THB FIBRO-VASOULAE BTSTEM. 



Ill 



destroyed shortly after their formation, thus forming a 

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

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

 outside of the canal is a considei'able mass of sieve tissue, 

 made up of true sieve tubes and the nearly allied cambiform 

 or latticed cells 

 {s, Pig. 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 has i-e- 

 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 



structure of the '^■'i^—CriKB-ieiAvmot^es.UmofSelarilneUainceQm- 



Tmnrllp i^n ,'^plnni sC"'*?' ^'>°^,°-T '•"'ee bundles; in each bundle the inner 



uunuie in OHUlyl- thicker wailed tissue is composed of scalariform vessels 



nplln i-rnvninffiha "''"' * ^j™ "*™w spiral vessels on each extreme margiu • 



rvvuu, inwquijuiia surrounding the scalaritorm tissue is the thinner walled 



bears a consider- "ievej.issue.andaronndthisagainlsalayerof cell-, which 



ued,IS a cuilbiuei m^j. be called the bundle sheath ; I, I, intercc 11 alar spaces 



able resemblance surrounding the bundles. X 150.— After Saehs. 



to that of Pteris aquilina. 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 portion 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 



