Books and Current Literature. 



91 



not been studied thoroughly enough, as yet, to warrant an 

 opinion as to their identity. The varieties commonly found in 

 the United States are few in number compared with those of 

 other warm regions. Those imported by the Bureau of Plant 

 Industry during the past five years have come from Mexico; 

 the Mediterranean region of Europe, Asia, and Africa; the Ha- 



Fig. 6.— A "spineless" prickly pear of a kind commonly grown in Arizona and 

 California. One-th»rd to one-half of the fruits have been picked off. Reproduced by 

 courtesy of the Bureau of Plant Industry. 



waiian Islands; and from some South American countries. 

 There are forms grown commonly in South Africa and in Aus- 

 tralia and some of the Pacific Islands. It is believed that there 

 are not less than thirty species and varieties, belonging to the 

 two genera Opuntia and Nopalea, which have an agricultural 

 value. The small, technically spineless but spiculated forms, 

 of no economic value, are not considered in this list; only those 

 which are rapid in growth and become large plants are here 

 taken into account. 



