128 BOTANICAL GAZETTE [AUGUST 
defined by the North American distribution of P. juliflora, and 
its occurrence in the Andes, the West Indies, etc., marks those 
zones which enter secondarily into the discussion of distribution 
between extra-tropical North and South America.”° 
STRoMBOCARPA. Six species; P. torquata, P. strombulifera, and 
P. reptans in Argentine; P. heterophylla, P. cinerascens, and FP; 
pubescens in the more arid portions of the Lower Sonoran zone 
(west Texas, Mexico, and westward). Of P. pubescens Dr. 
Merriam™ says: 
This mesquite, commonly known as “screw bean,”’ is widely distributed 
over the deserts of the southwest, usually in company with the preceding 
(P. julifiora). 
While the Sonoran and Argentine species of Prosopis yah 
more nearly related than the wide geographical separation 
would seem to allow, only in the case of P. juliflora does there 
seem to have been ready interchange between the regions. 
The genus is favored for a wide distribution by reason a 
the sugary mesocarp, which makes an article of food for herbiv- 
orous animals, the hard indigestible seed being in this way 
carried in the alimentary canal uninjured, and left with excre- 
ment in favorable situations for germination. This is mee 
especially the case in § Algarobia, and above all in P. julifiora, 
of which Dr. Havard™ says: 
The ripe pod or “ bean” contains more than half its weight of assimilative 
nutritive principles, and is therefore a valuable article of food. The most 
important of these is sugar, in the proportion of 25 to 30 per cent. — 
herbivorous animals, but especially the horse and mule, are fond of sees pod 
and thrive on it. In the field it is a welcome though imperfect substitute for 
, ’ d 
grain. The mesquit “bean” is one of the staple foods of Mexicans an 
Indians. 
: : l 
These facts would seem sufficient to insure a very genera 
oe : ing in 
distribution. That the Strombocarpa species are not wanting 1 
*° Compare Bulnesia and Heterostachys. 
** Shrubs of the Death Valley Exped. North Amer. Fauna 7: 300. 
2 Report on flora of S. and W. Texas. Proc. U. S. Nat. Mus. 8: 498. 
3 Op. cit. 499. 
