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MANUAL OF POISONOUS PLANTS 



Fig. 455. Woolly Thistle (Cirsium canescens). 1, Head; 5, Flower and pappus; 6, 

 Achene; 7, Anthers and style cut open; 8, Pollen grain; a, end of style. (Charlotte M. King). 



About 200 species of the north temperate regions. Some of them are culti- 

 vated for ornamental purposes; many of the species are pleasantly scented; 

 many of them are troublesome weeds. Cnicin C OQ H O 10 has been found in a 

 related genus (Cnicus benedictus). Horses are fond of the heads of many 

 species like C. eriocephalum, C. Drummondii, C. undulatus and others that occur 

 on the Rocky Mountains. None of the species are probably poisonous but many 

 of them have irritating properties. The Canada thistle is used in domestic 

 practice. 



Cirsium arvense (L.) Hoffm. Scop. Canada Thistle 



Smooth perennial herbs, spreading by creeping rootstocks, 1-3 feet high, 

 corymbosely branched at the top ; stem smooth ; leaves lanceolate, sessile and 

 deeply pinnatifid, lobes and margins of leaf with spiny teeth; heads small, 4-1 

 in. high; bracts appressed, the outer with a broad base, inner narrow, all with 

 an acute tip, never spiny ; flowers purple, dioecious ; in staminate plant, flowers 

 exserted with abortive pistil; in pistillate, less so, scarcely exceeding the bracts; 

 long stamens with abortive anthers, tube of the corolla 6 lines long, anther tips 

 acute, filaments minutely pubescent, all of the bristles of the pappus plumose. 



Distribution. The Canada thistle is found in waste places from Newfound- 

 land, Nova Scotia, various provinces of Ontario, to New York, Virginia, south- 

 west to Missouri and Kansas, Colorado to Idaho, Montana and Oregon. 



Cirsium lanceolatum (L,.) Hill. Bull Thistle 



Branching biennial, 3-4 feet high, tomentose, becoming dark green and 

 villous or hirsute with age, branchlets bearing large heads; leaves lanceolate, 



