464 



WEEDS OF AGRICULTURE. 



THE plants described in the preceding pages are those which 

 form the subject of general cultivation. The weeds of agri- 

 culture are those which grow amongst the cultivated plants, 

 and which it is the province and the duty of the farmer to 

 destroy, and if possible to exterminate. The prevailingplants 

 of this class vary in every country, and in different parts of 

 the same country; and, indeed, the same observation may 

 apply to the different counties. Low. 



Weeds may be divided into two separate or general classes 

 those which propagate themselves by their seeds, and which, 

 having once flowered, perish and those which have perennial 

 roots, and flower and bear seeds for successive years, like that 

 vile pest, the Canada thistle. The first are annual or biennial, 

 according as they require one or two years to complete the 

 period of their vegetation. The second are perennial plants, 

 and grow again from the roots, as well as propagate themselves 

 from their seeds. Ib. 



In the case of annual or biennial weeds, if the stem is de- 

 stroyed at the time of flowering, or just before it, the individual 

 is destroyed, and its further means to propagate the species are 

 taken away; but in the case of perennial weeds, the destruc- 

 tion of the stem does not infer the destruction of the plant, 

 because the plant has the power of propagation from the roots. 

 From this distinction it would seem more easy to destroy an- 

 nual than perennial weeds; yet this conclusion does not always 

 hold, for some of the annual species have such numerous 

 minute seeds, that it is often very difficult to extirpate them; 

 and when they have got into ground, keep possession, even 

 more inveterately than those which have the power of spring- 

 ing again from their roots. Ib. 



Of the perennial weeds, greatly the most troublesome are 

 those which have creeping roots; for these extend themselves 

 below ground, and, if any of the parts of the roots remain, 

 those may give birth to new plants. Either class of weeds 

 may be frequently destroyed by the same means, namely, by 

 assiduous tillage of the ground. Ib. 



