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XV. — On the Species and Genera of Plants, considered with Re- 

 ference to their practical Application to Systematic Botany. 

 By George Bentham. (Extracted from a Paper read before the Lin- 

 nean Society of London, JNov. 15, 1858.)* 



I say Species and Genera, rather than Genera and Species ; for the whole 

 system of classification depends, in the first instance, on a right under- 

 standing of what is meant by species. 



The Species, in the ordinary traditional acceptation of the word, de- 

 signates the whole of the individuals supposed to be descended from one 

 original plant, or pair of plants. But this definition is practically use- 

 less — for we have no means of ascertaining the hereditary history of in- 

 dividual plants — and is considered theoretically incorrect by those who 

 deny the original creation of a certain number of individuals, or pairs of 

 individuals, forming each a parent stock, from which as many con- 

 stantly distinct races have descended. It has, therefore, been proposed 

 entirely to reject descent as an element in the definition of species, and 

 to consider as such any set of individuals which present, either in their 

 external form, or in their internal structure, or in their biological phe- 

 nomena, any common character, or combination of characters, distin- 

 guishing them from all others. But in nature there are no two indi- 

 viduals exactly alike in every respect. In all collections of individuals, 

 even when the immediate offspring of one parent, peculiarities will be 

 found common to some, and not to all. The species or collection of in- 

 dividuals thus defined, becomes, therefore, as arbitrary as the genus or 

 collection of species, and reduces the rules of classification in the one 

 case, as in the other, to little more than rules of convenience. 



Believing, however, as I do, that there exist in nature a certain num- 

 ber of groups of individuals, the limits to whose powers of variation are, 

 under present circumstances, fixed and permanent, I have been in the 

 habit of practically defining the species as the whole of the individual 

 plants which resemble each other sufficiently to make us conclude that they 

 are all, or may have been all, descended from a common parent. Their va- 

 riations would be such only as we observe among individuals, which we 



* The great length to which this paper, read at three different meetings of the Society, 

 extended, prevented its immediate publication, and the subsequent appearance of Mr. 

 Darwin's work rendered obsolete the short allusions I had made to the theories advanced 

 on the origin of species. The present extract, however, is purely practical, relating to 

 species as they now exist, and have existed within historical periods, quite independently 

 of their theoretical origin. 



