572 WEEDS : GENERAL 



which weeds are harmful, the chief among which are stated 

 below. 



a. All weeds take up space which should be occupied by useful 

 plants, and in this way generally reduce the yield which the 

 farmer expects to obtain from his crop. They moreover throw 

 the crop into shade, as well as prevent the access of adequate 

 heat and fresh air for its satisfactory growth. This is sometimes 

 seen even among cereals, where annual weeds are abundant. 

 The effect is that the crop becomes etiolated, the stems of the 

 plants are drawn up and weak, and liable to fall over or " lodge '' 

 at a later date. The tillering of cereals, which is dependent to 

 some extent upon the access of light to the young plant, is also 

 checked. 



The injurious effects due to the prevention of proper access of 

 air, heat, and light by weeds is, however, seen most markedly 

 where they compete with the slow-growing root crops — carrots, 

 mangolds, and swedes — and with some of the most valu- 

 able leguminous fodder plants, such as lucerne and sainfoin. 

 In the latter and many other useful plants germination is slow 

 and protracted, and the seedlings during early life make little 

 progress in stem and leaf development. In a foul seed-bed the 

 plants are rapidly smothered by weeds, and the crops are liable 

 to suffer a check which they may never properly survive. 



In the case of rapid-growing crops, such as rape or vetches, 

 where the leafage of the plants is considerable, weeds are kept in 

 abeyance to some extent. 



The amount of damage done depends upon the habit or 

 manner of growth of the weeds. Some of them, like groundsel, 

 shepherd's-purse, charlock, and poppy, grow upright, straight 

 from the soil. Others creep more on the surface, and with their 

 stems and broad leaves effectually occupy considerable areas 

 which should belong to the crop. To the latter class belong 

 plantains, docks, buttercups of various kinds, and it only re- 

 quires a glance at a single plant of dove's-foot cranesbill in a 



