i 7 8 



PART II. VEGETABLE HISTOLOGY. 



nate with masses of sieve tissue ; these alternating masses are 

 not in contact, but separated from each other by thin plates of 

 parenchyma ; and in the centre of the bundle is an area usually 

 consisting of parenchyma, and then constituting a kind of false 

 pith, but sometimes it is filled with xylem tissues to the centre, 

 as in the root of Tradescantia Virginica. 



Kig. 439. 



Fig. 439. — Radial bundle from root of Botrycriinm Virginicum. The bundle is triarch 

 or three-rayed, e is the endodermis; p, the pericambium; />k, a phloem mass; and x, a 

 strongly lignitied xylem ray. 



Imperfect or rudimentary fibro-vascular bundles are of com- 

 mon occurrence. In the ramifications of leaf-veins, for example, 

 the elements of the bundle disappear one by one, until, in the 

 finer branches, but a single element, say a spiral vessel or tra- 

 cheid, may be left, and in many herbaceous plants, particularly 

 aquatics, the bundles are greatly depauperated, so that even the 

 ducts are often wanting. 



The Fundamental System. This is the system of tissues 

 through which the fibro-vascular bundles are distributed. It 

 includes all the tissues of the plant except those which are 

 included in the fibro-vascular and epidermal systems. 



In the lower forms of plant life it usually forms a very large 

 portion of the plant structure, and this is true, also, of the herb- 



