MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS. 367 



caution. After being thus treated, the tissue should be boiled in alcohol, 

 and then in water; and it will then be found very easy to tear apart the 

 individual cells, ducts, etc., of which it may be composed. These may 

 be preserved by mounting in weak spirit. 



365. Stem and Root. It is in the stems and roots that we find the 

 greatest variety of tissues in combination, and the most regular plans of 

 structure; and sections of these viewed under a low magnifying power 

 are objects of peculiar beauty, independently of the scientific information 

 which they afford. The Axis (under which term is included the stem 

 with its branches, and the roots with its ramifications) always has for the 

 basis of its structure a dense cellular parenchyma; though this, in the 

 advanced stage of development, may constitute but a small portion of it. 

 In the midst of the parenchyma we generally find ' fibro-vascular ' 

 bundles, consisting of woody fibre, with ducts of various kinds, and 

 (very commonly) spiral vessels. It is in the mode of arrangement of 

 these bundles, that the fundamental difference exists between the stems 



. 251. 



Transverse Section of Stem of young Palm. Portion of Transverse Section of Stem of 



Wanghie Cane. 



which are commonly designated as endogenous (growing from within), 

 and those which are more correctly termed exogenous (growing on the 

 outside): for in the former the bundles are dispersed throughout 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 inclosed in an envelope of the 

 same substance that forms the bark. These two plans of Axis-formation 

 respectively characteristic of those two great groups into which Phanero- 

 gams are subdivided namely, the Monocotyledons and the Dicotyledons 

 will now be more particularly described. 



366. When a transverse section (Fig. 250) ofamonocotyledonousStem. 

 is examined microscopically, it is found to exhibit a 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 



