206 VEGETATION OF THE PEAK DISTRICT [CH. 



Limestone. Oats are apparently less responsive to soil factors, 

 and are grown on all classes of soils. On any given soil, the 

 dividing line between the wheat and the no-wheat zone repre- 

 sents a limit determined by climatic conditions ; and this limit 

 varies on the different soils. 



The prevailing views with regard to the climatic factors 

 determining the successful limits of wheat cultivation are given 

 in the paper on the vegetation of the Leeds and Halifax district 

 (Smith and Moss, 1903 : 395—8). It is there stated, chiefly on 

 the authority of Buchan (1862), that wheat requires an average 

 summer temperature of at least 56° F. (13° C.) and a rainfall of 

 not more than about 33 inches (84 cm.). Judging by the 

 present distribution of wheat cultivation in Somerset and in 

 the present district, it would appear that whilst the above 

 figures are approximately correct as regards temperature, the 

 rainfall figures are too low by about ten inches (25 cm.) ; for 

 wheat regularly ripens in Somerset (see Moss, 1907 a or h) and 

 in the Peak District, where the mean annual rainfall is over 

 40 inches (102 cm.). 



Previous British vegetation maps have indicated the culti- 

 vated land by various tints of yellow, irrespective of the 

 proportion of arable land to permanent pasture. On future 

 maps, it is proposed to make some distinction between cultivated 

 land with a high proportion of permanent pasture, as in the 

 Peak District, and cultivated land with a low proportion of 

 permanent pasture, as in East Anglia; and the maps which 

 accompany the present volume are coloured on this plan. 



It has previously been pointed out (Smith and Moss, 1903 : 

 399; Moss, 1907 a: 61) that the limit of wheat cultivation 

 corresponds roughly with the limits of a number of weeds and 

 aquatic plants. The following is a list of weeds which have 

 been noted in the arable fields of the district ; but it should 

 be borne in mind that, as there is but little typical wheat land 

 in the Peak District, the weeds of the wheat zone are, with 

 regard to the district as a whole, either very local or very 

 rare : — 



