357 
Cortex of Setaginella , Spr. 
to expose the inner surface of the cortex, and if the section be 
cleared, one gets an appearance similar to that represented at 
Fig. i, PL XVIII. The vertical walls of the innermost cortical 
cells are observed more or less clearly through thin glassy 
plates of quite irregular size and shape. They have occasion- 
ally smooth, but more commonly very ragged edges, from 
which shorter or longer cracks extend into the body of the 
plate. Frequently a large plate becomes cracked into several 
pieces, the cracks widening into narrow channels. The edges 
of these channels are as a rule sharply defined, but occasionally 
at their inner extremities they become very faintly marked, as 
though the plates at that point were of extreme thinness. 
This feature is represented in the central plate of Fig. i. Here 
and there areas occur which are quite uncovered by the 
deposit, but it is possible that in these situations the plates 
have been displaced in the preparation of the section. In 
a longitudinal section of the stem, prepared to show the edge 
of the plates, one finds that the above interpretation of the 
surface-view is the correct one, for the plates are seen to be 
of irregular thickness, in some places being as much as three 
times the thickness of the cell-wall they cover, in other places 
lessening in thickness very considerably and finally ending in 
an exceedingly delicate film, only distinguishable by its differ- 
ence in refractive index from the cell- wall below. Fig. 2 shows 
a portion of such a section. Through gaps left in the deposit 
the trabecular cells arise from the cortex ; the base of one of 
these is shown in the figure. 
In addition to the deposit to be found on the outer lacunar 
wall, there occurs what seems to be a similar mineralization 
both in the walls of the innermost cortical cells and on the 
swollen cells of the compound trabeculae. If a transverse 
section be prepared cleared and mounted in balsam, the 
deposit may be quite easily made out in both situations. 
In Fig. 6 one of the compound trabeculae of X. Martensite 
var. stoloniferae is represented. (The lower end of the figure 
is that next to the cortex, the upper is that next to the 
pericycle.) The mineral deposit in such a trabecula occurs in 
B b 2 
