14 Transactions of the [Sess. 



IV.— TEE PROBABLE EFFECTS OF A CHANGE OF ELEVA- 

 TION ON THE FLORA OF A COUNTRY. 



By Mk W. TAIT KINNEAE. 

 {Eead 22d Bee. 1881.) 



The object of the present paper is to throw out a few suggestions 

 as to the results which upheaval or depression might produce on 

 the flora of the district where these operations take place. It must 

 not be forgotten, however, that there are other powerful agencies at 

 work. Man has cut down enormous spaces of forest-land, and has 

 drained huge swamps, thus hastening the work of extermination 

 and introducing new plants. Seeds from distant countries are de- 

 posited in ballast-heaps, and often spread far and near, to the injury 

 of native plants. But most effectual of all, we notice that every 

 plant seems tied down more or less strictly to certain conditions of 

 existence, which in most cases it cannot go beyond. When these 

 conditions change slowly or quickly, it is evident that if the same 

 flora is to remain at that locality, it must adapt itself to the altered 

 conditions : if not, then it must be exterminated by those better 

 fitted to exist there. 



The processes of upheaval and depression entail so many changes 

 with them, that it is reasonable to think that in past time they have 

 had some effect in modifying our present flora. Any process that 

 changes the habitats of plants must affect the plants themselves. 

 Upheaval changes the marsh into the plain, and the plain into 

 more or less hilly ground. The effects of upheaval are different 

 in different parts of the world. Thus a few hundred feet added to 

 some of the mountains of this country would develop conditions 

 suitable to the growth of an alpine flora. A depression of two 

 thousand feet without a decrease of temperature would exterminate 

 the greater part of an alpine flora from Britain. If, however, a de- 

 crease of temperature accompanied the process of depression, no 

 material effect would take place, for the alpine flora would descend 

 towards the coast. 



High mountains in the tropics present an epitome of the different 

 zones of vegetation to be found as the traveller moves northwards 

 from the tropics. Agassiz has the following remarks on this point : 

 " The climatic effects of different levels of altitude upon the growth 

 of animals and plants is the same as that of different degrees of 

 latitude ; and the slope of a high mountain in the tropics from base 

 to summit presents in a condensed form an epitome, as it were, 

 of the same kind of gradation in vegetable growth that may be 



