DESCRIPTIVE MANUAL 



349 



Fig. 203-A. Distribution of Maximilian's Sunflower. 



narrowing at both ends, nearly sessile, entirely or sparingly dentic- 

 ulate ; heads large, Y^A in. high ; short peduncle terminating the 

 simple stem and later appearing in the axils of lower leaves; invo- 

 lucre consisting of rigid bracts about 1% in. long; ray flowers 

 golden yellow, disk flowers brownish, flowering in late summer 

 and early autumn. 



Distribution. — This weed is common in places from Alberta 

 and Manitoba to Texas. In Iowa it is most abundant in the 

 northwestern and western counties, in the alluvial bottoms of 

 Missouri river and on high prairies of Pocahontas, Dickinson, 

 Emmet and Palo Alto counties; also found east in "Worth, Howard 

 and Cerro Gordo counties. 



Extermination. — This perennial weed has the habit of the arti- 

 choke. The more or less thickened underground stems freely prop- 

 agate the plants. Give the field a shallow plowing then drag and 

 expose the roots to the. sun for a few days. This will destroy the 

 most of the plants. If the field is put into corn give thorough cul- 

 tivation and follow corn with a small-grain crop and then clover. 



Boot-jack (Bidens discoidea (T. & G.) Britton). 



Description. — A diffusely branched annual with alternate, di- 

 vided leaves and slender petioles ; leaflets ovate-lanceolate, pointed, 

 coarsely serrate, small heads of yellow flowers surrounded by a 

 double involucre, the outer of 4 bracts; achenes linear, wedge- 

 shaped, smooth or tuberculate, bearing a pair of short, upwardly 

 barbed awns. 



