THK YOUNG SPOROPHYTE 



79 



It is not impossible that the root traces may also contribute to some extent to the 

 development of this ventral portion of the stele. The xylem masses belonging to the 

 two leaf traces remain quite distinct for a long time, the one belonging to the older 

 trace being better developed than that from the younger one (fig. 52, A). The 

 metaxylem consists of scattered tracheids arranged regularly in an arc outside the 

 protoxylem of the older bundle, but there are a few scattered smaller ones lying in 

 the tissue separating the two primary xylems, so that, as we have seen, the bundle 

 may perhaps be described as mesarch, and not endarch as it is in Ophioglossum and 

 Botrychtum. 



The two xylems of the separate bundles are finally connected by intermediate 

 tracheary tissue, so that a nearly complete ring of wood is formed; but the xylem of 

 the older leaf trace is still clearly recognizable on account of its greater thickness. 

 In the section figured (fig. 52, C) there is no tracheary tissue yet formed inside the 

 protoxylem and there is a well-marked pith occupying the center of the stele. The 

 endodermis is now well developed and inside it are about two rows of pericycle cells. 

 I he protophloem is less conspicuous than in the younger stele and is best developed 

 in the outer portion of the older leaf trace. The rest of the phloem is made up of 



/ 



Fie. 53. 



A. Transverse section of apex of first root of Helminthostachys, showing a 



single tetrahedral apical cell. X200. 



B. Apex of a later tetrarch root, with apparently no single initial cell. 



thin-walled cells, the larger of which are presumably young sieve tubes. The section 

 is taken from a much older part of the stem and shows that the bundle has attained 

 practically the same condition as in the adult stem, except for the absence of the 

 inner endodermis. The central pith is surrounded by an unbroken ring of wood, 

 averaging about three cells in width. The outer part of the bundle is essentially 

 the same as in the one that has been described. 



The canal described by Gwynne-Vaughn for the older sporophyte is plainly 

 evident here and extends backward from the sheath cavity, appearing in cross- 

 section as a narrow cleft between the inner side of the leaf stalk and the internode 

 (fig. 49, D, v). It is evidently not a cavity in the cortex, but merely an imagination 

 of the epidermis, which is continuous with that of the inner surface of the stipular 

 sheath. 



A peculiar feature of the ground tissue in the young stem and petiole in Helmin- 

 thostachys is the presence of cells containing roundish bodies which stain very 

 strongly with Bismarck brown, and these cells closely resemble the tannin cells of 

 the Marattiaceae, with which they are probably homologous (fig. 49, 6"). Lang 

 figures these cells (Lang I, fig. 65), but makes no mention of them in his text. 



