ARID LAND PLANTS 415 
mercial use for many years. The continuous utilization of can- 
delilla wax is based in part on distinctive properties not present 
in other materials and in part on its price in relation to other 
similar waxes, such as carnauba (2). The introduction into com- 
merce of any new product from arid land plants will be difficult 
unless such information is known. 
Natural stands of some potentially valuable desert plants, such 
as canaigre and jojoba (Simmondsia chinensis) (3), are not exten- 
sive enough to furnish material for commercial utilization. Other 
species are sufhciently abundant to provide an adequate and 
perpetuating supply only if they are managed on a sustained 
yield basis. For example, excessive harvesting of candelilla plants 
in Mexico without proper provision for regeneration of the plants 
after cutting, has resulted in depletion of natural stands which 
appeared to be inexhaustible (2). 
Means of Improvement 
Cultivation of arid land plants, either for the purpose of sup- 
plementing supplies from natural sources or for furnishing the 
entire supply, offers promise in many cases. Certain species may 
be adapted to low-cost operations, carried on in conjunction with 
water conservation practices where sufficient water is not avail- 
able for crops with high water requirements. The work of various 
public agencies in reseeding deteriorated areas of range land sug- 
gests methods that may be used. Species that can be readily 
adapted to cultivation, such as canaigre, guayule, and plantago 
(1), have definite promise as crops in irrigated areas or in areas 
with marginal supplies of irrigation water. The ability of arid 
land plants to survive under conditions of extreme water stress 
makes it possible to grow them under a much wider range of 
conditions than can be done with other crop plants. 
Any program for developing desert plants for commercial utili- 
zation should also include thorough investigation of the possibil- 
ity of developing superior strains through selection and breeding. 
Substantial improvement in the yield of a desired constituent 
can often be made simply by selecting desirable plants from nat- 
ural populations. Investigations carried on with guayule (7) and 
