M. Cli. Naudiii on Hyhridity in Plants. 235 



and not lose sight of the fact that all our ideas arise from 

 the contrast of things. 



The man blind from birth has no idea of darkness, because 

 being deprived of the sensation of light he does not perceive 

 the difference between the two ; even one possessed of sight 

 would have no idea of the light which surrounds him if the 

 whole world was luminous and that to the same degree. 

 The notion of species does not escape the common law ; 

 it is more complex, and is formed from more elements, as 

 we shall attempt to elucidate. 



If there existed in nature but 07ie vegetable form, wheat 

 for instance, always and everywhere alike, without any 

 variation in the innumerable individuals which represent it, 

 we might arrive at the idea of an individual and vegetable, 

 but not species ; wheat and vegetable would be confounded 

 in one's mind as one and the same thing. 



Let us suppose also that nature had created an inde- 

 terminate number of different organisms, and each of them 

 represented on the earth by only a single individual, inca- 

 pable of multiplying itself, but indestructible and imperish- 

 able ; even here we could not arrive at the conception of a 

 species, for each type of organisation would be isolated, and 

 have no resembling individual. 



To have a species it is necessary, therefore, 1st, To have a 

 plurality of similar individuals, that is to say, a group, a col- 

 lection ; 2(i, That this group or collection of individuals con- 

 trast in some degree with other groups of individuals likewise 

 resembling each other, and yet able to approach one an- 

 other in some common points which render them comparable. 



It follows that the idea of species is connected with that 

 of kind or genus (I mean genus taken in a philosophical 

 sense) ; that the one fact always supposes the other ; that, 

 in a word, they are inseparable and unable to exist apart. 

 And as, in the organic world, individuals have a transitory 

 existence, reproducing themselves by generation, it is neces- 

 sary, ^dly, In order that species may have consistence and 

 duration — that the resemblance of individuals forming a spe- 

 cific collection shall continue in successive series of generations. 



Thus a plurality of similar individuals forming a group, 

 and the contrast of groups among themselves by certain 



