CLASS XIX. ORDER I. 309 



leaves riincinate, upper ones ovate, acuminate, pe- 

 tioled, toothed in the middle. 



This plant differs from the species before described, in having 

 blue flowers. These are rather small and numerous. — Low 

 grounds, rare. — August. — Biennial. 



330. ARCTIUM. 



Arctium lappa. L. Burdock. 



Leaves heart shaped, unarmed, petioled. L. 



No plant is better known than this. Its very large, heart 

 shaped, wavy leaves cover the ground for some extent around it. 

 The stem, which rises three or four feet, is branching, round, 

 furrowed, and rough. Flowers numerous, terminal, purple. 

 This plant intrudes itself on every one's acquaintance by the 

 sharp, firm hooks at the end of the calyx scales, which attach 

 themselves to the clothes, and serve as a remarkable mechanism 

 for dispersing the seeds. — Common in waste and cultivated 

 ground. — July, August. — Perennial. 



331. CNICUS. 

 Cnicus arvensis. Willd. Canada Thistle. 



Leaves sessile, pinnatifid, spinous ; stem panicled ; 

 calyx ovate, its spines minute; down feathery. Sm. 



Syn. Carduxts arvensis. Sm. 

 Serratula arvensis. L. 

 This species is easily distinguished from the rest of our this- 

 tles by its small flowers, and its thornless calyx scales. It com- 

 monly forms beds by its perennial, creeping roots, and is exceed- 

 ingly difficult to extirpate. The stems are two or three feet high, 

 smooth, many flowered. Leaves alternate, sessile, pinnatifid, 

 with numerous lobes, and very thorny. Flowers terminal, pur- 

 ple ; the scales of the calyx ending in a short, weak bristle, rather 

 than a spine. This plant seems to have come to us from the 

 westward, where it is exceedingly troublesome. The name of 

 Cursed thistle has been given it in England. — July, 



