SS a SR ere ae ENTS 
1898] FLORA OF LOWER SONORAN AND ARID ZONES 135 
W. Indies, S. pee 3 Pi 
N Bak Aescried ie northern Chili-A panei xerophytic Means of distribution 
11, Vis- V. gem- Fruit of four split- 
cainoa wmulata: ting capsules, 
Lower not winged, still 
Calif light enough to 
be carried by 
winds. 
me 
N 
. Chito- C. Mexi- Fruits large and 
hia cana ,: winged, splitting 
Monte- at maturity. 
el 
Ww 
« Sttico- S$. Greg- Woolly carpels. 
des N 
— 
os 
- Pegan- P. Mexi- Like Fagonia. 
um 
The distribution of Fagonia cretica vars., Tribulus, and Kallis- 
treemia‘is similar to that of Frankenia grandifolia, Chorizanthe com- 
missuralis, Oxytheca dendroidea, Lastarriea Chilensis, etc.; that of 
Larrea and Porlieria is like the isolated Frankenias, Spirostachys, 
etc. Larrea may be cited as the best case illustrating that 
Phase of distribution in which there is absolute separation of 
the species both in a geographical and a genetic way. No other 
‘Species are more reliable determinants of zonal areas that those of 
Larrea "8 which is also to say that distribution from one zone to 
another Over thousands of miles in which Larrea could not grow 
'S very improbable, and this is clearly indicated by the distinct- 
ness of the species. Professor Engler expresses the opinion” that 
the present condition of Larrea, and indeed of the Guajacinez, 
**Merriay, North American Fauna 7:293; Engler, Pflanzenfamilien 3*:86. 
° Geogr. Verbr. der Zygophyllacez, etc. Abh. Preuss. Akad. Wiss. —:17. 1896. 
