126 



RHIZOME OF PTERIS. 



[CH. IX 



Both xylem and phloem contain vessels and paren- 

 chyma. 



In both the vessels are built up of elongated cells 

 one overlapping the next. 



The xylem vessels have lignified walls and no proto- 

 plasmic contents. 



The phloem vessels, or sieve-tubes, have cellulose walls 

 and intercommunicating threads of protoplasm piercing 

 the sieve-plates. 



Inside the pericycle is a layer of small cells, the 

 protophloem 1 , and inside this again is a layer of large 



A 



jt scu. 



Fia. 55. 

 LONGITUDINAL SECTION OF THK RHIZOME OP Pteris. 



p, parenchyma. 



e, endodermis. 



p.p, protophloem. 



sc.v, scalariform vessels. 



s, sclerenchyma. 

 p.s, pericycle. 

 s.t, sieve-tubes. 



1 In the rhizome of Pteris the protophloem is sometimes continuous 

 all round the bundle, although the fully developed phloem is discon- 

 tinuous and does not completely surround the xylem. 



