506 X. GENEBAL REMARKS. 



whicli are not separated by limitary lines, as the climatal 

 zones are supposed or feigned to be, but which amalga- 

 mate and intermingle one with another. The actual areas 

 and sites of the various species, as well as the direction 

 of increase or decrease in abundance, appear on the whole 

 to accord so closely with existing climatal and other 

 physical conditions, as legitimately to warrant a con- 

 clusion, that the x>Tesent distribution of plants within this 

 country is mainly determined by its present physical cir- 

 cumstances. 



It is therefore contended, that there is no necessity to 

 invent supjoositious explanations about the present geo- 

 graphical positions of the species in this country, under 

 the notion that it is still determined by the conditions 

 and occurrences of myriads of years ago. In existing 

 diversities of climate and local conditions, we find abun- 

 dant circumstances to account for diversities of distribu- 

 tion. Equally so, in existing similarities of climate and 

 local conditions, may be found ample circumstances to 

 account for similarities of distribution. And in each case 

 the transition from similarity to diversity, and conversely, 

 is so very gradual, that any such invented explanations, 

 which presuppose a hard division of the flora into half-a- 

 dozen clearly distinct groups, may fairly be held to arise 

 from a misconception of the true character of the geo- 

 graphic or distributive types. 



The past history of the species individually considered, 

 their comparative ages, and their original introduction to 

 (or inchoation in) Britain, are subjects fairly open to the 

 investigation of botanists and geologists. Such subjects 

 do not appear to be necessarily beyond the scope of hu- 

 man inquiry or successful research ; although hitherto 

 the speculations on them have proved so futile, and un- 

 productive of little else than misconception and misrepre- 



