LECT. VII.] ANATOMY OP STEMS. 289 



ticism, and probably none can be devised alto- 

 gether unobjectionable; yet, if by any the examina- 

 tion can be facilitated, the attempt to form one, 

 as nearly perfect as the nature of the subject will 

 admit of, is at least praiseworthy. 



The only arrangements which I shall notice, 

 are those of Desfontaines and Mr. Keith. Des- 

 fontaines' method is founded on the fact, that 

 there are two grand divisions of plants, the Mo- 

 nocotyledonous * and Dicotyledonous -f~ ; each of 

 which displays a distinct and specific mode in the 

 distribution of the parts of the stem. In the in- 

 dividuals belonging to the first, the stem consists 

 of bundles of woody fibres and vessels, inter- 

 spersed throughout a cellular substance, and de- 

 creasing in solidity from the circumference to the 

 centre ; in those of the second it is composed of 

 concentric and divergent woody layers, decreas- 

 ing in solidity in the opposite ratio, or from the 

 centre to the circumference, and containing a 

 pith in a central canal J. But, as Mr. Keith has 

 justly observed, this arrangement does not ex- 

 haust the subject : as, independent of the Poly- 

 cotyledonous plants which may be classed with 

 the Dicotyledonous, there is no account taken of 



* Plants, the seeds of which have one lobe only, 

 f Plants, the seeds of which have two Lobes, 

 t Vide Mem. de V Instil. Nat. tome i. 



VOL. I. U 



