448 COMPOSITAE (COMPOSITE FAMILY) 



on the long, naked stalks near 

 their summits ; the many rays 

 long, yellow, notched at their tips, 

 pistillate and fertile ; disk-florets 

 orange-yellow, perfect but ster- 

 ile ; bracts of the involucre nar- 

 rowly ovate with long, stiff 

 points spreading nearly as wide 

 as the rays. The achenes, being 

 the fruit of the ray florets, are 

 in rings around the outer edge 

 of the heads, each about a half- 

 inch long, brown, flat, oval, and 

 broadly winged, deeply notched 

 at the top, without pappus. 

 (Fig. 312.) 



Means of control 



Cultivation of the ground is 

 the best method of suppres- 

 sion ; but if not desirable to 



FIG. 312. Compass Plant (Silphium break up the meadows where 



the plant is most troublesome, 



it should be cut deeply, below the crown, with a sharp hoe or 



spud, before the first flowers mature, the roots being salted so as to 



check new growth. 



PRAIRIE DOCK 



Silphium terebinthinaceum, Jacq. 



Other English names: Rosin Plant, Prairie Burdock. 



Native. Perennial. Propagates by seeds. 



Time of bloom: July to September. 



Seed-time: August to October. 



Range : Ontario and Ohio to Minnesota, southward to Georgia and 



Louisiana. 

 Habitat: Prairies and dry woods, meadows, and pastures. 



Terebinthine is the ancient word for turpentine, and the resin- 

 ous juice of this and the preceding weed accounts for one of their 



