90 Mr. R. B. Hinds on Geographic Botany. 



are prolific; the temperate regions liave also their dense and 

 gloomy forests ; in fact it is beyond all human possibility to form 

 any numerical estimate of the amount of the vegetable kingdom ; 

 it would be like counting the sands of the Great Sahara. Let the 

 imagination picture all it can of multitade^ space, and prolific 

 increase, and some conception may be conveyed to the mind. 



Every botanical region of the globe possesses a flora having 

 features which proclaim relations with other regions ; these 

 vary according to the nature of the relationship and the circum- 

 stances under which the respective floras exist. The value of the 

 points of connexion fluctuates as the comparisons are drawn from 

 groups of plants united by general characters, or from others 

 less common and more intimately connected with their existence. 

 The modes of relation are three in number, corresponding in a 

 general manner with the three assemblages of vegetable forms 

 known as families, genera, and species. By the families are esta- 

 bUshed the most distant and general resemblances, constituting 

 analogy ; by the genera a closer approximation, or affinity ; and by 

 the species the most perfect accordance of characters, or identity. 



Generally these modes of resemblance coincide with the paral- 

 lel groups ; but there are instances of analogy and afiinity, which 

 must be admitted as such, and yet are not so closely limited. 

 As an instance of this kind, as regards analogy, may be men- 

 tioned the existence of Ficoidece chiefly in South Africa, and of 

 CactecB almost entirely in the two Americas. The analogical re- 

 semblance arises from the great succulence met with in these 

 two families, together with a certain correspondence in their 

 organic structure. A further illustration occurs in the alpine 

 flora of the Canaries and Mount Etna ; in the former Semper- 

 vivum has numerous species, and not one is indigenous to the 

 latter, where Sedum is nearly equally abundant. Whilst then it 

 is admitted that there is some difficulty in fixing the precise 

 limitation of these terms, they may be considered, as a rule, to 

 display the coincidence expressed above. 



Whenever an analogy exists, it by no means follows that there 

 should be a further connexion by affinity or identity, for the na- 

 ture of the analogical resemblance does not require this. On the 

 other hand, when there is an affinity between two regions, it 

 presupposes also an analogy ; and when the relation is so intimate 

 as to estabhsh an identity, there is necessarily both an analogy 

 and an affinity. 



The sources of analogy being derived from natural families, 

 and the latter as we have seen usually widely diff'used, they are 

 abundant in all vegetable regions, founded on latitude, which 

 approach each other. In the tropical regions throughout, there 

 is a great similarity in the families, those existing in one or more 

 being often common to the others. In the subtropic and other 



