Philosophical Character of Decandolle. 207 



of an higher order have put forth, and that in their conversa- 

 tion, rather than in their writings, being still amongst the 

 number of those opinions which Bacon named floating, be- 

 cause, having never been methodically expounded, they never 

 could be seriously discussed." 



Now, the principles on which a natm-al classification pro- 

 ceeds, are composed essentially of three parts. \st, An estima- 

 tion of the relative importance which we ought to assign to the 

 several organs compared one with the other. 2d, A know- 

 ledge of the circumstances which may lead the observer astray 

 relative to the true nature of these organs ; and, Zd, An esti- 

 mation of the importance which ought to be attributed to each 

 of the points of vietv under which the same organ admits of 

 being regarded. 



With respect to the 1st and 3d of these, — namely, the 

 importance of the several organs considered relatively, and 

 the importance of the several points of view in which the 

 same organ may be regarded, — Decandolle has done nothing 

 more, than to reduce to a system the rules upon which Jussieu 

 and other preceding botanists had proceeded in their natural 

 arrangements of plants, and to explain the principles upon 

 which their rules were founded, or by which they admit of 

 being justified. 



But, with respect to the 2d part, namely, the appreciation 

 of the circumstances which may lead the observer asti'ay as to 

 the true nature of the organs themselves, he has the merit of 

 having unfolded a theory, at once ingenious and philosophical, 

 of the highest practical utility with reference to the details of 

 botany, and calculated to simplify, as well as to enlarge, our 

 ideas with respect to the organization of vegetables. 



In my Inaugural Lecture on Botany I have already presented 

 a sketch of this one of Decandolle's treatises, which, though 

 concise, may perhaps serve as a sufficient account of it for the 

 present occasion. 



" The causes which bring about a deviation from the 

 normal structure of a particular part, and thus lead a botanist 

 to take a mistaken view of its nature, or at least of its struc- 

 ture, may be reduced to three : 1*/, The abortion of some one 

 or more of those organs, which, in the regular course of things, 



