XII 



EQUISETINEsE 



463 



greater part remains but little changed. By this time, in 

 E. telmateia, numbers of cells with peculiar contents are noticed 

 scattered through the pith and cortex (Fig. 269). The con- 

 tents of 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 Angiop- 

 teris or Marat tia. 



In the older parts of the section the nodal cells remain short, 

 while the internodal cells elongate very much and separate the 

 nodes with their attached foliar sheaths. With this growth is 

 associated the formation of the characteristic lacunae. In all 



' ' 



FIG. 269. Longitudinal section of the young stem, showing the junction of the foliar 

 and internodal bundles; tr, the primary tracheids; x, x, tannin-bearing cells. 



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 cen- 

 tral 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 alter- 

 nate, and a study of the course of the vascular bundles shows 

 that at each node the alternating bundles of successive inter- 

 nodes are connected by short branches. Corresponding to the 



