THE FIBRO-VASUULAR SYSTEM. 



119 



and phloem is so marked that they are said to be composed 

 of corresponding tissues, (1) Vascular, (2) Fibrous, and (3) 

 Parenchymatous. * The vascular tissues are, on the one 

 hand, the tracheary tissue found only in the xylem, and on 

 the other, the sieve tissue of the phloem. The fibrous tissue 

 of the xylem is the variety with the shorter and harden 



Fig. 108. Cross-section of the flbro-vascular bundle of an old adventitious root of 

 Ranunculus repens. gr, a, g, the outer margins of the radial plates of tracheary tissue ; 

 r, a large central pitted vessel ; x , septum in pitted vessel, with its central portion 

 absorbed ; p, pericambium ; u, bundle sheath ; between the four projecting parts of 

 the tracheary portion of the bundle, and just within the pericambium, lies the sieve 

 tissue. X 145. After De Bary. 



fibres, known as wood fibres ; that of the phloem is com- 

 posed of the longer and tougher bast fibres. The paren- 

 chyma of the two portions is much alike. 



* Attention should be called here to the fact that in a good many 

 orders of Phanerogams the laticiferous vessels are constituent parts of 

 the fibro-vascular bundles. Thus in Cichoriaceae, Campanulaceae, 

 Papaveraceae, Asclepiadaceae, Apocynaceae, and Acerinese they occur in 

 the phloem; in Papayaceae and Aroideae they occur in the xylem. 



