THE CACTUS FAMILY 



CACTACE^ Lindley 



OME cactuses have been regarded as trees by various authors, but it 

 seems best to us to exclude them all from the category. The stem- 

 structure of big and little ones is very similar, and no criterion, except 

 that of size, is available to determine which to include and which to 

 regard as shrubs or herbs. They form a natural group not readily divisible into 

 herbs, shrubs, and trees, and are very numerous in the arid regions of temper- 

 ate and tropical America. 



Four species, natives of the south central and southwestern United States, 

 have been described as trees. The largest of these is the columnar Suwarro, 

 Cereus giganteus Engelmann, of Arizona, southeastern California, and Sonora, 

 which sometimes reaches a height of 20 meters, with a trunk up to 6 dm. in 

 diameter, either simple or with several upright branches; the stem and branches 

 are longitudinally ribbed and the ribs bear very numerous clusters of stout 

 spines 2 to 4 cm. long. The white flowers are about i dm. long and 6 cm. 

 wide, crowded near the top of the stem. The pulpy fruit is ovoid, red, edible, 

 and about 6 cm. long. 



Three large species of the genus Opuntia inhabit the same general region. 

 These are much branched very prickly plants, the prickles accompanied by 

 minute barbed bristles. All three species have round knobbed stems and 

 branches and attain a maximum height of only about 4 meters. Their flowers 

 are pink, purple, red or yellow, the corolla rotate. 



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