WEED MIGRATION 



731 



plants immigrated when little was known about the species of 

 plants. What was said about them by the early botanical writers 

 was often very indefinite. In the second place, many of the early 

 writers did not take pains to leave statistics concerning the intro- 

 duction of the plants. The future records, however, will be more 

 accurate as the adventive plants are being recorded by a host of 

 botanical writers the world over. The notes in such floras as 

 Britton's Manual, Robinson and Fernald-Gray's Manual, Bentham 

 and Hooker's Handbook of the British Flora, Garcke's Flora of 

 Germany, Acloque's Flora of France, Moore's Handbook of the 

 Flora of New South Wales, Arcangeli's Flora of Italy, Baron Fer- 

 dinand von Mueller's Systematic Census of Australian Plants, 

 Grisebach's Flora of the British West Indies, Millspaugh's Flora 

 of Yucatan, Hemsley's Botany of Central America, Urban 's papers 

 on the Flora of the West Indies give more or less detailed infor- 

 mation on introduced weeds. 



Fig. 552. Crabgrass (Digitaria sanguinalis) . A cosmopolitan weed. 



The following weeds are more or less cosmopolitan: crab grass 

 (Digitaria sanguinalis), found in North and South America, Eu- 

 rope, Asia, Africa, Australia and New Zealand; barnyard grass 

 (Echinochloa crusgalli), in Europe, Asia, Africa, North and South 

 America and Australia; green foxtail (Set aria viridis), in Europe, 



