STEM OF ZEA MAIS. 109 



from the inner towards the outer edge of the bundle. We then 

 see that to the broad cells of the ground-tissue, in outline well- 

 nigh square, succeed narrower ground-tissue cells, and after these 

 follow the narrow elements of the vascular bundle-sheath (vg). 

 These last elements, deeply stained with corallin, show marked 

 elongation, join one another with more or less inclined end-walls, 

 and are provided with small, cleft-like, obliquely ascending pits. 

 In the interior of each is to be found a lining layer of protoplasm 

 of very reduced dimensions, and a small nucleus. From the 

 nature of their pits we shall recognise these as sclerenchyma 

 fibres, although they do not all possess the typical form of fibres, 

 to wit, sharply tapering ends. To the cells of the sheath suc- 

 ceeds the intercellular passage, and we can determine that, 

 unless the section is cut obliquely, it follows without interruption 

 the whole length of the bundle. It is surrounded by thin-walled 

 wood parenchyma, the cells of which are far shorter than the 

 elements of the sheath, have more cell-contents, and have hori- 

 zontal walls. Into the intercellular passage project usually 

 isolated rings ; they are attached to the outer side of the inter- 

 cellular passage, i.e., to the side nearest the periphery of the 

 stem. They arise from an annular vessel (vascular trachei'de) 

 torn during the elongation of the internode. Other smaller 

 isolated rings may also often be seen clinging to this or the other 

 side of the intercellular passage (a). Collectively they represent 

 the remnants of the protoxylem. Impinging outwardly on the 

 larger rings are one or several broader or narrower spirally or 

 reticulately thickened vessels (vascular tracheides). In the case 

 represented in Fig. 41, only one such was cut through, and that 

 a somewhat narrow one (sp). Next follow comparatively short 

 wood cells, with pitted or reticulately thickened walls, and be- 

 tween them also thickened trachei'dal elements. Thus we arrive 

 at the bast or phloem portion, recognisable in the corallin pre- 

 paration by some thick rose-red coloured cross-walls, the sieve- 

 plates of the sieve-tubes (v). These sieve-plates are highly 

 refractive ; and stronger magnification shows that they are 

 pierced by fine pores, after the fashion of a sieve, and that on one 

 side, seldom on both, is collected a highly refractive plug of 

 " slime," due, however, to the method adopted in preparing the 

 section. In the periphery of the bast (at cp), where in the cross- 

 section were visible the swollen cell-walls of the protophloem 

 elements, a specially beautiful rose-coloured cross-wall appears. 



