[Chap. LI SOME FAMILIES OF FLOWERING PLANTS 711 



90 per cent of the weight of the entire plant. The cattlemen and the 

 Indians of the southwest have long used cacti for stock feed, first burn- 

 ing off the spines and prickles. 



The giant sahuaro (Fig. 348) lives 150 to 175 years, although the 

 absence of annual rings makes it impossible to ascertain the age with 



Fig. 348. Giant sahuaro (Carnegia) in the vicinity of Tucson, Arizona. Old 

 specimens are favorite nesting sites of woodpeckers. Photos by A. E. Waller and 

 W. S. Cooper. 



accuracy. It grows only about a foot the first 20 or 25 years, but after 

 that it may increase in height as much as three or four inches each 

 year. Its large flower is white and occurs near the top of the trunk and 

 at the tip of each branch. The fruit is quite succulent and is eagerly 

 devoured by animals. Consequently reproduction of the plant from 

 seed in nature is more nearly the exception rather than the rule. 



The maple family (Aceraceae). The maples (Fig. 349) are favorite 

 shade trees among many people who live in the deciduous forest area. 

 They are especially common in the eastern half of the United States, 

 and like so many of our trees they are known as far back as the Cre- 

 taceous period. Most members of the family are trees, but some are 



