COMPOSITAE — THISTLE FAMILY — COCKLEBUR 769 



from Nova Scotia to North Carolina, southwest to Texas and west through 

 Colorado, Utah and Nevada, and north to Saskatchewan and Manitoba. Most 

 abundantly developed in the Mississippi Valley region from Minnesota to Texas. 

 Poisonous properties. The injury from this plant probably comes largely 

 from its mechanical action. As the involucre is indigestible, its barbs some- 

 times injure an animal feeding upon it. Stock will probably not eat very much 

 of it, but on account of the hooked awns of the involucre the animal may have 

 considerable difficulty in removing them. The hairs of the plant cause itching. 

 Several cases of poisoning of hogs, probably due to this plant, have been re- 

 ported to me. The plant contains the poisonous glucoside xanthostrumarin 

 which resembles datiscin. On heating, the odor of succinic acid is given off. 

 According to Chesnut, the young seedlings of three species of cockle bur, among 

 them our Canadian cockle bur {Xanthium canadense) are poisonous to hogs. 

 Dr. Bitting was unable to find a poisonous substance in the growing plants. He 

 thinks the injurious properties are largely mechanical. 



Fig. 446. Cockle-bur {Xanthium canadense). 

 Cause of mechanical injuries to animals. 

 (Dewey, U. S. Dept. Agrl.) 



A writer in the American Agriculturist says: 



When the seed is ripe the bristles are very hard and sharp, and in the stomach and ia 

 testines of the animal, mat or felt together by the aid of their barbs, forming large balls, which 



