1920J CRIBBS—TODEA BARBARA 285 



of the foot in a three-leaved sporophyte is shown in fig. 26, and it 

 will be noticed that it almost caps the foot tissues at this early 

 stage, only two cells remaining free. Throughout all the stages, 

 so far as studied in the young stem, there was no indication 

 whatever of the endodermis dipping into the stele; but in complete 

 continuity it passes over the gaps in the xylem caused by the 

 departing leaf traces, without the slightest tendency to invaginate. 

 A commonly recurring feature of the endodermis from about the 

 level of the sixth leaf trace was the absence of storage materials 

 opposite leaf gaps. Frequently there was likewise an absence of 

 storage in the pericycle at the same point. Across this gap in the 

 storage material, however, the endodermis was always found to be 

 continuous. 



The origin of the pericycle from the stem apex is difficult to 

 determine, and it could not be definitely referred to initials which 

 would point to a common origin with the endodermis. For the 

 most part the pericycle cells contain an abundance of finely 

 granular resinous material. As has already been pointed out, the 

 pericycle does not form a complete circle in the earliest stages of 

 the stele, but is interrupted at many points. At the level of the 

 sixth or eighth trace it is rarely more than one cell thick, and in 

 the young sporophyte it seldom exceeds two cells in thickness 

 except at the edge of root attachments and in the adaxial angle of 

 the leaf traces, where it frequently becomes very prominent (figs. 3, 

 44), and, like the endodermis, is quite regularly filled with finely 

 granular material or with larger granules similar to those of the 

 storage cells in the sheath parenchyma and medulla. The peri- 

 cycle is increased in thickness by periclinal divisions (fig. 1), but 

 the so-called "quergestrickten Zellen" of the older stem which 

 have their origin in this way do not appear prominently in the 

 earliest stages, but appear much more abundantly after the develop- 

 ment of a central medulla. 



There is a paucity of sieve cells in the lower levels of the stele, 

 where they are most prominently and regularly developed on the 

 outer edge of the xylem elements which are about to turn out from 

 the cylinder as traces. The sieve cells are elongated elements 

 terminated by oblique walls. The radial, terminal, and likewise the 



