PLATYSTEMON AND ITS ALLIES. 153 
America, will the same extent of country be found to present 
half the diversities of soil, climate, altitude, etc., which are 
to be found within the limits of the distribution of Platyste- 
mon. Even as to the immediate seaboard extension of its 
range the genus runs through five distinguishable floral 
belts; one marked by Cape Mendocino and Point Reyes; 
another between Point Reyes and Point Pinos at Monterey; 
a third defined by the latter and Point Conception, above 
Santa Barbara; a fourth between the last named headland 
and Point Loma at San Diego; the fifth between that and 
Cape San Quentin. Each of these belts contains its own local 
species in several genera, and is readily definable as a floral 
belt. But, leaving the maritime sections, where Platystemon 
in several species flourishes in the moist sea air, and even 
under the influences of the salt spray, we find others in the 
coast range of mountains subject to copious rains and 
heavy fogs; then again as many more on the climatologically 
distinct region of the great sunny and rather arid, yet fertile 
plains of the interior of California, the plains of the Sacra- 
mento in the northern, and of the San Joaquin and its 
tributaries in the southern. The foothills of the Sierra to the 
westward of the interior plain have again no dearth of Platy- 
stemons. They seem to lack representation on the subalpine 
and alpine heights of the Sierra Nevada, yet occur again in 
quite a multiplicity of species amid the parched deserts of 
Nevada, Southern Utah, and Arizona. 
Antecedently it would seem impossible to one having any 
idea of the extremely distinct floral regions here hinted at, 
that in any genus of flowering plants a type could in the 
lapse of ages disperse itself over all of them and remain a 
specific unit. 
A careful examination of materials that have been brought 
together from all these diverse fields—a study that has in- 
volved laborious weeks and months of time—has brought to 
