162 VEGETATION OF THE PEAK DISTRICT [CH. VI 
conditions, have directly or indirectly an enormous influence on 
the differential distribution of the flora and vegetation of that 
district. Precisely what this influence is, however, is a matter 
on which the present state of knowledge in physiological botany 
allows no definite statement to be made. 
Clements (1907: 18) opposes the “chemical theory” (cf. 
Schimper, loc. cit.); and even goes so far as to assert that “it 
now appears entirely incorrect to ascribe the presence or absence 
of certain species on limestone soils to the chemical nature of 
the latter.” Without doubt, the “chemical theory” requires 
close investigation by modern plant physiologists; and a re- 
statement of the whole position is urgently needed. However, 
the study of the vegetation of a district like the present, where 
highly calcareous soils occur in close proximity with soils 
extremely poor in lime, where the climatic factors obtaining 
over the two types of soil are identical, where both habitats 
exhibit every transition from wet to dry, and yet where the 
flora and vegetation of the two types of habitat show very 
marked differences, should convince any observer that the 
“chemical theory” is far from being effete. 
Hall and Russell (1911: 54) have recently stated that “soils 
devoid of carbonate of lime are never fertile, because without 
it the plant food of the soil cannot readily be brought into a 
condition available for the plant, and many of the most important 
bacterial actions in the soil are dependent on the presence of a 
base like carbonate of lime.” 
Kraus (1911) has recently published some valuable statistical 
data bearing on the question; and not until more work has 
been performed on these lines will it be possible to reach the 
solution of this intricate and much-debated problem. 
