Adapt Methods to Conditions. y;^ 



clay soils with a hard subsoil, the Canada 

 thistle, for instance, can be destroyed by 

 sirr^ply turning the land into pasture, and 

 mowing down the thistles when in blossom, 

 and again at a period considerably later. 

 On other soils of more open texture this 

 mode of destroying thistles would not suc- 

 ceed for a long time, if at all. In some 

 climates a considerable proportion of the 

 seeds of the Canada thistle are fertilized, 

 and will therefore grow ; while in other 

 localities it does not seem very harmful to 

 allow the thistle to be harvested along with 

 the crops in which they ripen, because of 

 the inability of their seeds to grow for lack 

 of proper fertilization. Other kinds of 

 weeds, as sheep sorrel, are almost harmless 

 in certain sections ; whereas in others they 

 become great pests. Where winter wheat 

 or rye is grown extensively, specific meas- 

 ures might be necessary to destroy winter 

 annuals ; wdiereas, if the wheat or the rye 

 were not of much account in the rotation, 

 it would be an easy matter to get rid of this 

 class of weeds by growing spring crops 

 successively for a few years. 



If, therefore, we wish to destroy a par- 

 ticular sort of weed with the least possible 



