20 



WEEDS. 



Essential character. — Receptacle naked. Calyx imbri- 

 cated, swelling at the base. Seed-down simple, sessile. 



The Sonchus arvensis," or the " Corn sow-thistle/' is a 

 frequent weed in damp loams. The root is creeping, fleshy 

 and milky, running deep into the ground, and difficult of ex- 

 tirpation. 



The Sonchus oleraceus," or the common " Sow-thistle," 

 is much more frequent than the former species, and is a very 

 common weed on cultivated lands. Flower stalks downy, 

 imperfectly umbellate. Calyx smooth. Leaves runcinate, 

 toothed. Root annual, spindle-shaped. Herbage smooth, 

 brittle, milky ; very various with respect to luxuriance, and 

 the number of teeth, lobes, or prickles about the edges of its 

 leaves ; their segments, however, are almost always acute and 

 runcinate. Flower stalks axillary and terminal, rather cymose 

 than umbellate, clothed when young with soft, white, dense, 

 cob-web-like deciduous down. Corolla lemon-coloured. 

 Seeds angular, with crenate ribs. 



" Thistles " are easily eradicated by a careful tillage in kill- 

 ing the roots, and by preventing the perfection of the seeds 

 in cutting the stems when the flowers are in blossom. The 

 seeds are numerous, and are easily carried about by the wind, 

 and consequently no plants should be allowed to grow on the 

 hedge-sides and in ditches, for lanes and road sides often pro- 

 duce seeds to infest the adjoining fields. 



14. The "Spear thistle," and the " common field thistle," 

 belong to the genus " Carduus," one of the most extensive 

 in the vegetable kingdom. It belongs to the class and order 

 " Syngenesia polygamia equalis" of Linneus, and the natural 

 order " Cinarocephalse" of Jussieu. 



Generic character. — Calyx common, ventricose, imbricate; 

 scales very numerous, lanceolate, acuminate, spiny. Corolla 

 compound, tubular, uniform. CoroUules hermaphrodite, 

 subequal, reflected ; the proper one monapetalous, infundibili- 

 form ; tube very slender ; border erect, ovate at the base, 

 quinquefid ; divisions linear, equal, one more deeply serrated 

 than the rest. Stamina : filaments five ; capillary very short; 

 anthers cylindrical, tubular, length of the coroilule, five- 



