1 ] 9 settlers— old and new 



and is now so common in thickly inhabited portions of 

 southern Arizona that one hardly knows whether to call 

 it cultivated, escaped, or adventitious. In any event, a 

 slow-motion movie of the United States since the sixteenth 

 century would show the vegetative as well as the human 

 population ebbing and flowing — ^mostly flowing — in all di- 

 rections. 



Nearly everywhere he goes man intentionally carries 

 with him such directly useful plants and animals as can be 

 persuaded to grow in whatever new country he is coloniz- 

 ing: cattle, sheep, horses, Indian corn, cotton, etc., etc. 

 Sometimes he unknowingly brings animals which had once 

 lived there but subsequently became extinct, as he did 

 when he brought the horse to America. To the southwest- 

 em deserts he brought even the camel, which is said to 

 have survived there as an escapee for forty years or more. 

 The organisms which go along with him as stowaways are 

 far more numerous. Wherever one of his ships lands, rats 

 are pretty sure to go ashore with him. The dandelion fol- 

 lows him into almost every temperate climate, the cock- 

 roach into the tropics and the arctic as well. 



Even today he is far less master of his environment than 

 he likes to imagine. New destructive pests and new diseases 

 make the headlines. No one notices the arrival of other 

 organisms, desirable, undesirable or merely harmless. But 

 they do not ask our permission to come. It is said that most 

 of the earthworms of the northeastern part of the United 

 States were killed during the Ice Age and that most of 

 those now performing their indispensable service to agri- 

 culture in New England are of various European species 

 unwittingly introduced by early colonists in the soil about 

 the roots of imported plants. To find native American 



