CLASSIFICATION. 411 



tion. From time to time the notions of naturalists have 

 been greatly widened, especially in the case of Australian 

 animals and plants, by the discovery of unexpected com- 

 binations of organs, and such events must often happen 

 in the future. If indeed the time shall come when all 

 the forms of plants are discovered and accurately de- 

 scribed, the science of Systematic Botany will then be 

 placed in a new and more favourable position, as remarked 

 by Alphonse Decandolle k . 



It ought, I think, to be allowed that though the genea- 

 logical classification of plants or animals is doubtless the 

 most natural and instructive of all, it is not necessarily 

 the best for all purposes. There may be correlations of 

 properties important for medicinal, or other practical 

 purposes, which do not correspond to the correlations of 

 descent. We must regard the bamboo as a tree rather 



O 



than a grass, although it is botanically a grass. For 

 legal purposes we may still with advantage continue to 

 treat as fish, the whale, seal, and other cetacese. We 

 must class plants together according as they are Arctic, 

 or Alpine, or belong to the temperate, sub-tropical or 

 tropical regions. There may be some causes of likeness 

 apart from hereditary relationship, and in a logical and 

 practical point of view we must not attribute exclusive 

 excellence to any one method of classification. 



Classification by Types. 



Perplexed by the difficulties arising in natural history 

 from the discovery of intermediate forms, naturalists have 

 resorted to what they call classification by types. In- 

 stead of forming one distinct class defined by the invari- 

 able possession of certain assigned properties, and rigidly 

 including or excluding objects according as they do or 



k ' Laws of Botauical Nomenclature,' p. 1 6. 



