72 



THE OPHIOGLOSSALES 



specimen was less developed than that in the specimen that we have just described. 

 This youngest root was cut obliquely, but at its base there could be seen the undif- 

 ferentiated mass of procambium forming its stele, and the apex showed the tetra- 

 hedral apical cell, presenting much the same form as the longitudinal section. The 

 apical portion of the young root was somewhat shrunken away from the surrounding 

 tissue, so that there was a very evident space surrounding it. Whether or not this 

 was the result of artificial shrinkage was not certain. 



Below the terminal bud the third leaf trace proceeds downward into the inter- 

 node below, and the tracheary tissue, which is just beginning to develop in the bud 

 region, increases rapidly in amount and forms a central mass of wood which does 



Fig. 49. — Ten cross-sections from a series of a young sporophyte of Helminthostachys. X25. 



C. Passes through the stem apex, x. The round shaded cells are tannin sacs. 



D. Shows the narrow pit, y, between the leaf base and the axis. 

 G-J. Show only the vascular bundles. 



not appear solid, but is made up of two groups of tracheids, of which the one nearest 

 the second leaf trace has the larger tracheids. At this stage the bundle somewhat 

 resembles the section of a diarch root. Only a little further down the two xylem 

 masses are joined by the development of tracheids in the middle of the bundle, 

 which thus comes to have a solid xylem core. In the section figured there may be 

 seen a single small isolated tracheid on the side turned toward the second leaf trace, 

 which has now approached so close to the central bundle as to touch it (fig. 50, A). 

 The central bundle in the internode at this point is beyond question the leaf trace for 

 the third leaf. There is no diflSculty in tracing its progress upward to where it enters 

 the leaf and there is no sign of any addition to it from tissue lying outside the 

 original leaf trace. The central stele of the upper part of the second internode is 

 throughout nothing more than the basal portion of the leaf trace from the third leaf. 

 At this point it is concentric in structure. Surrounding the solid xylem core can be 

 seen about three rows of phloem cells, some of the outer ones being small protophloem 

 elements. The large ones lying inside are presumably sieve tubes. A single layer 

 of rather large pericycle cells separates the phloem from the large endodermal cells, 

 which begin to show very conspicuously lignified radial thickenings, especially on 

 the side of the bundle adjacent to the second leaf trace. The section of the second 

 leaf trace is somewhat extended transversely and the xylem band is composed of 

 about a dozen tracheids. In the mid region of the section the xylem is separated 

 from the inner side of the bundle by a single layer of cells, possibly sieve tubes, but 

 at one point the xylem is in contact with the pericycle, which is only imperfectly 

 developed and wanting at certain points. Upon the dorsal side the phloem may 

 be in direct contact with the endodermis, which is quite wanting at this point upon 

 the ventral side of the bundle. Higher up, where the trace is quite free, the endo- 

 dermis extends completely around it. While the second leaf trace, therefore, may 



