1903] FLORA OF SOUTHERN CALIFORNIA 217 
GENERA FOUND ONLY IN THE NEVADAN AREA. 
Exclusively Nevadan Boreal 
LiBocEDRUS Heracleum Athyrium Sroka agai 
Danthonia srola Woodsia Geu 
Hemicarpha Chimaphila CYSTOPTERIS Ey = 
VERATRUM SARCODE Cryptogramma Circeea 
Tris Rhododendron s Hippurus 
Corallorhiza Brianthus lopecurus Myriophyllum 
CASTANOPSIS Cycladenia lyceria Gentiana 
SPRAGUE Boschniakia Puccinella Polemonium 
Lewista KELLOGGIA Trisetum pu 
Heucher Hemizonella uzu Taraxacum 
Philadelphus Hulsea Smilacina is 
Heterogaura Ratllardella Acteea Hymenopappus 
Sphenosciadium BARBAREA Arnica 
In the first two columns are placed those genera which, as to 
the species by which they are here represented, belong exclus- 
ively to the flora of the Sierra Nevada; in the last two those 
which have a more or less wide distribution throughout the 
whole Boreal province. But it is to be noted that every genus, 
without exception, has for its representatives in our flora the 
identical species which are found in the more northern parts of 
the Sierra Nevada. Moreover, with the exception of eight of 
the Nevadan genera and three of those of wider distribution,” all 
belong in the so-called Neutral or Transition zone. 
From a consideration of this table it is evident that the flora 
of these southern mountains coincides with that of the general 
Sierra Nevada, of which it is physiographically a part. And so 
far as its position in the phytogeography of North America is 
indicated by distinctive genera, the Transition zone is prepon- 
derately Boreal rather than Sonoran. 
THE DESERT AREA. 
The Desert area consists of two very distinct subareas : the 
Mojave subarea, which includes all the country to the north and 
€ast of the San Bernardino and Chuckawalla Mountains ; and the 
Colorado subarea, which consists of the great desert valley 
between the Chuckawalla Mountains and the southern prolonga- 
* Namely: Castanopsis, Philadelphus, Pyrola, Chimaphila, Bryanthus, Cycladenia, 
Boschniakia, Raillardella, ute ium, Woodsia, Crypiogramma. 
