the 
two forms are but varieties of one species, and that the geo- 
graphical distribution of these varieties illustrates in an interesting 
manner the influences which have produced the variation. 
A peculiar confusion seems to exist in the minds of botanists 
in reference to the group of small nut-pines which inhabit our 
Western Territories and Northern Mexico, viz.: 2. cembroides, : 
Zucc.; P. edulis, Engelm.; P. monophylla, Torr. and Frem. (P- 
Fremontiana, Endl. not Gordon); and P. Parryana, Englm. 
