48 



WEEDS AND USEFUL PLANTS. 



Obs. This is an exceedingly troublesome weed in Europe, and is be- 

 coming so in some portions of this country. It infests those grounds 

 which are best suited to grain-culture ; as the seeds retain their vitality 

 for a long time it is very difficult to eradicate it when once established. 



In this, as in other cases, the plant should be destroyed before the seed 

 is formed ; as sheep are fond of the herbage they are sometimes turned 

 into a field to destroy the crop of Charlock. 



6. ARMOR A' 01 A, Rupp. HORSERADISH. 



[Name from one of the Greek names for Radish.] 



Pod (pouch) elliptical or globose ; the valves turgid, not nerved. 

 Petals white, much longer than the calyx. Seeds numerous. Leaves 

 undivided or the lower ones pinnatifid. 



1. A. ru$tica'na,Rupp. Radical leaves on long petioles, oblong, crenate, 



rarely pinnatifid ; those of the stem lanceolate. 



RUSTIC .ARMORACIA. Horseradish. 



Fr. Moutarde des Capucins. Germ. Der Meer-Rettig. Span. Rabano. 



Root perennial, long, terete, fleshy white, very acrid. Stem 2-3 feet high, angular - 

 striate, smooth, with erect axillary branches. Radical leaves large (8-15 inches long 

 somewhat resembling those of a Dock, or Rumex) ; petioles 4 - 12 inches long. Racemes 

 corymbose, elongating. Petals white. Silicles oval, usually abortive. 



Gardens: margins of ditches, &c. : introduced. Native of Europe. Fl. May -June. 

 Fr. June -July. 



FIG. 21. Field Mustard (Sinapis arvensis), illustrating the general appearance of flowers 

 in this family. 22. An enlarged flower opened to show the unequal stamens. 23. A pod. 



