24 FLORA INDICA. 



all this proves nothing ; but when we add the tacit acquies- 

 cence of Robert Brown^ and of all other botanists who have 

 lived amid a tropical vegetation^ and devoted themselves to 

 its study, it will not be considered surprising that we should 

 suspect such evidence as has hitherto been adduced by local 

 observers only, and in very limited areas. 



The subject of hybridization is however well worthy of the 

 attention of the tropical botanist ; and both in his garden and 

 in the field, he should keep his attention always alive to the 

 importance of observing every phenomenon that may bear 

 upon its agency, and should institute operations that will 

 throw light upon the subject. 



B. On Variation of Species. 



Although the researches of naturalists have not hitherto 

 led to the detection of those laws in obedience to which many 

 species of plants vary much in one climate and less in others, 

 or remain constant throughout many climatic conditions, they 

 indicate the operation of certain, general laws, whose effects 

 are as follows : — 



1 . Contiguous areas, with different climates, are peopled by 

 different species of plants, and not by the same under differ- 

 ent forms. 2. Similar climates in distant areas are not peopled 

 by the same or even similar species, but generally by different 

 natural orders of plants. 3. Both contiguous and remote areas 

 contain a certain admixture of species common to two or all 

 of them, which retain their iudividuality under every change 

 of climate. 



These are generally admitted facts ; there are however ex- 

 ceptions, upon which are based the arguments for attributing 

 to climatic effects the creation of many species from one vari- 

 able type. Careful observation reveals many such exceptions ; 

 and the tendency which plants display to revert to one typical 



species. The contrary inference, that species are subject to a certain amount of 

 variation, does not seem to have occurred to him. 



