DISPERSION. 301 



entanglement in the woolly coat of animals is much 

 more complete. Similar burrs are produced by 

 Xanthium strumarium, which is not a native plant, 

 but has been introduced by the pertinacious ad- 

 hesion of its fruits to the coats of animals. An 

 allied common tropical species (Xanthium spinosum) 

 has by a similar means spread itself over a wide 

 area, becoming thereby a nuisance in some of its 

 adopted homes. In South Africa it has established 

 itself, by means of the merino sheep, and " extended 

 itself through the sheep-walks of the colony to such 

 a degree, and so endangered the character of the 

 wool through its achenes, that special legislative 

 enactments have been made in regard to its extir- 

 pation, and rigid enforcement of penalties alone has 

 kept it from being a sweeping curse to the wool- 

 producers. In the Orange River Republic, where 

 only until last year (1872) this weed was allowed 

 to revel undisturbed, save where some stray Dutch 

 boer was given less to coffee-drinking and sleep, and 

 more to an intelligent regard for the future of his 

 pasturage, it had so affected the wool of some parts 

 of the country as to make it nearly unremunerative 

 as a staple product. Tardy legislation on the ob- 

 noxious introduction had to be adopted there also." 1 



1 Dr. John Shaw in "Journal of Linnasan Society," xvi. f 

 p. 202. 



