HABITS OF WEEDS 87 



of this type are annuals and develop either a tap root or a 

 more fibrous root which does not thicken up to any great ex- 

 tent, e.g. charlock, spurge, fat hen, wild radish, nipplewort, 

 corn marigold, corn cockle, groundsel, shepherd's needle, 

 poppy, red dead nettle, corn buttercup, and others. 



In a few perennial plants, as pignut and bulbous buttercup, 

 the same erect habit of growth is adopted, but the base of the 

 stem is considerably swollen and serves as a storehouse of 

 food from year to year. Some of the erect weeds make big 

 plants and have large leaves, and as they grow up with the 

 crop rob it of a good deal of light as well as taking up food 

 and water from the soil. 



(2) Tufted Weeds. These grow close to the ground and 

 often branch considerably, forming a close tuft of leaves and 

 stems that is very characteristic in appearance. Most are 

 annual in duration : lady's mantle, mouse-ear chickweed, 

 swine cress and annual meadow grass are the most familiar 

 examples. In some situations the three former have a tendency 

 to send out longer branches, so that this group merges into 

 the next. Spurry, annual knawel, mayweed, and chamomile 

 also grow near the ground and branch repeatedly, and may 

 be included in this section. 



(3) Weeds with Stems Trailing over the Surface of the 

 Ground, but not Rooting at the Nodes. Some of the most 

 troublesome annual weeds come into this section, and given 

 favourable circumstances a single plant is able to cover a large 

 area of ground Each weed possesses a single main root, and 

 sends out horizontal branches which again branch repeatedly 

 until at length a dense mat is formed which effectually covers 

 the surface of the soil and prevents the ingress of light and air. 

 A single plant of orache seen in the summer of 1918 at Hel- 

 mingham in Suffolk measured over 4 feet in diameter, and it 

 needs little imagination to realise that no other vegetation, 

 whether weed or crop, had any opportunity of flowering within 

 the area covered by this plant The trailing weeds are very 

 troublesome among roots, as they tend to cluster round the 

 young plants and are not removed by hoeing, so that unless 

 they are carefully taken out by handweeding the crop has 

 little chance, for root crops are very impatient of overcrowding, 

 particularly in the earlier stages. Knotgrass, -chickweed, 

 speedwells of various species, orache, pimpernel, and wild pansy 

 are plentiful on arable land, and several kinds of trailing 

 geraniums occur as \veeds on leys, where they are harmful 



