GEOGRAPHICAL BOTANY AS THE RESULT OF ADAPTATION. 409 



GEOGRAPHICAL BOTANY AS THE RESULT OF ADAPTATION. 

 By Rev. Prof. G. Henslow, M.A., V.M.H., &c. 

 Inteoductiox. 



Geographical Botany, or the study of the existing distribution of 

 plants over the globe, has been a favourite one with many botanists. 

 Linnaeus, in 1750, noticed how groups of plants from various countries 

 often had peculiarities common to many or most of them, and the 

 classification of such groups has been the work of succeeding geographical 

 botanists. 



" The Vegetation of the Globe " was the title of a large work by 

 Grisebach in the seventies, who described vegetation under the headings 

 of Climate, Forms (such, for example, as the uniformly dwarf habit of 

 Arctic plants), the Vegetable Formations of the Tundra, of Forests, 

 Steppes, &c. ; while the study of plant-structure soon showed that it was 

 in correlation with the conditions of life. Thus, Grisebach alludes to the 

 thick cuticle in plants of hot deserts, as well as to their reduction of leaf- 

 surface, &c. To this study Haeckel has now given the name of 

 " Ecology." 



Before the last quarter of the nineteenth century geographical 

 botanists made little or no attempt to explain how such adaptations came 

 about. Thus, speaking of spiny processes, Grisebach observes that certain 

 cases " ought to supply us with the law according to which the most 

 suitable habitat has been assigned to such plants." 



It is now perceived that it is by the universal law of Self-adaptation to 

 the Environment, by means of protoplasmic response to external influences, 

 that the correlations are brought about. Hitherto, therefore, Botanical 

 Geography has been contented with but little more than the accumulation 

 and classification of the materials, so to say. 



For this law we are really indebted to Darwin,* though he unfor- 

 tunately discarded it for his theory of Natural Selection as being " the 

 means " by which vegetable forms were supposed to be selected and 

 survive in the struggle for life. 



We now know that this view was based on unfortunate mistakes, and 

 what I have elsewhere called " the True Darwinism " is the real interpreta- 

 tion of Evolution. This has been proved to be true by an ample amount 

 of induction, as well as an abundance of experimental verification of an 

 exhaustive kind. 



What I propose now doing is to take examples of the different classes 

 of vegetation over the globe, from the Tropics to the Arctic regions, 

 calling attention to prominent instances of adaptation, brought about by 

 the plants themselves, which constitute their generic or other characters. 

 The external conditions which excite plants to adapt themselves to their 



* There were really others before him, as Lamarck ; but I refer to his books now. 



E 



