THE GROUPS OF TISSUES, OB TISSUE-SYSTEMS. 51 



Soft Cells. The vessels are the tracheary tissue in the 

 xylem and the sieve-tissue in the phloem. The fibrous 

 tissue of the xylem is the variety with the shorter and 

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

 composed of the longer and tougher bast-fibres. The soft 

 tissue (parenchyma) of the two portions is much alike. 



Fig. 33.— Fibro-vascular bundle of root of Sweet Flag (Acorus). pp, 

 plates of tracheary tissue ; g, y, pitted vessels ; ph, sieve-tissue ; s, bundle- 

 sheath. 



87. In the fibro-vascular bundle of the young roots of 

 Sweet Flag there are many radially placed plates of trache- 

 ary tissue (pp, Fig. 33), which alternate with thick masses 

 of sieve-tissue {ph). Between these alternating tissues, and 

 within the circle formed by them, there is a mass of soft 

 tissue. The whole bundle is separated from the large- 

 celled soft tissue of the root by a well-marked bundle- 



