462 



Weeds and Their Suppression. 



more than once, and portions of the same field on which hoeing 

 had been stopped by continued rains. The results were very 

 striking ; in many cases the moderately weeded areas carried 

 from 40 to 50 per cent, more crop than those on which the weeds 

 were unchecked. 



Many weeds, such as bindweed and cleavers, pull down cereals 

 or assist in their downfall, and render harvesting difficult and 

 expensive. 



Others harbour or favour the development of insect pests, 

 as charlock does the turnip " fly " ; or act as temporary hosts for 

 rusts, mildews and other parasitic fungi which subsequently 

 spread to cultivated crops. 



Moreover, the pecuniary value of samples of cereals is reduced 

 by the presence of cockle, garlic, cleavers and vetches, and 

 similar reduction in market value of hay and other farm produce 

 is brought about by certain weeds or their seeds. 



Several weeds taint the milk of cows which have fed upon them, 

 and some are poisonous to stock, perhaps the most objectionable 

 in this respect being meadow saffron and water hemlock. 



Before we can hope to deal intelligently with the suppression 

 of weeds it is essential, among other things, that we should have 

 a clear conception of the way in which weeds obtain access to 

 the farm and the methods by which they are spread among 

 cultivated crops. 



The manner in which the seeds of plants are distributed is 

 very varied. The commonest natural process to which the 

 farmer should pay most attention is the distribution effected by 

 means of the wind. The seeds of some of the commonest weeds 

 are, like those of the poppy, so small and light that they are 

 readily blown away from the parent plant. In other cases, 

 such as the thistles, groundsel, dock, and many sorts of inferior 

 grasses, the seeds have special parachute-like apparatus, or 

 other arrangement, of fluffy hairs and flattened wing-like pro- 

 jections, by which they are rendered buoyant, and easily carried 

 about in a light breeze. 



In addition to these natural methods of distribution, weeds 

 •are, very frequently, more or less directly sown over the land 

 or brought on to the farm in inferior hay, or in farmyard manure 

 •and stable dung. Screenings from threshing machines sweepings 



