SECT. I 



MORPHOLOGY 



10iJ 



Fig. 124. — Transverse section of an internode of 

 the stem of Zm J\Iais. pr, Primary cortex ; 

 pc, pericycle ; cv, vascular bundles ; gc, funda- 

 mental tissue of the central cylinder, (x 2.) 



soon becomes apparent. The outer tissues are best adapted for pro- 

 tection, the inner for conduction and storage. The cells of the inner 

 tissues accordingly become elon- 

 gated for the purpose of conduc- 

 tion. The outer tissues in plants, 

 which must provide independently 

 for their own nourishment, con- 

 tain chromatophores fitted for 

 assimilation, and are correspond- 

 ingly coloured, while the inner 

 tissues remain colourless. The 

 outer portion of the fundamental 

 tissue thus differentiated is called 

 the cortex, the inner the MEDULLA 

 or pith. An epidermis, distin- 

 guishable from the cortex, is found 

 in some of the Mosses, but a sharp 

 distinction between these tissues 

 is first found in the more highly 

 organised plants. 



In the Stem of a Phanero- 

 gamic plant there is an outer skin or epidermis (Fig. 125, e) on 

 the external surface; then follows the primary cortex (Figs. 124, 



125, pr), and internal to this 

 the so-called central cylin- 

 der, for which Van Tieghem 

 ■ has proposed the name stele 

 (column). The innermost layer 

 of the primary cortex, which 

 may be designated by the term 

 PHLOEOTERMA, is for the most 

 part not distinctly differenti- 

 ated, but can be recognised in 

 the aerial stems of land plants 

 as a starch-sheath ; while in 

 the rhizomes of land plants 

 and in the stems of water- 



Fig. 126.— Part of ." transverse section of a young plants it forms the ENDODER- 



stem of AHstoiochm sipho. e, Epidermis ; pr, MIS . Differentiated as a starch- 



primary cortex; st, starch - sheath ; c, central , , ,-*-,. i o k j\ +1, 



cylinder ; pc, pericycle, in this ease with a ring of sneatn (Tig. 1LO, St), tUe 



sclerenchyma fibres ; cr' , phloem, and ra", xylem phloeoterma is rendered COn- 



portions of the vascular bundle; cb, cambium sp i cuous by the quantity of 



ring; m, medulla; ms, primary medullary ray. r . J . . . . ,. 



/ x4S j starch contained m its cells; 



when developed as an endo- 

 dermis, portions of the lateral walls of its cells become suberised. 

 In a cross-section these suberised portions of the cell walls of the 



