166 THE INDIANA WEED BOOK. 



133. CAEDUUS ALTISSIMUS L. Tall Thistle. Roadside Thistle. (B. N. 2.) 

 Stein stout, branched, woolly, leafy to the heads, 3-10 feet high; 



leaves undivided, ovate-oblong or oblong-lanceolate, sessile, densely white 

 woolly beneath, the margins with bristle-pointed teeth or cut-lobes, the 

 lower 8-10 inches long, the upper narrower and smaller. Heads solitary 

 at the ends of the branches, 2 inches wide; outer bracts of the involucre 

 ovate, tipped with short spines and with a more or less prominent 

 glandular spot along its middle, the inner bracts not spine-tipped; flowers 

 light purple or pinkish. Achenes as in the preceding. 



Frequent along roadsides and borders of thickets, pastures, etc., 

 in moist rich soil. July-Oct. Usually taller and less branched than 

 the common thistle. Associated with the tall thistle or growing in 

 similar places is the field thistle (C. discolor Muhl.) having the 

 leaves deeply divided into lanceolate or linear segments, the wool 

 en their under side much thicker and the glands of the involucral 

 scales larger. Both species are easily subdued by deep cutting or 

 repeated mowing. 



The glands on the bracts of these thistles exude a sticky sub- 

 stance which is very attractive to insects and which often serves to 

 entrap and hold them until they perish. On different occasions 

 in September the writer has found many dead flies, ants, harvest- 

 men, small butterflies and small black snout beetles so held.* A 

 large Scarabid beetle (Euphoria sepulchralis Fab.) is also very 

 common at these glands. Though too big -to be captured, it always 

 appears dazed as if intoxicated by the secretion. Here and there on 

 the stems numerous brown plant lice may often be seen, arranged in 

 rows, their beaks deeply inserted in the grooves, their heads always 

 towards the ground or base of the plant. The stem doubtless yields 

 a sweetish sap agreeable to these aphids. In late autumn these tall 

 thistles add a mite of color to many a woodland pasture, blooming 

 as they do long after the more common thistles have ripened their 

 achenes. One clump of these thistles was measured and found to 

 be over 10 feet high, o'er-topping all the iron- weeds and the tallest 

 of the actinomeris with which it grew. 



134. CARDUUS ARVENSIS L. Canada Thistle. Creeping or Cursed Thistle. 



(P. I. 1.) 



Stems slender, grooved, 1-3 feet high, branched above; leaves lance- 

 olate or oblong, green both sides or somewhat downy beneath, sessile, 

 deeply divided into very prickly lobed or toothed segments, the basal 

 leaves 5-8 inches long. Heads small, 1 inch or less broad, very numerous ; 

 male and female heads on separate plants, the former globose, the latter 

 smaller, oblong, bell-shaped with shorter corollas and more conspicuous 

 pappus; outer bracts of involucre ovate, appressed, tipped with short, 



*See "Cnicus discolor as an Insect Trap" in Can. Ent., 1892, 310. 



