174 GEOLOGICAL RELATIONS OF PLANTS. [AugUSt, 



in the neighbourhood. A. Adiantum-nigrum, though found, is 

 much less abundant. 



On the Ivy, both on the chffs and walls, I had the great plea- 

 sure of finding Orobanche Hederce, etc. 



M. H. Wilkin. 



Eampstead, London. 



GEOLOGICAL EELATIONS OE PLANTS. 



An Attempt to Classify the Flowering Plants and Ferns of Britain 



according to their Geognosfic Relations. By J. G. Baker. 



I. Fundamental Generalities. 



1. In regulatings the distribution of species and modifying 

 specific types, the subjacent geological formations, principally by 

 reason of their mechanical properties, exercise an influence 

 which, taken as a whole, is secondary only to that of climate, 

 which it modifies and by which it is modified perpetually. 



2. With reference to the facility with which they jdeld to dis- 

 integration, and to their hygroscopicity and porosity, strata are 

 essentially separable into two principal classes — dysgeogenous and 

 eugeogenous. 



3. Dysgeogenous formations are those which are disintegrated 

 with difficulty, and yield only a feeble detritus. On a grand scale 

 they absorb moisture readily, and furnish stations characterized 

 by their comparative dryness. Rocks of this class mostly contain 

 a large proportion of carbonate of lime in their composition. 



4. Eugeogenous formations are those which abrade easily and 

 furnish an abundant superficial detritus, which may be either of 

 a sandy or a clayey nature. They are comparatively imperme- 

 able and consequently hygroscopic upon a grand scale, furnishing 

 damper stations than the rocks of the opposite category, espe- 

 cially when the detritus is clayey. 



5. Every species possesses essentially its characteristic special 

 range of lithological adaptability, in the same way that each pos- 

 sesses its characteristic special range of climatic adaptability. 

 Under equal climatic conditions some species are restricted to 

 more or less distinctly marked dysgeogenous situations, and 

 others to more or less distinctly marked eugeogenous situations ; 

 but a greater number can adapt themselves more or less deci- 

 dedly to stations of either class. 



