290 CONSERVATIVE ORGANS. [LECT. VII. 



those tribes which are altogether destitute of seed- 

 lobes ; the stems of which, in their organization, 

 exhibit neither the woody bundles of the one, nor 

 the layers of the other. Mr. Keith, in order to ob- 

 viate this objection, has arranged stems, in re- 

 ference to their internal structure, into three 

 classes : 1 . The caudex an homogeneous mass ; 

 2. The caudex an heterogeneous mass; and, 3. The 

 mass consisting of bark, wood, and pith*. This 

 arrangement is undoubtedly less exceptionable 

 and more comprehensive than that of Desfon- 

 taines ; but Mr. Keith has erred in arranging, in 

 his second division, the herbaceous stems of dico- 

 tyledonous and polycotyledonous plants ; for, al- 

 though these have no concentrical circles of formed 

 wood, such as characterize the ligneous stems of 

 those tribes, yet the distribution of the ligneous 

 matter and of the pith coincides sufficiently with 

 that of these parts in the real woody stems to 

 allow them to be classed together ; whilst it has 

 little or no affinity with that of the ligneous 

 bundles in the monocotyledonous stems with 

 which they are classed in Mr. Keith's arrangement. 

 A more perfect classification, perhaps, may be 

 formed, by adopting the first division of Mr. Keith's 

 arrangement and adding to it those of Desfon- 

 taines ; as, besides embracing the whole of the 

 subject, it leads us first to the examination of 



* System of physiological Botany, vol. i. p. 287 & seq. 



