3560 BOTANICAL GAZETTE [MAY 
frequently a cambium develops and produces tracheids in definite 
radial rows (fig. 12). The cambium usually occurs on the inner 
side of the xylem, but in a few cases it is located on the outer side, 
and sieve tubes occur between it and the endodermis. 
The endodermis.—A well marked external endodermis is con- 
stantly present in all species of Botrychium that were examined. 
The suberized band on the radial walls is particularly heavy in 
B. virginianum and B. obliquum. In uninjured rhizomes of these 
two species, the external endodermis is continuous except at the 
points of departure of leaf traces. As a trace swings out from the 
stele, the endodermis breaks at the side of the trace and closes again 
rather higher up across the leaf gap; the endodermis on the abaxial 
side of the trace persists for a short distance only. In injured 
rhizomes of these two species, the irregular growth of the various 
stelar tissues has produced distortions and breaks of the endodermal 
layer (fig. 6). In these specimens, the cells of the endodermis fre- 
quently divide by periclinal walls; but there is no evidence that 
vascular elements are ever formed as a result of this growth. In no 
case were vascular elements found definitely outside the external 
endodermis. The only internal endodermis found was that occa- 
sionally formed by the folding in of the margins of the external 
endodermis in cases of greatly disturbed steles (fig. 6, GC): 
Discussion.—The occurrence of scattered tracheids in the pith 
has been observed in B. ternatum by Bower (r) and in B. Lunaria 
by Lane (9). As stated above, both scattered tracheids and dis- 
tinct secondary xylem occur frequently in the pith of injured 
rhizomes of B. virginianum and B. obliquum. The occurrence of 
well organized strands of xylem in the pith of a rhizome of Ophio- 
glossum pendulum has been reported by the writer (10). In view of 
these facts, it may be concluded that the pith is definitely stelar in 
character in Botrychium and probably in all three genera of the 
family. 
_A slight intrusion of cortical tissue might occur at the point of 
the break of the endodermis without affecting the pith; such an 
intrusion would affect only the tissues between the leaf trace and 
the leaf gap. It may be pointed out that in branching specimens 
of B. ramosum, B. virginianum, and B. obliguum, xylem is produce 
