THE F1BRO-VA8VULAR 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 harder 



Fig. 108. Cross- 8ection of the flbro-vascular bundle of an old adventitious root of 

 nwm nodus repent. </, a, ff, the outer margins of the radial plates of tracheary tisane ; 

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

 HOsorbed ; p, pericambinm ; 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 tlie fact that in a good many 

 orders of Phanerogams the laticiferous vessels are constituent parts of 

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

 Papaveracese, Asclepiadaceae, Apocynacese, and Acerineae they occur in 

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



