38 WEEDS OF FARM LAND 



Sorrel (Rumex acetosd) (Fig. 20) is also provided with a much 

 thickened stem, which, however, grows rather slowly and sends 

 up aerial shoots at frequent intervals, giving the whole plant 

 a clustered appearance. 



(/3) Swollen Stems. In some plants the part of the 

 stem below ground is swollen into a kind of tuber which is 

 reproduced by means of small replicas of itself formed at 

 the base. This is well shown by bulbous buttercup (Ranun- 

 culus bulbosus] (Fig. 21), and a very similar type is found in 

 pignut (Conopodium denudatum). 



(y) By Bulbs and Corms. These are in reality swollen 

 underground stems which are clothed with scale leaves, instead 

 of being merely the swollen bases of the aerial stems as in y5. 

 In bulbs the stem portion is at the base and is much flattened, 

 giving off roots below, and bearing on its upper side a number 

 of more or less fleshy scale leaves arranged one within the other. 

 The flowering shoot is in the middle, and grows up above the 

 soil, but the colourless scale leaves remain below ground. 

 The only well-known farm weeds that have bulbs are wild 

 onion {Allium vineale] (Fig. 34), ramsons (Allium, ursinutri) 

 (Fig. 35), and spiked star of Bethlehem (Ornithogalum pyren- 

 aicum). New bulbs are developed year by year between the 

 scale leaves, arising from the stem portion, and as several may 

 be formed from one bulb the spread of the weed is rapid. 



In corms the stem portion is very solid and occupies most 

 of the space. It is covered with a few thin chaffy scale leaves, 

 quite different from the fleshy scales of the bulb. The general 

 history of development is rather similar, new corms being 

 formed either on top or by the side of the old one, the latter 

 in this case perishing at the end of the year. The autumn 

 crocus (Colchicum autumnale] (Fig. 32) is probably the only 

 common farm weed characterised by this method of re- 

 production. 



(b) By Stems Running along the Surface of the Ground. 

 In such weeds as bent grass (Agrostis stoloniferd), silverweed 

 (Potentilla anserind) (Fig. 41), mouse-ear hawkweed (Hieracium 

 piloselld] (Fig. 22), creeping cinquefoil (Potentilla reptans\ and 

 creeping buttercup (Ranunculus repens} (Fig. 23), long thin 

 stems are thrown out from the parent plants. These run 

 along the surface of the ground, and at intervals develop a 

 tuft of leaves and a number of rootlets. The latter establish 

 themselves in the soil, and when once they have taken hold 

 the young plants are capable of leading an independent 



