406 



STRUCTURE OF STEM 



-MONOCOTYLEDONS. 



in the mode of arrangement of these bundles, that the fundamental 

 difference exists between the Stems which are commonly designated 

 as Endogenous, and those which are (more appropriately) termed 

 Exogenous ; for in the former the bundles are dispersed through- 

 out the whole diameter of the Axis without any peculiar plan, the 

 intervals between them being filled-up by Cellular Parenchyma ; 

 whilst in the latter they are arranged side by side in such a 

 manner as to form a hollow cylinder of Wood, which includes 

 within it the portion of the Cellular substance known as Pith, 

 whilst it is itself enclosed in an envelope of the same substance 

 that forms the Baric. These two plans of Axis-formation, respec- 

 tively characteristic of those two great groups into which the 

 Phanerogamia are subdivided — namely, the Monocotyledons and 

 the Dicotyledons, — will now be more particularly described. 



299. When a transverse Section (Fig. 212) of a Monocolyledo- 

 nous Stem is examined microscopically, it is found to exhibit a 



Fig. 212. 



Transverse section of Stem of young Palm, 



number of Fibro- Vascular bundles, disposed without any regularity 

 in the midst of the mass of Cellular tissue, which forms (as it were) 

 the matrix or basis of the fabric. Each bundle contains two, 

 three, or more large Ducts, which are at once distinguished by the 

 size of their openings ; and these are surrounded by Woody Fibre 



