The Weeds of Arable Land. III. 
BY 
WINIFRED E. BRENCHLEY, D.Sc., F.L.S. 
Rothamsted Experimental Station ( Lawes Agricultural Trust). 
I NITIAL investigations carried on in parts of Bedfordshire and the West 
Country 1 have shown that while definite relations exist between the 
weeds and soils of arable lands, these relations are partly local and partly 
general in extent. It is evident that in some cases a weed that is sympto- 
matic of a certain soil in one district is not so exclusively associated with it 
in another, but there are also indications that certain species are sympto- 
matic or characteristic of the same type of soil in different districts. 
Naturally, the ‘ general ’ relations will need more exhaustive proof than the 
f local *, and a true estimate will only emerge gradually as the field of 
investigation is enlarged, since each fresh observation ratifies or discounts 
the previous deductions. 
In the earlier work special care was taken to select districts in which 
drift deposits were conspicuous by their absence, so that the soils dealt with 
might be regarded in the main as derived from the geological formations 
immediately underlying them. In Bedfordshire, Wiltshire, and the Bath 
district large tracts of land exist overlying one particular formation, such as 
Greensand, Chalk, or Gault, so that one can feel some confidence as to the 
origin of the soil. It was found, however, that the geological derivation 
apparently has little to do with determining the weed flora, the texture 
being a far more potent factor. Chalk forms the great exception to this 
rule on account of its very peculiar nature. To verify this still further, 
in 1913 the scene of operations was transferred to Norfolk, where drift soils 
are dominant. Geologists aver that the soils in Norfolk are derived from 
glacial deposits, the supposition being that at two distinct glacial periods the 
country was invested by ice sheets, which on melting left the drift deposits 
known as ‘ North Sea Drift ’ and f Boulder Clay ’. 2 These drift deposits are 
1 Brenchley, W. E. : Weeds of Arable Land. I. Ann. Bot., xxv, No. xcvii, Jan. 1911, 
pp. 155-65. Ibid., II. Ann. Bot., xxvi, No. ci, Jan. 1912, pp. 95-109. 
2 See Harmer, F. W. : The Glacial Deposits of Norfolk and Suffolk. Trans. Norfolk and 
Norwich Naturalists’ Soc., vol. ix, pp. 108-33. 
[Annals of Botany, Vol. XXVII. No. CV. January, 1913d 
