ARABLE WEEDS. ASSOCIATION WITH SOILS 127 



The table also shows how persistently some of the worst 

 weeds, as thistle, knotgrass, black bindweed, and fat hen, 

 maintain their hold upon the ground in spite of the strenuous 

 efforts of the farmer to eradicate them. The creeping 

 thistle masters the situation more frequently than any other 

 weed. No matter what the soil nor how carefully the land is 

 farmed it is almost impossible to get rid of it, and it takes 

 advantage of every opportunity to spread more and more. It 

 occurred on 73 per cent, of the fields examined, and in 125 of 

 these, i.e. II per cent., it was the chief and dominant weed, 

 holding the worst record of all weeds in this respect. 



The curled dock (Rumex crispus) may be dominant on 

 any soil, and it would be rampant everywhere if it were left 

 alone, but so much time and labour has been spent on its 

 eradication that the presence of too many docks in normal 

 times is a sign of bad farming and neglect. It is possible to 

 make a clearance by persistent effort. Fat hen and chickweed 

 are often dominant on various soils, but field speedwell, 

 groundsel, and shepherd's purse less frequently. Most of 

 the other weeds show some preference in their dominance. 

 Black bindweed is frequently the chief weed on the lighter 

 soils, but was never seen dominant on clay or chalk, whereas 

 its close relative knotgrass is dominant on all types of 

 soil, heavy or light, chalky or non-calcareous though it 

 dominates rather more frequently on the lighter than on the 

 heavier soils. Ribwort plantain and shepherd's needle are 

 seldom abundant, but very occasionally they will dominate on 

 chalky soil. The shepherd's needle is curiously local in its 

 distribution. In Bedfordshire, Nottinghamshire and Derby- 

 shire it seems to be absent from chalk, and behaves practically 

 as a calcifuge. In Norfolk it was never seen on chalk and only 

 occasionally on chalky loam, but in the West Country it is 

 most prevalent on chalk and on other soils of very calcareous 

 nature, so that in that area it is chalk-loving instead of calci- 

 fuge. This is probably one of the cases in which competition 

 and local conditions have far more to do with distribution 

 than the nature of the soil, though it is not very usual for such 

 a complete inversion of the habitats to take place. 



Bent grass (Agrostis spp.\ commonly known as twitch or 

 couch, causes much trouble in places. It may be dominant 

 on any type of soil, and indeed in the frequency with which 

 it is the chief weed on a field it takes third place. On the 

 lighter soils it is frequently scuffled out and burnt in heaps, 



