184 PRINCIPLES OF PLANT CULTUBE 



338. Annual and biennial weeds, since they have a 

 definite life period and multiply almost exclusively by 

 seed, may be controlled by preventing seedage. To ac- 

 complish this with certainty, the plants should be de- 

 stroyed before bloom, as many species possess enough 

 reserve food to mature seeds sufficiently for germination, 

 if cut while in flower. 



339. Perennial weeds often multiply by suckers as 

 well as by seeds (Fig. 83). Since the roots or under- 

 ground stems whence the suckers grow (114) are hidden 

 beneath the soil and are often extremely tenacious of life, 

 weeds of this class are frequently very hard to eradicate. 

 Persistent prevention of leafage, which starves the roots, 

 is always effectual, though it is often very difficult to carry 

 out since the suckers of some species grow with great 

 rapidity. Yet, on the whole, no better remedy is known. 

 Frequent plowing and cultivation of the infested ground 

 is usually the most effectual means of preventing leaf- 

 age. 



Certain very tenacious perennial weeds, as the Can- 

 ada thistle (Cirsium arvejise) and the creeping sow thistle 

 (Sonchus arvensis), when growing on deep, rich loams in 

 which the roots spread freely below the plow line, may, 

 it is said, be crowded out by seeding the land to grass, 

 at less cost than they can be subdued by the plow. 



If we have mastered the foregoing chapters, we are 

 now prepared to enter upon a more advanced stage of 

 culture, and to learn how to cause new plants to grow, 

 and how to treat the plants thus grown that they may 

 best serve our purpose. 



The following books are recommended for reading 

 in connection with the preceding chapter : Elementary 



