252 



PTERIDOPHYTA. 



[CH. 



significance of these statements will be realised when the 

 structure of the extinct genus Galamites is described and 

 compared with that of Equisetum. 



The small drawing in fig. 55, 3 shows part of the ring of 

 thick nodal wood ; the section cuts through two bundles about 

 their point of bifurcation, the strand x is passing out in a 

 radial direction to a lateral branch, the strand to the right of 

 X and the separate fragment of a strand to the left of x are 

 portions of leaf-trace bundles on their way to the leaf-sheath. 

 Reverting to fig. 54, B, the other structures seen in the section 

 are the leaf-sheaths {I and m), the vallecular canal (/), the 

 epidermis, cortex and pith {k, e and a) of the stem. The 

 epidermis which has been ruptured by the root and branch is 

 indicated at i, i ; the dotted lines traversing the upper part of 

 the pith of the lateral branch mark the position of a nodal 

 diaphragm. 



Fig. 55. 1. Transverse section of a root of Equisetum variegatum Schl., eendo- 

 dermis, or outer layer of the phloeoterma (after Pfitzer; x 160). 2. Trans- 

 verse section of rhizome of E. maximum, slightly enlarged. 3. Transverse 

 section through a node of E. maximum, x, branch of vascular strand (slightly 

 enlarged). 4. Transverse section through a node of E. maximum showing 

 the mass of xylem, px protoxylem ( x 175). (Figs. 3 and 4 after Cormack.) 



Immediately external to each vascular strand, as seen in 

 transverse section, there is a layer of cells containing starch. 



