49. 



prickly wings deeply pinnatifid, the lobes with rigid prickly 

 points, upper face roughened with short hairs, lower face with 

 a cottony tementum ; heads one and three quarters to two inches 

 high, bracts of the involucre lanceolate, rigid when young, more 

 flexible with age, long attenuated prickly pointed spreading tips, 

 arachnoid woolly; flower hermaphrodite, tube of the corolla ten 

 lies long, anther tips acute, filaments pubescent, achenes smooth, 

 one and a half inches long, pappus of numerous plumose bristles. 

 CANADA THISTLE (Cirsium arvense (L.) Scop.) 



A smooth perennial, spreading by creeping roots and root- 

 stocks, one to three 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, three- 

 fourths to an inch high, bracts appressed, the outer with a broad 

 base, inner narrow, all with an acute, never spiny tip ; flowers 

 purple, dioecious, one plant with stamens and the other with 

 pistils. Common in many parts of the state. 



COCKLE BUR (Xanthium canadense Mill.) 



A course, rough annual from one to three feet high, stem 

 marked with brown punctate spots; leaves alternate, cordate or 

 ovate, three nerved, long petioled. Flowers monoecious, stamin- 

 nate and pistillate flowers in different heads, the pistillate clus- 

 tered below. The involucre of the staminate flowers somewhat 

 flattish of separate scales, receptacles cylindrical. Scales of the 

 fertile involucre closed in fruit two beaked, containing two 

 achenes (seeds). The bur is densely prickly and hispid, the 

 achenes are oblong without pappus. At the upper end of the 

 involucre are two large prickles. 



Each bur, as stated above, contains two flowers which develop 

 into the "seeds." The statement is frequently made "that one 

 of these may germinate the first year, and the other lie dormant 

 until a later time. It has been found that if a bur lies in such 

 a position that one seed is up and other down, the one next the 

 soil may germinate while the other remains dormant. This is 

 one reason why the plant is difficult to exterminate. 



GIANT RAGWEED. KiNGHEAD (Ambrosia trifida L.) 



This weed is a stout scabrous, hispid or nearly glabrous an- 

 nual, three to twelve feet high. Leaves all opposite and petioled 

 three nerved, deeply three to five lobed, the lobes are ovate and 

 lanceolate and serrate, the upper leaf sometimes ovate and undiv- 

 ided; flowers monoecious, staminate borne in spikes surrounded 

 by the larger bract-like leaves. The involucre is turbinate to 

 obovoid, five to seven ribbed, beaked, each rib bearing a tubercle 

 near the summit; the involucre enclosing a single oily seed, 



