HOW WEEDS ARE SPREAD 21 



from abroad in seeds used for agricultural purposes 

 (see p. 258). In the Colonies some plants have been 

 introduced from Great Britain, and, having got out of 

 hand, have become serious pests. 



(d) Weeds are Spread in many other Ways. A few 

 examples will suffice, (i) Couch or Twitch is spread 

 by the creeping rootstock 

 (Fig. i, a), or by small 

 pieces of this adhering 

 to farm implements, the 

 wheels of carts, and the 

 boots of workmen, these 

 pieces perhaps falling in 

 a clean field and starting 

 to grow. The Creeping 

 Thistle (Cnicus arvensis) 

 and Bindweed (Convolvulus 

 septum) may also be dis- 

 tributed in this way (Fig. 

 i, c and b). (2) All sorts 

 of weeds are occasionally 

 placed on the dung-heap, 

 to be taken at a later date 

 to the fields, where they 

 may form centres of in- FIG. i. a. Rootstock of Couch (Triti- 



on arrniint of cum reens L>>; b - Rootstock of 



aCCOUnt 



Qreat Bindweed (CVww/t/K/wj J#*K* 



the seeds they contain. M; c. Roots of Creeping Thistle 



J (Cnicus arvensis Hoffm.). All x^. 



(3) Hay-loft and other 



sweepings are frequently a source of trouble, as they 

 contain seeds of many undesirable plants. If they 

 are thrown on the dung-heap, or, as often happens, 

 are used for seeding bare patches, the weed seeds which 

 are present will rapidly manifest their presence. (4) A 

 good example of the manner in which seeds may be 

 spread is that of the 5-acre site at the end of the 



