l62 



WEEDS OF FARM LAND 



hardly any overlapping, so that a plant which appears under 

 one heading is very seldom found under another. The cereals, 

 however, do not act quite in the same way. As a whole they 

 form an indifferent body of crops, because hardly any weeds 

 are either specially associated with them or usually absent 

 from among them. Some differences are evident between 

 the cereals, weeds that are common among wheat being 

 often scarce among barley, etc., but the division is not so clear 

 as with the other classes of crops. For this reason a considera- 

 tion of the association of weeds with cereals is postponed for 

 a time, because all the chief weeds can be classified under 

 other headings. 



For this purpose arable weeds may be summarised thus : 



(1) Weeds that are found as often among one crop as 

 another. 



(2) (a) Weeds specially associated with root crops. 

 (ft) Weeds discouraged by root crops. 



(3) W ( a ) Weeds specially associated with temporary grass 

 or clover (" seeds "). 



Q9) Weeds specially associated with temporary 

 grass or clover and wheat crops. 



(ft) Weeds discouraged by temporary grass or clover 

 ("seeds"). 



(4) (a) Weeds specially associated with peas and beans. 

 (ft) Weeds discouraged by peas and beans. 



I. Weeds that are Found as often Among one Crop as Another. 



TABLE X. WEEDS THAT ARE FOUND AS OFTEN AMONG ONE CROP AS 



ANOTHER. 



