DESCRIPTIONS OF SOME COMMON WEEDS 



235 



produces slender running rootstocks. It is common in 

 dry soil, especially in the Rocky Mountain country. 



White-leaved Franseria (Franseria discolor. Nutt.). 

 An erect, slender perennial from a few inches to a 

 foot in height; creeping roots; lower surface of leaves 

 canescently tomentose ; upper surface green and smooth, 

 interruptedly pinnatifid, oblong in outline, large, the 

 lower six inches long, lobes usu- 

 ally broad and short; sterile ra- 

 cemes solitary; fruiting involu- 

 cres two-flowered, canescent, 

 armed with short straight spikes. 

 Common on the plains from 

 Nebraska to Wyoming, Colorado 

 and New Mexico. F. Hookeriana 

 is a diffusely spreading, hispid 

 or hirsute annual ; leaves round- 

 ish, one to three inches broad, 

 bi-pinnatifid the upper pinnatifid ; 

 sterile racemes solitary; fruiting 

 involucre awned with flat and 

 thin straight spikes. From Sas- 

 katchewan to Texas and the 

 Pacific coast. F. tomentosa is one 

 foot high, rather stout, apparently a perennial ; canescent, 

 densely tomentose; leaves white below, cinerous above, 

 pinnately three to five-cleft ; spine of fruiting involucre 

 conical, subulate. Occurs along streams from Kansas to 

 eastern Colorado and southward. 



Cocklebur (Xanthium canadense, Mill.). A coarse, 

 rough annual from one to three feet high, with alternate, 

 cordate or ovate, three-nerved, long-petioled leaves; 

 staminate and pistillate flowers borne on different heads, 

 the involucre of the staminate flowers somewhat flattish 

 of separate scales ; receptacles cylindrical ; scales of in- 

 volucre of fertile flowers closed in fruit, two-beaked, con- 



Fig. 148. Small ragweed 

 (Ambrosia artemisiaefolia) 

 (C. M. King.) 



