BERNARD AND A. L. DE JUSSIEU 357 



characters will only be available for subordinate 

 divisions.^ 



Augustin Pyrame de CandoUe* subsequently drew 

 the important distinction between ancestral (" morpho- 

 logical") and adaptive ("physiological") characters, 

 though it would be too much to expect that he should 

 have applied his own distinction with perfect con- 

 sistency.^ Like all botanists before 1859, he was still 

 inclined to believe that primary divisions must rest 

 upon characters of great physiological importance, an 

 assumption which, plausible as it is, further experience 

 has much impaired. We now believe that no line can 

 be drawn between the two sets of characters ; those 

 which are now ancestral were once adaptive, a sufficient 

 reason for dropping De CandoUe's terms, "morpho- 

 logical" and "physiological," which imply a dijSference 

 in kind. 



The thirteenth chapter of Darwin's Origin of Species 

 has enlarged and rectified the teaching of both A. L. de 

 Jussieu and Pyrame de CandoUe by demonstrating : — 

 That valuable characters cannot be indicated beforehand 

 by any rules ; that the physiological importance of a 

 structure is no measure of its systematic value, which 

 depends entirely upon the probability of its unbroken 

 transmission from a remote ancestor ; that embryonic 

 characters are not always distinctive of large groups ; 

 that characters drawn from the heart, which A. L. de 

 Jussieu believed to be of the first importance in the 

 classification of vertebrates, worms and insects, are of 

 uncertain, sometimes of very little, value in those 

 groups ; that some external characters (the trimerous 

 flowers and parallel venation of monocotyledons, the 



^Exposition, p. 183. * Thiorie Mimentaire de la botanique, 2nd ed., 1819. 

 'Sachs' History of Botany, Eng. trans., pp. 128, 135. 



