338 ' Part III. Chapter 4. 
into Mexico (Saccatae, ı3 species, including Loasa triphylla, Peru to Mexico). 
Mentzelia is the genus, however, most conspicuous because of its distribution 
in the two zones under discussion, although quite abundantly distributed else- 
where, and particularly along the intervening Andes‘). These, apparently, 
constitute remnants of a previously widespread development. Perhaps no plant 
is more prominent as an indicator of extreme desert areas than Zarrea mexicana 
ig. 22. Tas sia rediviva Pursh, the bitter-root, spatlum; an acaulescent, fleshy perennial with 
large rose-colored flowers, native of the mountains of California and extremely tenacious of life, 
oot used by Indians as food. After Die natürlichen Pilsiscnfäniien II ıb, p. 60. 
which is abundant and widespread. This genus is represented at the Rio Colo- 
rado by three species which are sharply distinct from each other and from 
Larrea mexicana. The intervening territory between Mexico and South America 
is without a representative of this genus. 
. The critic work done by Professor ENGLER?) on the family Zygophyllaceae 
makes it of —_ value for our purpose. With few exceptions the Zygophyl- 
ı) Brav, W. L.: On the Relation of the Flora of the Lower Sonoran Zone in are America 
to the Flora of the Arid Zones of Chili and Argentine. The Botanical Gazette XXVII: 121. 1898. 
2) ENGLER, A.: Geogr. Verbr. der Sa in Verh. zu Syst. Glied. Abh. Königl. se Akad. 
d, Wiss. zu Berlin, 1896. Brav,. 1. 0: BD: 
