40 FLORA INDICA. 



1. As regards specific centres, we proceed in our investiga- 

 tions on the assumption that all the individuals of a unisexual 

 plant proceeded from one originally created parent, and all of 

 a bisexual from a single pair. To discuss this subject would 

 be out of place here : for a resume of the principal facts op- 

 posed to it, as well as of those which support it, we must re- 

 fer our readers to Sir Charles LyeU's ' Principles of Geology,' 

 and to the Introductory Essay to the Flora of New Zealand. 

 It is sufficient for our present purpose to declare, that after 

 many years' unprejudiced careful consideration of the subject 

 in all its bearings, during which period we have been fettered 

 by no professed opinion to support, and have had no inculcated 

 theory to eradicate, we have been independently led to this 

 conclusion, as being most consonant with our very consider- 

 able experience in the field and herbarium. 



3. In attributing the present dispersion to natural causes, 

 we by no means limit them to existing ones. We have every 

 reason to believe that many living species of plants have sur- 

 vived the destruction of large continents, just as many animals 

 have ; that in short they have outlived recent geological changes, 

 of whatever magnitude, that they have witnessed gradual but 

 complete revolutions in the relative positions of land and sea, 

 and consequently in the climate of the several parts of the 

 globe. Such an antiquity is proved for shells especially, and 

 to a greater or less degree for aU tribes of the animal king- 

 dom ; the amount of evidence depending solely on the adap- 

 tation of their dead parts to preservation in a recognizable 

 condition. Fossil plants are specifically never thus to be iden- 

 tified, and our argument is hence one founded on analogy only, 

 but supported by many facts* in distribution, not less than by 

 the efiects of such operations as we now see in progress. 



* Sir Charlea Lyell was the first to appreciate this most important ele- 

 ment in geographical distribution (Principles of G-eology, chap, xxxiii.) ; and 

 Professor Edward Forbes first brought it to hear upon an existing Fauna and 

 Flora, in his admirable Essay on the ' Distribution of the Plants and Animals of 

 the British Islands' (in the 1st vol. of Mem. G-eolog. Surrey of U.K.). We 



