290 Part II. Chapter 3. 
It is to be noted that Astephanus, the single northeastern genus peculiar 
to the Colorado Desert, is known from a single collection. All the others 
are southeastern, and all but ten extend into Lower California. On the other 
hand, Canotia and Fallugia, two of the southeastern plants of the Mohave 
Desert are found only in the Providence Mountains, which may prove to be 
included in the Colorado Desert region. Only four of the peculiar Mohavan 
plants have been reported from Lower California. 
Geographic affinities may be exhibited by different species of certain 
genera which are differently represented in each territory, as shown in the 
following table: 
Colorado Desert. Mohave Desert. 
Agave deserti Engelm. Agave utahensis Engelm. 
Aster Orcuttii Aut. Aster tortifolius A. Gray. 
Cassia Covesii A. Gray. Cassia armata Watts. 
Coldenia canescens DC. Coldenia Nuttallii Hook. 
» Palmeri A. Gray. 
Dalea (Parosela) Emoryi A. Gray. Dalea Fremonti Torr. 
» Parıyi T.&G. »  polyadenia Torr. 
»  Schottii Torr. 
»  spinosa A. Gray. 
Gilia bella A. Gray. Gilia dichotoma Benth. 
» Schottii Wats. »  Matthewsii. 
» tenuiflora Benth. »  setosissima A. Gray. 
Lupinus arizonicus Wats. Lupinus brevicaulis Wats. 
Pentstemon ambiguus Torr. Pentstemon glaucus Graham. 
Phacelia micrantha Torr. Phacelia Ivesiana Torr. 
Psathyrotes ramosissima Torr. | Psathyrotes annuus Nutt. 
All the species in the Colorado column have southeastern affınities; all 
those in the Mohave have northeastern affinities. In the former, ten out ” 
sixteen extend into Lower California. The facts already accumulated indicate 
that in the Colorado Desert the Sonoran flora which extends over the entire 
desert area is slightly modified by any other. The Mohave desert flora, 0" 
the contrary, shows a marked influence from the Great Basin flora. The limit 
to which this extends appears to be defined by the Chuckawalla Mountal0® 
The difference in the character of the two floras is only in part due to clima ” 
causes, but is largely influenced by the topography of the region. In the ns 
case, a current of migration was able to pass up, encountering NO pay 
barriers, from Arizona and Lower California into the Colorado Desert; N rt 
other a current from eastern Utah and Nevada entering the Mohave e- 
ann Death Valley, a part of the desert, would meet no considerable obstaci® 
until it reached the San Bernardino Range and its continuation. 
The geographic relationship of the Death Valley flora is clear. 
plants of the valley almost without exception are species which extend 
The arid 
souti- 
