110 



BOTANY. 



differentiated, being composed of parenchyma and poorly 

 developed sieve tubes (s, Fig. 97). The whole bundle is sur- 

 rounded, as in Pteris aquiUna, by a bundle sheath (u, Fig. 

 97). In the outer part of the mass of scalariform tissue are 

 a few narrow spiral vessels (sp, sp, Fig. 97), but they are 

 not sufficiently numerous to constitute a ring or layer. 

 138. In the root of Adiantum Moritzianum the bundle 



consists of a cen- 

 tral plate of tra- 

 cheary tissue ( pr, 

 Fig. 98), with a 

 mass of sieve 

 tissue on each 

 side of but not 

 quite enveloping 

 it. Next outside 

 of this is a layer 

 of active paren- 

 chyma, the peri- 

 cambium (pc, 

 Fig. 98), and sur- 

 rounding the 

 whole is a poorly 

 developed bundle 

 sheath (u, Fig. 

 98). 



139. In the 

 stem of Equise- 



Fig. 99. Transverse section of a fibre-vascular bundle of , -, , 

 Equisetum palustre. r, t, ringed vessels on the border of a tUTIl pttLUSlTv It 

 large intercellular canal; , sieve tissue; g, ff, groups of . 

 annular and reticulated vessels ; w, the so-called general J ldD J ' 

 bundle sheath, which surrounds all the bundles ; i, i, axial , J-T-.Q -fVvrpo-m no- 

 air canjJs ; x , x , fragments of the ruptured cells. X 145. m " 

 -After De Bary. cases to mark the 



limits of the bundles, which are arranged in a circle about 

 the axis.* On the axial side of each bundle there are at 

 first a few spiral and annular vessels, most of which, 

 along with a considerable amount of parenchyma, are 



* In Equisetum limosum, however, there is a bundle sheath about 

 each bundle, consequently there is in that species no difficulty as to 

 the limits of the bundle. 



