DESCRIPTIVE MANUAL 



377 



Pig. 221A 



Figure 221B 

 Fig. 2 21- A. Trichomes or plant hairs of wood thistle. 

 Fig. 221-B. Distribution of Prairie Thistle. 



purple flowers ; heads 1-1% i n - l° n g ; bracts of the globose involucre 

 somewhat suppressed, slightly arachnoid, lower bracts ovate with a 

 broad base and a weak prickly recurved bristle, slight dorsal gland, 

 inner linear-lanceolate with a nearly colorless entire appendage ; 

 flowers purple, tube of the corolla 11-12 lines long, lobes of the 

 corolla terminating in clavate tips ; anther tips acute, filaments 

 pubescent; bristles of pappus plumose; achene 22 lines long, 

 smooth, upper part yellow. 



Distribution. — Common in many portions of Iowa ; Marshall, 

 Johnson, Winnebago, Lee, Winneshiek, Allamakee, Greene, and 

 Emmet counties ; at Keokuk, Muscatine, Ames, Cedar Rapids, Car- 

 roll, Des Moines, Polk City, Steamboat Rock, Mason City, Belle 

 Plaine and Iowa City. 



Extermination. — This field thistle should be treated like all other 

 biennial weeds. The flattened masses in the spring should be cut 

 off below the ground and none of the plants allowed to go to seed. 

 We have received numerous inquiries in regard to this weed from 

 western and northwestern Iowa. 



Iowa Thistle (Girsium ioiuense (Pammel) Fernald). 



Description. — Biennial with downy, branching stem; leaves 

 roughly hairy above but white-woolly beneath, oblong-ovate to nar- 

 rowly lanceolate, sinuate-toothed, or somewhat pinnatifid, lobes or 



