48 



BOTANY. 



lariform tissue are masses of soft tissue (parenchyma) and 

 a few spiral vessels, the latter occurring near the foci of 

 the elliptical cross-section of the bundle (s). Surrounding 

 or partly surrounding the tracheary portion of the bundle 

 is a layer of sieve-tubes (sp), separated from the large sea- 



Fig. 31 .—Part of a transverse section of the flbi'O-vascular bundle of the under- 

 ground stem of the common Brake-fern (Pteris aquilina). s, spiral vessel; g, ff, 

 scalarlform vessels; sp, sieve-tissue; b, fibrous tissue; sg, bundle-sheath. 



lariform vessels by a layer of parenchyma. Outside of the 

 sieve-tissue is a mass of fibrous tissue (b), which is itself 

 bounded externally by another layer of parenchyma. The 

 whole bundle is surrounded by a bundle-sheath. 



89. A noticeable feature in the structure of this bundle 



