RHIZOME OF PTERIS. 175 



illustrate it. For considerations of space a small stele has had to 

 be selected for representation ; still, all the elements entering into 

 its composition can be sufficiently well represented in the figure. 

 The first things to attract attention are the great scalar if orm 

 vessels (sc) marked with elongated- bordered pits. For the most 

 part these are in contact with one another, and are surrounded as 

 a ,whole by starch-containing wood-parenchyma (lp). At one 

 spot on the small stele figured, or at two or many spots in larger 

 steles, lie a few scalariformly or spirally-thickened, and partially- 

 disorganised protoxylem elements. Vessels and wood-paren- 

 chyma together form the xylem of the stele. Well nigh sur- 

 rounding this we see the wide openings of the sieve-tubes (r), 

 and to these follow externally the cells of the bast-parenchyma, 

 rich in protein contents. The periphery of the bast shows an 

 interrupted layer of still narrower swollen protophloem elements 

 (pr). All these tissues are surrounded by a simple layer of starch- 

 containing cells (P2)), the starch sheath, which is surrounded by 

 the thin-walled but starch-free and corky endodermis (e), which, 

 in the comparatively young state we are studying, shows the 

 dark shadings on the radial walls. The cells of the starch sheath 

 and of the endodermis coincide with one another, and have a 

 common origin. They both arise through the tangential division 

 of the innermost layer of the general ground-tissue, the so-called 

 phloeoterma. The phloeotermatic starch sheath here replaces the 

 pericycle. At the two edges of the xylem strand the sieve-tubes 

 are often wanting, so that wood-parenchyma and bast-paren- 

 chyma (or possibly even the protophloem or the starch sheath) are 

 in direct contact. Not infrequently the section will have skirted 

 the scalariformly-perforated partition wall of a vessel, which may 

 then have the appearance shown on the figure at (sc*). The 

 walls of the endodermic cells are very commonly torn in cutting, 

 so that the stele is separated from the surrounded ground-tissue. 

 The cells of the ground-tissue bordering on the endodermis are 

 here and there strongly thickened, and then coloured yellow- 

 brown. 



The cross-section through the rhizome shows, under the deep- 

 brown epidermis, a brown and cutinised parenchymatous tissue, 

 the so-called " cortical sclerenchyma," which farther towards the 

 interior is colourless and full of starch. This starch-containing 

 ground-tissue is traversed by the steles, and by reddish-brown 

 sclerenchyma fibres. These latter form bands between, and run- 



