THE FIBRO-VASOULAR SYSTEiT. 



m 



destroyed shortly after their formation, thus forming a 

 wide canal (Fig. 99 ; t, spiral, and r, annular yessela 

 on the border of the canal). Immediately in front of or 

 outside of the canal is a considerable mass of sieve tissue, 

 made up of true sieve tubes and the nearly allied cambiform 

 or latticed cells 

 (s. Fig. 99). 

 Eight and left of 

 the sieve tissue 

 lie a few annular 

 and reticulated 

 vessels {g, g, Fig. 

 99). Exterior to 

 all the bundles 

 (in this species) 

 is a cellular lay- 

 er, which ha3 re- 

 ceived the name 

 of bundle sheath, 

 but which, prob- 

 ably, has no rela- 

 tion to the lay- 

 er so named that 

 surrounds each 

 fibro - vascular 

 bundle of some 

 plants. 



140. — The 



StrncHire of the mg.iWi.— CmsB-seoaoiiot Vaestem of SelagineUainmgvi^ 



■L ji ■ o 7 • /o'i«, showing three bundlee; in each bundle the inner 



DUnuie in oelCigi- thicker waited tissue is composed of FCiilarifdrm vessels, 



*i/j77/y ^mron^i';fnlift "''■*' * '^'^ narrow spiral vessels on each extreme margin: 



ftVHU, ifiun^iiijviiUi surrounding the scalar'form tissue is the thinner walled 



>>oora a nnnoirlpi. sieve tissue, and around this again is a layer of cells which 



oears a. consmei - ^^^ ^e called the bundle sheath ; I, I, intercellular space* 



able resemblance s>ifro™ding the bundles, x ISO.— After Sachs. 



to that of Pteris aqttilina. There is in each bundle a. 

 central plate of tracheary tissue, consisting of a few narrow 

 spiral vessels in its two edges and a remaining mass of scala- 

 riform vessels (Fig. 100). The tracheary poirtion is sur- 

 rounded by a tissue of elongated, thin-walled tissue which 

 is, at least in part, a sieve tissue. In this and allied species 



