DICOTYLEDONOUS PLANTS 233 



X. CENTAUREA, L. 



Herbs. Leaves entire or cut, often spiny-toothed. Heads 

 single ; involucre ovoid or globose (Fig. 22) ; bracts closely 

 overlapping, entire, dry and membranaceous. Corollas all 

 tubular, oblique or 2-lipped, inflated above ; the outer ones 

 usually larger and neutral, the inner flowers perfect ; lobes 5, 

 slender. Akenes flattened. Pappus hairs short, slender, rough. 



1. C. Cyanus, L. BACHELOR'S BUTTON. Stem erect, slender, 

 grooved, 1-2 ft. high, somewhat branched. Leaves acute, sessile, 

 narrow, entire or few-lobed. Peduncles covered with cottony wool. 

 Heads -1 in. in diameter, cobwebby. Ray-like flowers few, large, 

 bright blue or pink ; those of the disk smaller. Cultivated from 

 Europe and escaped from gardens. 



XI. CIRSIUM, Tourn. 



Biennial or perennial; stem erect, simple or branched. 

 Leaves alternate, prickly, often forming wings on the stem. 

 Heads discoid, terminal and solitary or corymbed, many-flow- 

 ered; bracts overlapping in many series, the outer shorter, 

 usually spine-pointed ; receptacle bristly. Corollas purplish 

 or nearly white, the tube slender, deeply 5-cleft. Akenes 

 oblong, 4-angled, smooth or ribbed. Pappus of numerous 

 simple or plumose bristles.* 



1. C. altissimum, Spreng. TALL THISTLE. Perennial or bien- 

 nial ; stem stout, very leafy, downy or woolly, branched 4-10 ft. 

 high ; leaves rough-downy above, hoary beneath, fringed with fine 

 prickles, not forming wings on the stem, the lower petioled and 

 often pinnately cut, the upper sessile and entire. Heads ovoid, 1 in. 

 in diameter ; bracts viscid, webby when young, all except the inner 

 ones tipped with weak and spreading bristles. Flowers light purple. 

 Common in fields, woods, and waste places.* 



2. C. horridulum, Michx. YELLOW THISTLE. Biennial or peren- 

 nial ; stem erect, stout, woolly when young, becoming smooth, often 

 purple, branched 1-3 ft. high. Leaves pinnately cut, with very 

 spiny teeth, mostly sessile and clasping, smooth and green on both 

 sides. Heads large, surrounded by a whorl of linear-oblong, comb- 

 like leaves ; involucral bracts linear, ciliate, not spine-tipped. Flowers 

 purple or yellowish. On sandy soil E. and S.* 



