ARABLE WEEDS. ASSOCIATION WITH CROPS 171 



the very conditions it delights in, so that the black bent is able 

 to make good growth before the crop gets too thick, and is then 

 strong enough to grow up with the peas and beans and to 

 maintain its position. 



(b) Weeds Discouraged by Peas and Beans. 



TABLE XVI. WEEDS DISCOURAGED BY PEAS AND BEANS. 



This is not a very well-marked class of plants. With the 

 exception of fumitory (Fumaria officinalis) few of the weeds 

 are very frequent or plentiful, and several of them are ad- 

 versely affected by other crops as well as by peas and beans. 



Hardhead (Centaur ea nigra) and sun spurge (Euphorbia 

 helioscopia) are the most influenced by this crop, as they failed 

 to appear among it on any occasion, though they were well 

 distributed through all other crops. Neither of these weeds 

 is ever dominant, and sun spurge is frequently scarce, so it is 

 easy to understand why they disappear rapidly under unfavour- 

 able circumstances. Silverweed (Potentilla anserina) is nearly 

 as intolerant as the last two described, for it was only twice 

 seen among peas or beans. 



Field scabious (Scabiosa arvensis), bladder campion (Silene 

 inflata) and dandelion (Taraxacum vulgare) have almost as 

 great an objection to root crops as to peas and beans. Although 

 they occur rather frequently they are seldom or never dominant, 

 and dandelion is often scarce. 



Fumitory (Fumaria officinalis) is abundant and frequent. 

 It is an early plant and much of it has died away by June and 

 July, so that quite possibly it is really more abundant than 

 the records show, as the observations made later in the year 



