ARABLE WEEDS. ASSOCIATION WITH SOILS 137 



This weed is more frequent on grass-land than on ploughed 

 land. 



Swine cress (Senebiera coronof>us] is a characteristic little 

 plant, which is not very often noticed. It often congregates 

 near the gateways of fields, in the cart ruts, instead of scatter- 

 ing evenly over the fields. It is hardly ever dominant or 

 present in great quantity, and is rarely seen on any of the 

 lighter soils. 



Bindweed (Convolvulus arvensis] is one of the commonest 

 of all weeds, so common that it is rather difficult to say that it 

 has any real preference as to soil. It seems evident, however, 

 that it is less happy 'on the lighter types of soil. This is 

 shown by the frequency with which the weed occurs in the 

 different habitats and also by the number of times it pre- 

 dominates on the various soils. It is very often dominant or 

 sub-dominant on clay, heavy and medium loam, and fairly 

 often so on chalk, whereas on the light sandy soils it is less 

 frequently dominant and more often scarce. The abundance 

 of this weed may be gauged by the fact that in one occurrence 

 out of every five it is either dominant or sub-dominant, 

 usually the former. This is largely due to its habit of growth, 

 as the long creeping underground parts defy all efforts to clear 

 them out, especially on the heavy land, and also the aerial 

 stems cling so closely to the crops among which they scramble 

 that when once growth has fairly started it is almost impossible 

 to remove the weed without seriously damaging the crop. 



(2) Plants which do not Occur so Frequently on Chalk. 



(a) With Distinct Preference for the Heavier Soils. 



Coltsfoot (Tussitagofarfara) expresses a most decided pre- 

 ference for heavy soils. The heavier the soil, the more likely 

 is coltsfoot to be present, and as the soil gets lighter, so does 

 the percentage of frequency of this weed decrease. Never- 

 theless, it may be dominant on any type of soil, clay, 

 medium loam, light loam, sand, chalk, or gravel. Considering 

 the frequency with which the plant occurs it is not very often 

 dominant, but this may be largely due to the special attention 

 that farmers pay to its eradication. This same fact may also 

 tend to decrease the frequency with which it is seen on the 

 lighter soils, and to emphasise its universal occurrence on 

 heavy land. The underground parts penetrate the soil so 

 deeply that it is exceedingly difficult to remove them effectively 

 from heavy soil by any of the usual methods of cultivation, 



