] 23 settlers— old and new 



floras." What lias been happening to them is what hap- 

 pened to such a human community as Tombstone which 

 once flourished, but now survives at all largely because 

 tourist curiosity keeps it alive much as it keeps alive the 

 bison herds and the flocks of wild turkeys now "protected" 

 because people like to see them. 



Such relict floras occur in many parts of the world, but 

 they are especially conspicuous and perhaps especially 

 common in regions like this where only a small margin 

 makes life possible, and where organisms which have 

 achieved very special adaptations to very special condi- 

 tions cannot survive even slight changes. It is just possible 

 that even the giant saguaro which grows nowhere else in 

 the world except within a rather small area may be such 

 a relict flora in an early stage of its coming extinction. I 

 know of no evidence that it once grew much more widely, 

 but it is certainly not reproducing itself at a rate which 

 will maintain its dominance in many of the areas which it 

 now does dominate. And in any event there are other 

 plants which are obviously only lingering in one or more 

 spots isolated by many miles from the only other com- 

 munities of their kind. In many cases it is, for a change, 

 not man but nature herself who is gradually making it im- 

 possible for them to live where they once flourished. Slight 

 changes in temperature, or rainfall, or what-not are prov- 

 ing to be decisive, and we can only guess whether such 

 minor changes in the flora really are only minor or whether 

 they mark the beginnings of a change which, in the course 

 of centuries or millennia, may change the whole face of 

 the country as that of America or Europe has changed re- 

 peatedly during the course of the ages. 



One case happens to interest me especially. In northern 



