1 66 WEEDS OF FARM LAND 



is less marked with two instances of dominance among roots 

 and twenty-three elsewhere. Coltsfoot (Tussilago farfara) is 

 very considerably affected, but makes a better fight for its 

 position than any other weed in the group, managing to 

 become dominant as often in proportion among roots as 

 among other crops. 



(3) (#) Weeds Specially Associated with Temporary Grass and 

 Clover (" Seeds") or with " Seeds" and Wheat Crops. 



These two classes of weeds are very clearly marked out. 

 Two distinct factors are evident in this case, which work to- 

 gether and help to make the flora of "seeds" crops more 

 distinctive than any other. The first factor is that " seeds " 

 form essentially .a smothering crop. They are sown very 

 thickly, and from an early date they spread out and cover the 

 ground closely, in contrast to the cereals, which grow fairly 

 upright, and to roots, in which open spaces are left for a long 

 period of time. Consequently, any weeds that dislike com- 

 petition stand a poor chance among seeds, and only those can 

 flourish whose habit permits them to enter into effective com- 

 petition with the crop. Some, but not all, of the " seeds " weeds 

 are equally abundant among wheat. The second factor is that 

 the seed of clover, trefoil, medick, etc., is so small that effec- 

 tive cleaning is difficult, and large numbers of weed seeds 

 may therefore be introduced when the crop is sown. These 

 introduced weeds are a class apart, for they flourish among 

 their harbouring crop, but do not persist further on in the 

 rotation in any quantity. Apparently cultivation is obnoxious 

 to them, and the great majority quietly disappear when once 

 the ley is ploughed up. The weeds that are common among 

 both seeds and wheat are also usually introduced with the 

 seed crop, but they seem to be able to hold their ground 

 for a season in the wheat that so commonly follows a clover 

 ley. After this, however, they tend to disappear like the rest. 

 The two sets of weeds are as follows : 



