132 BOTANICAL GAZETTE | AUGUST 
notwithstanding the fact that there are many cosmopolitan 
species. A very useful instance is furnished by the genus 
Spirostachys, of which S. occidentalis is the North American 
form, occurring throughout the salt steppes of the Lower 
Sonoran zone; and S. vaginata.and S. Patagonica, two nearly 
related South American species from the Argentine salt steppes, 
where they are abundant and conspicuous. I am inclined to 
believe there is no recent connection between the species 
of these two regions. AHeterostachys Ritteriana merits mention 
here, because, aside from Spirostachys, the other nearly related 
genera are in the central Asiatic salt steppes and Australia; and 
the plant further illustrates the phenomenon of Gulf zone and 
southern Brazil distribution, being described from Central 
America, northern South America, the West Indies, southern 
Brazil, and Argentine.‘ 
ZYGOPHYLLACE. 
The critical work done by Professor Engler on this family ™° 
makes it of special value for our purpose. He has shown that 
there is a very considerable development of the Zygophyllacee 
in the New World, of which the larger portion form the consist- 
ent group Guajacinee, which is the present expression of a 
branching off from Old World Zygophyllacee in geological 
times. With few exceptions the Zygophyllacee in the western 
hemisphere are limited to the Lower Sonoran zone in North 
America and its corresponding zone in Argentine and Chili. i” 
regions in addition are savannas of Venezuela and Colombia, 
southern Florida, West Indies, and southern Brazil; exactly the 
previously mentioned Gulf zone distribution.*? Following is a 
tabular arrangement of the Zygophyllacez, based upon Professor 
Engler’s study of the family : 
5 See under Malvacez. 
*°Pflanzenfamilien 34:74; Geog. Verbr. der Zygoph. im Verh. zu Syst. Glied. 
Abh, Kon. Preuss. Acad. Wiss. zu Berlin, 1896. 
7 Compare Prosopis, Heterostachys, and references under Malvace. 
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