THEVOICEOFTHEDESERT ^Q 



successive horses, it is perfectly possible for a botanical 

 garden to exhibit, alive and growing, the unspecialized 

 ancestor and the most highly speciaHzed desert species 

 as v^ell as many successive stages in between. 



An interesting fact about the family and one which 

 raises other questions is this: it seems to belong ex- 

 clusively to the Western Hemisphere. With the possible 

 exception of one peculiar species which may be native 

 to Africa, all of the perhaps eight hundred kinds of cacti 

 grow naturally only on our side of the world. On the other 

 hand, many, many plant famihes are "cosmopolitan." You 

 may, that is to say, find them growing as natives on several 

 of the widely separated continents. But the cactus, un- 

 less one counts the single dubiously African species, are 

 all American. If they ever grew naturally on any other 

 continent they must have become extinct long ago. 



This is by no means to say that they wont grow any- 

 where else if given a chance. Once they were taken to 

 Africa, to Italy and the Holy Land by the hand of man, 

 they flourished there. So, too, did they flourish in Aus- 

 traha. As a matter of fact, when the prickly pear was 

 incautiously introduced there, it liked conditions so well 

 that it became a disastrous pest. Beheved to have -been 

 introduced in 1839 as one plant in a flowerpot, it began 

 to get out of hand about thirty years later. By 1900 it 

 had taken over some ten million acres; by 1920 it domi- 

 nated sixty million; and it was estimated to be rendering 

 land useless at the rate of a million acres a year. Finally 

 it was brought under control only after large sums and 

 great effort had been expended. 



This should convince the most skeptical that if cacti 



