The Rev. P. Keith on the Internal Structure of Plants. 117 



destitute of the aforesaid layers, all dicotyledonous plants are 

 not furnished with them. The caudex of Water-Hemlock 

 (Cicnta virosa) exhibits no traces of layers, whether concen- 

 tric or divergent, though belonging to the dicotyledonous 

 class; and the bulb of the common Onion (Allium Cepa) is 

 furnished with concentric layers, at least, though belonging to 

 the monocotyledonous class. In short, there are great diffi- 

 culties resulting from the adoption of this principle. Where 

 are we to place the Filices; where the Orchidece'i And from 

 what are we to take our distinctions? From the seed, or from 

 the plant? To these questions no satisfactory answer can be 

 given ; and hence it is evident, that if any general division 

 arising from internal structure is to be adopted, it must not be 

 instituted upon the ground of the number of the cotyledons. 



As all our classifications of the works of nature are but 

 arbitrary groupings, and are but seldom commensurate with 

 the arrangements of the Divine mind, we can scarcely expect 

 to find a classification that shall be unexceptionable. The fol- 

 lowing divisions are advanced, not with any pretension to 

 peculiar accuracy or excellence, but merely as exhibiting a 

 general view of that scale of vegetable organization by which 

 plants are found to ascend from the lowest and least perfect, 

 to the highest and most perfect forms*. 



I. The caudex a homogeneous and cellular mass, pulpy, 

 powdery, crustaceous, or leather-like, not distinctly divisible 

 into trunk and root, not generally furnished with the several 

 appendages of branch, leaf, and conspicuous flower or fruit; 

 but resolvable merely into an epidermis and an inclosed 

 pulp, or parenchyma. 



II. The caudex a symmetrical .assemblage of heterogeneous 

 organs, vascular as well as cellular, divisible into trunk and 

 root, furnished for the most part with the several appendages 

 of branch, leaf, and conspicuous flower, or fruit; and re- 

 solvable into rind, pulp, and interspersed longitudinal fibre ; 

 the cellular structure predominating. 



III. The caudex a symmetrical assemblage of heteroge- 

 neous organs, vascular as well as cellular, divisible into trunk 

 and root; furnished for the most part with the several ap- 

 pendages of branch, leaf, and conspicuous flower and fruit ; 

 and resolvable into bark, wood, and pith ; the vascular struc- 

 ture predominating. 



The first division comprehends the lowest orders of vege- 

 tables, that is, orders exhibiting the fewest traces of organiza- 

 tion, the caudex being merely a mass of pulp enveloped in a 



* Keith's Phys. Bot., vol. i. p. 286. 



