HISTOLOGY OF THE RHIZOME. 



79 



taining protoplasm and having the walls marked by areas per- 

 forated by numerous fine pores (panelled). They join at the 

 ends by oblique panelled partitions (shown in Figs. 40 and 41). 



5. Phloem-parenchyma ordinary parenchymatous cells filled 

 with starch, scattered here and there among the bast-fibres and 

 sieve-tubes. 



6. Tracheids (scalariform) or " ladder-cells ;" occupying most 

 of the central part of the bundle. Their structure calls for some 

 remark. They are empty or air-filled fusiform tubes, whose 

 hard, thick walls are in the young tissue sculptured with great 

 regularity into a series of transverse hollows or pits, which finally 

 become actual holes. Tke walls of the tracheid are therefore 



Jp. b.s bf pp. t. tap. t. w.p. f pp. bfl hs f.f* 







i -.J - 







FIG. 40. Longitudinal section of a fibre-vascular bundle, surrounded by the fundamental 

 parenchyma, b.f, bast-fibres; b.s, bundle-sheath; f.p, fundamental parenchyma; 

 p. p, phloem-parenchyma; p.s, phloem-sheath; s.t, sieve-tubes; f, scalariform tracheids 

 or ladder-cells ; w.p, wood-parenchyma. 



continuous at the angles, but along their plane surfaces become 

 converted into a series of parallel bars, making a grating of singu- 

 lar beauty. The slits between the bars are not rectangular pas- 

 sages through the wall, but are rather like elongated, flattened 

 funnels, opening outwards. The sides of the funnels are called 

 the borders of the pits and pits of this sort are called bordered 

 scalariform pits (cf. Figs. 29 and 40). 



1. Vessels (spiral) ; scattered here and there among the 

 tracheids, and hardly distinguishable from them in cross-section. 

 They are continuous elongated tubes filled with air, and strength- 

 ened by a beautiful close spiral ridge (sometimes two) which runs 

 round the inner face of the wall (Fig. 39). 



