MORPHOLOGY 117 



'of the petioles and flower stems of the Water-Lily these idioblasts are stellate in 

 form. Their walls are strongly thickened, and provided with short protuberances 

 in which small crystals of calcium oxlate are deposited. 



The Distribution of the Primary Tissues ( m ) 



In the body of multicellular plants a distinction between an outer 

 small-celled and firm tissue and an inner large-celled looser tissue 

 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 elongated for the purpose of conduction. 

 The outer tissues in plants, which must provide independently for 

 their own nourishment, contain 

 chromatophores fitted for assimi- 

 lation, and are correspondingly 

 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 Phanerogamic 

 plant there is an outer skin or 

 epidermis (Fig. 128 B, e) on the FK-. I-JT. Tr:msv.-i-s>- sirti.m ui .m mtMiio<ie of 

 external surface ; then follows the th " sti :"' 'f * ^ p , r , ilniiry c ? rte , x : 



' pc, pencycle ; co vascular bundles ; go, fuuda- 



PRIMARY CORTEX (Figs. 127, 128 mental time of the eentnl eyliwter. (x 2.) 

 A, pr), and internal to this the 



so-called CENTRAL CYLINDER, for which VAN TIEGHEM has proposed 

 the name STELE (column) ( 114 ). The innermost layer of the primary 

 cortex, which may be designated by the term PHLOEOTERMA, is for 

 the most part not distinctly differentiated, 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-plants it forms the 

 ENDODERMIS. Differentiated as a starch-sheath (Fig. 128 A, B, 

 xt), the phloeoterma is rendered conspicuous by the quantity of 

 movable starch contained in its cells. A starch -sheath is often 

 present in the young shoots, while it disappears or becomes limited 

 to certain parts of the older shoots ( llr< ). When developed as an 

 endodermis, portions of the lateral walls of its cells become suberised 

 ( uo ). In a cross-section these suberised portions of the cell walls of 



