HEDGEROWS 



297 



a 



Indeed, if the land is not properly cleaned, the crop itself 

 is likely to succumb. Root-crops especially are liable 

 to suffer in this way, for they are low-growing, and the 

 weeds can grow up above them into the light and air. 

 But the danger is not so great in a cornfield, for the cereals 

 are quick-growing plants which effectually smother most 

 others, and by the time the ears are ripe there are very 

 few strong, healthy weeds left. The most frequent weeds, 

 therefore, are annuals, which reach maturity early and 

 produce an abundance of seed before the crop is big 

 enough to injure the plants. 

 Perennials are rare in the 

 cornfield, for they not only 

 have little opportunity of 

 forming good seed, but their 

 underground parts are cut 

 up and destroyed by the 

 plough. The only ones which 

 are abundant are those like 

 the false oat (Fig. 115) or the 

 couch-grass, which have sub- 

 terranean stems stored with 

 food. When these are cut 

 up by the plough they are not 

 destroyed, but actually in- 

 creased in numbers, for any 

 one of the little tubers of the 

 false oat, or any portion of 

 the couch-grass rhizome, will 

 give rise to a new individual. 

 We have already seen in 

 Chapter XX. that the true 

 weeds of cultivation i.e., 



those which are found only in ground disturbed by 

 man are aliens ; but many plants of our native flora 

 occur as well. Those which do best as weeds are those 

 with a good mechanism for the dispersal of the fruits 

 or seeds as fast as they are killed off in the field so 

 they arrive again from their natural habitat. The most 

 common of our native weeds are the following, those 

 marked with an asterisk being annuals : *Myosurus 

 minimus (mouse-tail), Ranunculus repens, *J?. parviflorus, 

 *Cardamine hirsuta, *Sisymbrium TJialianum (thale-cress), 



FIG. 115. TUBEROUS STEM OF 

 FALSE OAT-GRASS. 



