WEEDS 377 



peculiar topographical feature may render cultivation 

 impracticable, e. g. a steep bank, a moor, copse, or wood, 

 a mountain or fringe of the shore, and here the native 

 plants maintain their footing. 



(a) Cornfield Weeds 



In order to render land suitable for crops, the farmer has 

 not only to destroy the native plants, but to change the 

 habitat as well, and this he does by ploughing, draining, 

 manuring, and the like. On this freshly-made soil his seeds 

 are sown, and in time germinate. Meanwhile the surface is 

 exposed to invasion by the native plants which have escaped 

 destruction. Those with a good dispersal-mechanism, will 

 stand the best chance of spreading ; others with runners, 

 such as the Silverweed, or the quick-growing rhizomes of 

 the Couch-grass, soon make headway. Unless care is taken 

 to eradicate them they will occupy the soil intended for 

 the crops, and, being stronger and sturdier, will gain the 

 mastery. From man's point of view these are ' plants in 

 the wrong place ', and he calls them ' weeds '. 



If, however, we make a collection of the weeds of arable 

 land and examine them, we find that very few are of the 

 same species as the native plants of the district. 



The native plants are mainly perennials, while the weeds, 

 like the plants man cultivates, are for the most part 

 annuals. The ground is prepared for annual crops, and 

 annual weeds find it a favourable soil, and thrive accord- 

 ingly; and as long as man disturbs the ground, perennials 

 have little chance of succeeding. Their opportunity comes 

 when cultivation ceases ; with a more stable soil, the 

 sturdy natives soon invade the land, and the annuals, 

 accustomed to rely on man for a suitable habitat, are 

 succeeded by perennials which have migrated from the 

 adjacent, more natural areas. Soon the land reverts 

 practically to its original state. 



