HEDGEROWS 297 
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 yyg. 115.—TusEnovs Srem oF 
Chapter XX. that the true Fatse Oat-Grass. 
weeds of cultivation —7.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, *R. parviflorus, 
*Cardamine hirsuta, *Sisymbrium Thalianum (thale-cress). 
