WEEDS— PECULIARITIES AND DISTRIBUTION 421 



The question of the distribution and association of weeds 

 is one of great economic importance, though it is only during 

 comparatively recent years that much definite and accurate 

 work has been done in this field. At the present time, whilst 

 a good deal of positive and exact information is available with 

 reference to the weeds of pastures, our knowledge of the weeds 

 of arable land is still fragmentary and more or less disconnected. 



During the last fifty-five years experiments have been 

 carried out at Rothamsted upon permanent pasture land to 

 determine the relations existing between the plants and the soil 

 on which they grow under the influence of various manures ; 

 the growth of different species in competition has been exhaus- 

 tively tested in the course of these experiments. With regard 

 to arable land, whilst much is known about the individuality of 

 different weeds and many references exist as to the soils on 

 which certain plants have been noticed, very little is known 

 about the actual association between the different species on 

 different types of soil in conjunction with various farm crops. 

 Many observers have been at work but hitherto their observa- 

 tions have not been worked up systematically and so tabulated 

 and reduced as to give the information required in a concise 

 form ; consequently our knowledge in this respect is still 

 somewhat indefinite and vague. 



An attempt is therefore now being made to collect definite 

 and precise information as to soils, weeds and crops in different 

 parts of the country. Work is being done during the summer 

 months on soils derived from different geological formations to 

 determine, as far as possible : 



(a) Whether certain weeds are definitely associated with 

 particular types of soil (clay, chalk, sand, etc.) or whether the 

 nature of the soil is immaterial ; 



(b) Whether the association, if it exists, is constant or whether 

 it varies according to the locality, treatment of the soil, etc. 



(c) Whether the geological origin of the soil plays any part 

 or whether the texture of the soil is the determining factor; 



(d) Whether there is any connection between the crops 

 grown and the weeds which accompany them. 



To this end work has already been carried out in Bedford- 

 shire, 1 in the district between Luton and Bedford, where the 



1 W. G. Brenchley, " The Weeds of Arable Land in Relation to the Soils in 

 which they Grow" (I.), Ann. Bot. January 191 1, 



