ARABLE WEEDS. ASSOCIATION WITH CROPS 173 

 WEEDS THAT ARE MORE FREQUENT IN CEREAL CROPS. 



wheat or are relatively scarce among barley. The two groups, 

 however, are largely identical, indicating that some factor is 

 at work with one crop that is absent from the other. This 

 factor is probably the difference in the time of sowing of the 

 two crops. Wheat in this country is usually sown in the 

 autumn, thus hindering an effective cleaning of the land. 

 Weed seeds germinate and grow up with the corn, and the 

 nature of the crop hinders an effective clearance by later 

 cultivation. Barley, on the other hand, is spring sown, very 

 often after roots. The land is ploughed up and lies fallow 

 throughout the winter, when the weed seeds germinate and 

 make good headway. Further cultivation occurs before the 

 crop is sown, the weed seedlings are destroyed, and even 

 though other dormant seeds may start into growth they have 

 to face far greater competition from the crop, which gets 

 away rapidly and is a much greater competitor to the young 

 seedlings than is the wheat plant to those weeds that germinate 

 in autumn. If all these weeds are cut out, very few are left 

 which show any special connection with particular cereals. 

 In the following table the two groups are put together in so 

 far as they are identical, and the remaining weeds are classified 

 under their separate headings. It may be noted that while 

 spurry (Spergula arvensis] and fat hen (Chenopodium album) 

 are both discouraged by wheat, the former is specially prevalent 

 among oats and the latter among barley. 



