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 sca- 
Fia. 31.—Part of a transverse section of the fibro-vascular bundle of the under- 
ground stem of the common Brake-fern (Pteris aquilina). s, spiral vessel; g, 9, . 
scalariform 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 (5), 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 
