THE INFLUENCE OF MAN. 329 



or rushy, marshy ground ; (3) Permanent pasture and 

 sheep farms have been produced from oak-forests or pine- 

 woods ; (4) Modern plantations and policies have been 

 formed ; (5) Railway tracks, ballast heaps, and shale 

 heaps have appeared with their own special floras ; 



(6) There are special plants by houses or waysides ; 



(7) Trees and other vegetation have been injured by 

 factory smoke ; (8) Rivers have been polluted and so 

 affected the vegetation on their banks. 



Bej^ond the extremely fertile character of the alluvial 

 meadows and their liability to flood in winter, there is 

 little that can be given here to distinguish them from 

 the ordinary Grass and Ploughlands of the general 

 surface. Both these latter are artificial floras. Selected 

 species of grasses have been long employed, and weeds, 

 so far as possible, have been eradicated. Grass land 

 shows the following characters. Generally the vegeta- 

 tion is excessively close and thick, so that the colour of 

 the soil cannot be seen. It is green all the year round, 

 for though old leaves and haulms die away, a young 

 growth is always ready below. The fibrous roots are 

 excessively numerous and form a thick turf Most of 

 the plants are perennial, and only a very few form any 

 reserve store of food material ; bulbs and fleshy rhizomes 

 are unusual. The wild oat, however (yArrhenathi^uDi), 

 has peculiar little fleshy tubercles or " corms," and Poa 

 bulbosa has also a sort of corm ; but this plant prefers a 

 sandy soil. The grass pastures are often remarkable 

 for the absence of weeds. The leaves of those that 

 do occur, are generally either more or less grass-like, or 

 are finely divided, so that their lobes or divisions are 

 flexible and narrow enough to compete with the 

 grasses. Thus Plantago lanceolata^ Achillea ptannica^ 

 Scabiosa, and the Ox-eye daisy have rather narrow leaves 



