108 



BOTANY. 



spiral vessels, the latter occurring near the foci of the el- 

 liptical cross-section of the bundle (s, Fig. 96). Surround- 

 ing, or partly surrounding, the tracheary portion of the bun- 

 dle is a layer of sieve tubes (sp, Fig. 96), separated from the 

 large scalariform vessels by a layer of parenchyma. Outside 

 of the sieve tissue is a mass of fibrous tissue (b, Fig. 96), 

 which is itself bounded externally by another layer of paren- 

 chyma. The whole bundle is surrounded by a layer of paren- 



Fig. 97. Transverse section of the flbro-vascular bundle of the rhizome of Polypo- 

 atum vmgare ; sp, sp, narrow spiral vessels in the edge of the mass of scalariform ves- 



3ls; s, region of the sieve tissue filled with parenchyma and poorly developed sieve 

 tissue ; M, bundle sheath, outside of which is parenchyma. X 225. After De Bary. 



chyma differing from the other parenchymatous tissues in 

 not containing starch in its cells ; to this the name of Bun- 

 dle Sheath has been given. 



A noticeable feature in the structure of this fibro-vascular 

 bundle is that the tissues have a concentric arrangement ; 

 the tracheary tissue is encircled by a layer of parenchyma ; 



See, in this connection, an article on " Some recent views as to the com- 

 position of the Fibro-vascular Bundles of Plants," by S. H. Vines, in 

 Qr. Jour. 3fic. Science, 1876, p. 388. 



