SPECIES BY INFINITESIMAL VARIATtONS. 7 



instead of having one large tooth and four small ones, or to 

 iiave its flowers in (apparent) racemes instead of in true cymes ? 

 The same may be asked with regard to any of the other 

 characters,* so that if any or all of these characters are 

 correlated with advantageous cliaracters, these latter must be 

 purely internal. 



In the second place, Coleus elongatus is much too different 

 a species from the other species of this genus, whether in 

 Ceylon, India, or elsewhere, to have been evolved rapidly 

 by means of continuous variations. The process must have 

 taken a very long time, for the differences are about sufficient 

 to mark a sub-genus. Now , it is hardly to be supposed that the 

 ancestors of the existing plants can have been upon Ritigala 

 long enough for this to have taken place. No other species 

 with a calyx or with an inflorescence like those of C. elongatus 

 occurs in India or Ceylon. 



In the third place, the species is too entirely different from 

 the other species of Coleus, whether we take C. harhatus or one 

 of the others, for evohition by means of continuous variations 

 to have been possible. To take some of the characters, es- 

 pecially those that are most prominent, how is the one type of 

 inflorescence going to develop into the other by any possible 

 continuous variation ? The mind cannot conceive of such a 

 process, unless it be by discontinuous variation. Still more, 

 how is a calyx with one big tooth on top and four small ones 

 below going to develop into one with five equal teeth ? The 

 study of infinitesimal variation shows that the maximum 

 change to be expected in one generation would be a mere 

 fraction of the width of a tooth, and how is this to prove of 

 sufficient advantage or disadvantage to be of any material 

 import in the struggle for existence ? The question is equally 

 hard if we suppose a common ancestor, for what kind of calyx 

 or inflorescence will be intermediate ? 



* Some of these would even seem to be disadvantageous, e.g., the 

 thin leaves in a dry exposed situation, and the small flowers of pale 

 colour. 



