58o WEEDS : GENERAL 



Rhizomatous weeds possess creeping underground stems or 

 rhizomes, from which arise shoots which come above ground. 

 They are perennials and among the worst weeds of the farm. 

 Well-known examples are couch-grass, corn-thistle, lesser bind- 

 weed and coltsfoot. Some weeds, such as lesser bindweed and 

 climbing buckwheat, have weak stems, but are able to wind round 

 and raise themselves by means of supports. They are termed 

 twining weeds, and frequently do damage to corn and other crops 

 by twining round them in such a manner as to prevent the proper 

 development and exposure of their leaves to the light and air. 

 Of somewhat similar habit are climbing weeds: these possess 

 weak stems, but are furnished with hooks or tendrils, by means of 

 which they cling to plants in their neighbourhood. Examples 

 are seen in cleavers and wild tares. As there are no practicable 

 means of suppressing these plants when they are fully attached 

 to crops, they must be attacked in the early stages of develop- 

 ment. Weeds with strong tap roots descending vertically, or 

 deep-rooted weeds, constitute another fairly distinct group, repre- 

 sentatives of which are wild carrot, ragwort, burdock, and 

 some species of dock and thistle. Most biennials are of this 

 nature. 



5. How Weeds are Spread. — («) Most weeds obtain a hold 

 on the land by being sown in the form of seeds. All weeds 

 are capable of producing seeds if allowed to do so, although 

 those, of annual^ or biennial duration are worst in this re- 

 spect. The seeds may fall to the ground close to where they 

 are grown ; nearly all plants, however, have means of distri- 

 buting their seeds to some distance from where they are ripened. 

 In some instances the seeds are shot out with considerable 

 force by means of peculiar mechanical arrangements of the 

 parts of the seed-cases. A very large number are carried about 

 by the wind. Small seeds, such as those of poppy, are light 

 enough to be blown away, and many which are round roll along 

 the ground easily ; others, such as those of dandelion, groundsel 



