216 BOTANICAL GAZETTE [SEPTEMBER 
With this species is intermixed a considerable proportion of 
Abies concolor, Libocedrus decurrens, Pinus Lambertiana and some 
P. ponderosa Jeffreyt, without zonal differentiation, except that the 
Abies is more abundant and of greater size toward the upper 
limit, at 7,500—8,000 * altitude (2,286—2,438™). 
On each slope of the mountain there is, beneath the Pine or 
Neutral zone, an intermediate, or true Transitional zone. The 
one differs entirely from the other, each possessing plants pecu- 
liar to itself and also representatives of the superior and the 
inferior zones. On the desert side this zone is nearly crowded 
out, and is present only in a narrow strip, between 6,500 and 
7,500* (1,980-2,286™) altitude, along the northern slope of the 
San Bernardino Mountains, and reaching from Bear Valley some 
fifteen miles towards Cajon Pass. It is indicated by an abundant: 
growth of Juniperus Californicus and Cercocarpus ledifolius. It is 
much intruded upon by the plants of the zones above and below 
it, and within its limits may be seen in juxtaposition such incon- 
gruous species as Pinus ponderosa and P. monophylla, Abies con- 
color and Yucca brevifolia. 
Of this transitional character, also, is the belt of Pseudotsuga 
macrocarpa and Pinus Coultert, extending along the cismontane 
flank of the Nevadan Range, at 3,000-4,500" (915-1,370™) 
altitude. The former is more abundant at the northern part of 
the belt, and the latter at the south, where it occupies a position 
similar to that of the closely allied P. Sediana in the foothills of 
central California. To the north Pinus Coulteri is commoner on 
the lower ridges within the P. ponderosa zone. 
The following table shows those genera which, in our terri- 
tory, are found only, in the Nevadan area.” Genera which are 
abundant and widely distributed are in SMALL CAPITALS; those 
local and rare in @falic. 
In this, and in subsequent tables of regional distribution those genera are 
omitted which are represented by endemic species only. Want of space prevents an 
extension of this investigation to the species of such genera as have representatives 10 
more than one area, but its extension to these would be found to reinforce the conclu- 
sions reached. In determining the sources, or geographical affinities, of the elements 
composing the floras of the different areas, regard is had, not to the distribution of the 
genus as a whole, but of the particular species under consideration. 
