1922| BROW NE—EQUISETUM 453 
of two endodermal sheaths are replaced by single endodermal 
cells, common to both bundles. A little higher still these single 
endodermal cells are replaced by nodal tracheids, and the special 
endodermes by the common inner and outer endodermes typical 
of the vegetative nodes throughout Eguisetum. When a branch 
is to be given off, the inner endodermis projects outward in a loop 
inside the arch of xylem representing the outer, lower insertion of 
the ramular siphonostele (fig. 2, stage 8b). In such a case the 
endodermal cells at the inner narrow end of the loop fuse before 
the junction of the nodal tracheids in this region. The endo- 
Fic. 3.—Stages 9-11; br.x, es i branch; b.end, endodermis of branch; other 
lettering as in figs. 1 and 2; X about 
dermis of the branch is thus in continuity with the inner endodermis 
of the axis. 
To return to the carinal canals, these dwindle rapidly after the 
nodal tracheids have spread over the parenchymatous sheath, 
and soon disappear. As most of the medianly situated protoxylem 
tracheids have departed into the leaf, this region consists chiefly 
of parenchyma, in which are sometimes found a few tracheids that 
die out as we pass upward. A few of the protoxylem elements, 
however, forming the upward continuation of the elements at the 
sides of the carinal canals, may be seen persisting as two little 
groups on each side of the parenchymatous sinus that replaces 
the carinal canal. At the same time the parenchymatous depres- 
sion in the outer edge of the nodal wood, opposite the departing 
trace, deepens, as is shown in fig. 3, stages 9 and 10. Meanwhile 
the inner endodermis becomes involuted into the parenchymatous 
