124 



CELLULAR TISSUE. 



^rd^ms^c. 



p. crispus, densus, gramineus, no strong thickening occurs), rhizomes of Cyperace^, 

 e. g. Carex hirta, exceptionally also in roots of Dicotyledons (Primula Auricula). 

 Comp. Fig. 51. In many rhizomes of Monocotyledons, e.g. Carices, several thick- 

 walled sclerotic layers occur in the region occupied in allied plants by the endo-, 

 dermis, when fully developed: it remains to be investigated how far these are 



endodermis. 



The thickenmg masses are 



as a rule more or less sclerotic — 

 lignified, or suberised — only in Pr. 

 Auricula do they consist of cartila- 

 ginous, gelatinous cellulose. In 

 relatively few cases they extend in 

 equal thickness round the whole 

 cell ' (root of Pr. Auricula, of many 

 epiphytic Orchids, stem of Pota- 

 raogeton pusillus) ; usually they 

 are more strongly developed on 

 the inner side, than on the outer; 

 roots of species of Carex, Cy- 

 perus, Scirpus, Phragmites com- 

 munis, Triticum repens, Asparagus, 

 species of Smilax (the so-called 

 core-sheath (Kernscheide) of Sar- 

 saparilla roots), Dracaenas, Palms^, 

 and in the above-named rhizomes of 

 Cyperacese, the stems of Potamoge- 

 ton pectinatus, lucens, natans, prae- 

 longus": comp. below, Chap. VIII. 

 The thickening masses are stratified and pitted ; only in the investigated Dracsenese 

 they are not pitted (Caspary). The undulation is not present on the thickened walls, 

 but it again appears on the original radial walls, if they can be isolated by destruc- 

 tion of the superposed thickening masses, e. g. by sulphuric acid. Usually the 

 thickening and sclerosis extend to all the cells almost equally, but thin-walled cells 

 often occur between the others. They are found quite solitary, e. g. often in the 

 root of Auricula (Fig. 51); or numerous, but alternating not very regularly with 

 the thick-walled cells, in the root of Strelitzia ovata. But in the vascular-bundlcr 

 sheath of the aerial roots of epiphytic Orchids 1-2 longitudinal series of cells remain 

 before each vascular group with an unthickened membrane, which turns blue with 

 iodine and sulphuric acid : in their longitudinal course they are here and there inter- 

 rupted by thickened cells *. 



The elements of the endodermis are, in all exactly investigated cases, cells in the 

 fullest sense of the word, with a protoplasmic body ; in Equisetum, according to 



''"^^Q^nPA^ 



Fig. 51. — Primula auricula (225) ; transverse section tlirough the heptarch 

 vascular bundle of an adventitious root and its surroundings. P pericam- 

 bium ; £■ the outer primordial vessels of the vascular rays, which alternate 

 with the seven phloem-groups, and are separated from these by thin- 

 walled parenchyma ; u endodermis ; outside this js rather thick-walled 

 cortical parenchyma, with intercellular spaces tetrangular in transverse 

 section. 



^ Caspary, I.e. p. io8.— Schleiden, Archiv d. Pharmac 1847.— Berg, Atlas d. Pharm. Waaren- 

 kunde, Taf. Ill, IV.— Mohl, Palm, structura.— Karsten, Vegetationsorgane der Palmen, Taf. III. 

 fig. 2. 



^ Caspary, Pringsheim's Jahrb. I. p. 443. 



2 Leitgeb, Wiener Acad. Denkschr. Bd. 24, p. 207. 



