76 



THE OPHIOGLOSSALES 



As in Botrychium and Ophioglossum, the tissue derived immediately from the 

 activity of the apical meristem, after the central pith is developed in the stele, 

 contributes only to this central region or pith, which is really not part of the stele 

 proper. On the dorsal side of the stele the whole of the procambial strand can 

 easily be followed into the leaf, and when this is followed downward it is seen to 

 run obliquely through the youngest internode, at the base of which it joins the next 

 leaf. The latter already has its lamina developed and strongly bent over, but is 

 still inclosed in the stipular sheath belonging to the next older leaf. 



These older leaves have only a single leaf trace, but it divides into two strands 

 above the level of the stipular sheath. A median section of the thick central stele in 



Fig. 51. 



Seven transverse sections from a young sporophyte of Helminlhostachys. X35. /, petiole of leaf- 

 b, terminal bud inclosed by stipular sheath, sh. In G, x is pit between leaf base and internode. 

 H, section of a young leaf, showing the temate lamina. 



the upper region shows conspicuous protoxylem elements made up of much elongated 

 tracheids, whose thickenings are between annular and spiral in form, but very 

 different from the coarsely reticulate and the conspicuously pitted tracheids of the 

 metaxylem developed in the older parts of the stele. In all cases where truly median 

 sections were seen the protoxylem elements occupied the innermost region of the 

 xylem and no metaxylem was seen within these, so that the bundle (at first, at any 

 rate) is endarch, as in the other Ophioglossaceae. It is impossible to see in this sec- 

 tion that metaxylem was developed inside of the protoxylem, as Farmer found to be 

 the case in the older sporophytes. 



