748 WEED FLORA OF IOWA 



near La Crosse. It was abundant in Iowa in 1886, was reported 

 from Eagle Grove in 1894 by Cratty, and by the same observer at 

 lake Okoboji in 1901. The writer observed it abundantly in 

 various places in Nebraska and eastern Colorado in 1894 and gave 

 a more definite account of its distribution and spread in a paper 

 in Proceedings Iowa Academy Sciences. In 1912 it was very 

 abundant everywhere in Iowa. The seeds are easily scattered by 

 the wind, which probably accounts for its wide distribution in a 

 comparatively short time. 



Thistle (Cirsium palustre). 



This European thistle is recorded as naturalized in woods. East 

 Andover, New Hampshire, (Holt) by Robinson and Fernald in the 

 7th edition of Gray's Manual, 1908, and was reported from Iowa 

 in 1911 and again in 1912. 



Canada Thistle (Cirsium arvense). 



This well known weed is common everywhere in Europe and is 

 perhaps a weed of the open. Linnaeus in his Flora Lapponica 

 (1837) notes that it is the greatest pest of our fields. It is dis- 

 tributed from the Atlantic to the Pacific across the northern states 

 and in Canada. In Iowa it is found more particularly in the 

 north half of the state. The earliest floras of the state (Arthur, 

 Bessey, and Parry) note its occurrence in Iowa. It has occurred 

 in Ames for forty years. In 1889 it was noticed in many counties. 

 Cratty reports the species from Emmet county in 1892. At this 

 time it had been reported also from Howard, Adair, Chickasaw, 

 Johnson and Poweshiek counties. In 1899 it was thoroughly es- 

 tablished in a forest near Steamboat Rock in Hardin county. 

 Plants from the early introduction seldom produced seed, but seed 

 from the later introductions is not uncommon ; thus it has been 

 matured in O'Brien county and in Cresco, 1892 (C. V. Johnson). 

 It is spreading rapidly in northern Iowa, having become much 

 more widely distributed in 1903 and 1S06 with clover seed. 



It has been reported from Johnson county, 1874 (0. G. Bab- 

 cock) ; Lawler, 1890 (P. H. Rolfs) ; Greenfield, 1891 (F. C. 

 Stewart) ; Corning, 1895 (A. B. Shaw) ; Taylor, 1895 (J. B. 

 Matthews) ; Maple River Junction, 1895 (L. Bernholtz) ; Farragut, 

 1895 (C. Collman) ; Marcus, 1896 (Willey) ; Winterset, 1896; 

 Barnes City, 1896 (J. W. Jones); Nevada, 1898 (G. C. White); 

 Steamboat Rock, 1899; Rockwell, 1901 (J. H. Boom); Badger, 



