250 THE ANATOMY OF STEMS. 



The investigation of which is yet only in its com- 

 mencement, and much remains to be done before 

 their real properties are well understood. 



CHAPTER III. 



THE ANATOMY OF STEMS. 



The advocates for the natural method of classifying 

 plants, distinguish them into two grand divisions, name- 

 ly, the Monocotyledons and Dicotyledones ; each of 

 which displays a distinct internal system of organiza- 

 tion, as well as the better known and more obvious 

 distinctions of physical and botanical relations. In 

 the plants of the first class (JSionocotyledones) the stem 

 simply consists of bundles of woody fibres and vessels, 

 interspersed through a cellular substance, and decreas- 

 ing in solidity from the circumference to the centre ; 

 but in those of the second, it is composed of concentric 

 and divergent woody layers, decreasing in solidity in 

 the opposite ratio, or from the centre to the circum- 

 ference, and containing a pith in a central canal. 



Another anatomical division, however, is requisite 

 for the classification of the Acotyledonous and Aga- 

 mous plants, such as the Ferns, Mosses, Alga?, and 

 Fungi ; whose sterns display internally, an apparently 

 homogenous mass, and when examined by the unas- 

 sisted eye, seem to consist simply of an epidermis 

 enclosing a parenchyma, composed either of cellular 

 substance, of different degrees of succulency, spongi- 

 n; ss, dryness, and density ; or of interwoven fibres, 

 forming a leathery, or felt-like texture, 01 me not a 

 little resembling that of washed animal muscle, after 

 maceration in spirits- When examined, however, 

 by the aid of a good microscope, these different ap- 



