442 MOSSES AND FERNS chap. 



these are dense, and stain deeply, indicating the presence of 

 mucilaginous matter, and probably tannin, their appearance and 

 behaviour being very much like the tannin cells of Angiopteris 

 or Marattia. 



In the older parts of the section the nodal cells remain 

 short, while the internodal cells elongate very much and sepa- 

 rate the nodes with their attached foliar sheaths. With this 

 growth is associated the formation of the characteristic lacunae. 

 In all the large species the growth of the medullary cells very 

 soon ceases to keep up with the expansion of the stem, and 

 they are torn apart and almost completely disappear, leaving a 

 great central cavity in each internode separated from the 

 neighbouring ones by a thin diaphragm, — all that is left of the 

 medulla in the fully-developed stem. The leaves of successive 

 sheaths alternate, and a study of the course of the vascular 

 bundles shows that at each node the alternating bundles of 

 successive internodes are connected by short branches. Corre- 

 sponding to the vascular bundles are ridges upon the surface of 

 the internodes and foliar sheaths, due to greater growth at these 

 points, as a result of which a regular series of cortical lacunae 

 (vallecular canals) is formed, alternating with them (Fig. 227, C), 

 and lying just outside of the cortical zone containing the 

 vascular bundles. In some of the small species of Eguzsetmn, 

 as in the primary shoot, the central lacuna is absent. 



A cross-section of the fully-developed stem of E. telmateia 

 (Fig. 227, C) shows this very regular arrangement of the 

 vascular bundles and lacunae. In addition to the large cortical 

 ones, each vascular bundle has, on the inner side, a large air- 

 space, which like the other is formed by the tearing apart of 

 the tissues of the bundle. In this way the primary tracheids 

 are torn apart and often destroyed, so that all that remains of 

 them are the isolated thickened rings adhering to the sides of 

 the canal. The bundle is strictly collateral in structure, and 

 very much resembles that of many grasses and other simple 

 Monocotyledons. The phloem is composed of sieve -tubes, 

 which, according to Russow,^ have only horizontal sieve-plates, 

 and no lateral ones as in the Ferns. These are mingled with 

 cambiform cells. In the species in question there is in addition 

 a zone of bast fibres, at the outer limit of the phloem. 



Surrounding the whole circle of bundles in E. telmateia, 



^ Russow (i). 



