8 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



carried on by man, who may have introduced some more 

 or less cultivated species. 



But certainly before we arrive at the gate of the 

 meadow some most unmitigated pagans will have become 

 prominent objects in the flora. 



Docks, stinging nettles, thistles of many kinds, the 

 greater plantain and all that tribe, may seem very common 

 objects, but they belong to this third class. They are 

 hangers-on of man, and if he and his cattle ceased to help 

 them they would become extinct over large areas after 

 a longer or shorter period of struggle. Some might main- 

 tain their ground until the actual forest overwhelmed 

 them. Probably most would find some wild spot where 

 they could exist unmolested, pending the slow course of 

 evolutionary adaptation. But they would suffer severely. 

 Meanwhile, however, they exist, and can stand a 

 good deal of hard usage. 



One thing, however, there is that these outer pagans 

 cannot stand and that is the plough. They like their 

 roots undisturbed. But when we reach the cornfield an 

 entirely new set of weeds appear, whose characteristic is 

 not only that they can stand the plough but that it seems 

 as essential to their existence as it is to the crops that man 

 plants. 



Let us look more closely at what the cornfield 

 discloses. 



Here man has been in power for generations. For 

 500, perhaps for 2,000 years, that piece of land has borne 

 his crops, and there stands his wheat-crop now. But 

 besides it are at least a dozen other species of plants which 

 the farmer does not want, but which he cannot eradicate. 

 These are the true weeds, the highest examples of the group 

 I am dealing with. In Great Britain there are, at a very 

 low estimate, some fifty species of them, confined to corn- 



