754 WEED FLORA OF IOWA 



it must have been introduced into Europe following their descrip- 

 tion. In the United States the weed has become quite widely 

 disseminated in recent years. The writer found it abundant in 

 the vicinity of green-houses in the Missouri Botanical Garden in 

 1886, subsequently in 1896 he found it in similar situations in 

 Ames and about 1898 or 1899 in La Crosse, Wisconsin. The writer 

 has observed it at other points but always first in the vicinity of 

 green-houses. This would lead to the assumption that it probably 

 has been disseminated with flower seed. 



Horseweed {Erigero-n canadensis). 



This widely distributed weed is common everywhere in North 

 America and is said to have been introduced in the vicinity of 

 Paris in 1635, although Leunis' Botany states "introduced in 

 Europe in 1500." It is mentioned as one of the most common 

 weeds of Germany and Switzerland by Ratzeburg (1859). Treatises 

 by Gareke, Koch, Ratzeburg and Acloque mention it as a common 

 weed. 



Spiny Ciotbur (Xanthium spmosum). 



According to Kabsch, this weed is said to have been introduced 

 into Germany with wool brought from Hungary. Though it 

 originated in tropical America it has become established as far 

 north as Maine (Robinson and Pernald). Thurber in 1859 gave 

 its distribution from Massachusetts to Georgia. In 1889, it reached 

 Leavenworth, Kansas, and in the course of time will be found in 

 Iowa. 



Hawkweed (Senecio vernalis). 



This weed was first mentioned by Rosenberg as occurring in 

 Switzerland in 1882. It spread to Silesia; disappeared; was re- 

 ported in West Prussia in 1824, in Breslau, 1835, Brandenburg, 

 1850, Stettin in 1860, first as a mere waif, then spread to cultivated 

 fields generally. 



Chicory (Cichorium intyhus). 



Chicory was introduced into Dorchester, Massachusetts, in 1775. 

 Torrey records it for the northern and middle states in 1826. Gray 

 in 1848 stated "naturalized in the Atlantic States;" the 6th edition 

 of Gray's Manual stated that it occurs from New England to Iowa 

 and Minnesota; the 7th edition adds Newfoundland and southward. 

 It was common in Wisconsin in 1884 and was spreading; it oc- 



