ARABLE WEEDS. ASSOCIATION WITH SOILS 135 



Corn buttercup {Ranunculus arvensis), though very local 

 in occurrence, is sometimes a bad weed on heavy wheat 

 land, and the heavier the land the more likely is the plant to 

 cause trouble. It is sometimes dominant, and the presence of 

 the seeds in the corn tends to depreciate the value of the 

 wheat considerably as so much more cleaning is necessitated. 

 The weed is far more characteristic of clay and heavy loam 

 than appears from the table, for although it occurs on the 

 other soils as indicated it is usually so scarce that only close 

 observation reveals its presence. Probably in many of these 

 cases it has simply sprung from stray seeds introduced when 

 the crop was sown. 



The inclusion of black bent (Alopecurus agrestis) in this 

 list may perhaps be criticised, as it occurs quite frequently on 

 other soils and is also dominant on them. Nevertheless, the 

 preference for clay and heavy loam is so marked that a point 

 may be stretched to include it among the characteristic heavy 

 land weeds. Black bent is capable of doing much damage 

 among corn crops but happily does not usually occur in any 

 quantity, its habit being such that ordinary methods of rotation 

 farming keep it in check. Occasionally, though, it has been 

 seen dominant on clay, chalk, and medium loam, and, when it 

 does occur, is not often scarce but usually present in ap- 

 preciable amount. 



(b) Plants Common on Heavy Land, but also of General 

 Distribution. Several of the most common and abundant 

 weeds are found distributed over every type of soil, but never- 

 theless they occur more frequently and more plentifully on 

 the heavier soils. The frequency with which the weeds in 

 this class occur is in striking contrast with the scanty distribu- 

 tion of those pla-nts which are really characteristic of the heavy 

 soils. These weeds may be divided into two distinct sections. 



(1) Plants which flourish equally well on chalk. 



(2) Plants which do not occur so plentifully on chalk. 

 (a) With distinct preference for the heavier soiU 

 () Equally plentiful on heavy and medium soils. 



In both cases the lighter loams and sand afford less con- 

 genial habitats. 



