THE WEEDS OF CULTIVATION 



growth is stopped and the crop is poor. A weed that is often 

 found in great quantities along the edge of a Bean-field is the 

 Gromwell (Lithospermum arvense). This plant grows about a foot 

 high, and is covered, as the majority of the Boraginacese are, 

 with hairs. The flowers are small and white, and the nut-like 

 fruits very hard. 



The number of weeds found in cultivated land is said to be 

 about 280. Of these, only about 100 

 are found above the limit of Wheat 

 cultivation, i.e. above 500 feet in the 

 Highlands. Many of the species which 

 belong to the Wheat zone cease to be 

 prominent above the Wheat line, and 

 become casuals. If seed grain from 

 another district is used, weeds are 

 often imported with it, and may, 

 under these circumstances, spread 

 from a lower to a higher altitude, 

 holding their own for a time, but 

 they cannot stand the stress of com- 

 petition and soon die out. Light, 

 calcareous soils are apt to be more 

 weedy than clay, or sandy, soils. 



The only classification of weeds of 

 arable land that can be given in the 

 present state of our knowledge is 

 based on soils ; for, as has been 

 already said, the only way of ascer- 

 taining whether there is a relation 

 between the crop and the weeds 

 would be by having experimental plots, planted year after 

 year with the same crop, to which the same kind of manure 

 was given season after season. It is, indeed, possible to give 

 the weeds belonging to the Wheat zone ; but it must be re- 

 membered that this includes at least two or three crops in 

 addition to Wheat. 



The following lists are not meant to be mutually exclusive ; 

 some weeds, such as Groundsel, Shepherd's Needle, and Chickweed 



FlG. 41. Corn Gromwell (Litho- 

 spermum arvense}. 



