146 



WEEDS OF FARM LAND 



capable of gaining and keeping the upper hand to the detri- 

 ment of the crop amongst which it finds itself. 



Marsh cudweed (Gnaphalium uliginosum] belies its name 

 utterly in its distribution as an arable weed. Far from seeking 

 moist spots in which to flourish it is associated with light 

 sandy soils which are well drained and which seldom have any 

 superfluous water held up in them. This is the only one of 

 this class of weeds which is more frequent and abundant on 

 sandy loam than on sand. It is rarely present in any quantity, 

 but is often scarce, though it was once seen to be sub-dominant 

 at Woburn (Beds). Buckman suggests that it is a good in- 

 dex of damp subsoil. 



D. Weeds Associated with Chalk. 



The weeds that are usually associated with chalk can be 

 divided into three distinct classes according to the degree of 

 preference for chalky soil that they exhibit. 



(a) Plants characteristic of chalk. 



(fr) Plants with a definite preference for chalk, but also oc- 

 curring on all soils. 



(c) Plants with a definite preference for light and sandy 

 soils as well as for chalk. 



(a) Plants Characteristic of Chalk. The true chalk lovers 

 are very few in number, and even they are not strictly confined 

 to the one habitat, though the proportion of occurrences on 

 other types of soil is very small. White mustard (charlock), 

 hardhead, and toadflax are the three outstanding plants in 

 this group, while corn gromwell, wild mignonette and lamb's 

 lettuce are equally characteristic but much less frequently 

 seen. 



TABLE VII. WEEDS CHARACTERISTIC OF CHALKY SOILS. 



