356 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 

 caM. 1 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, C). 



Discussion. — The occurrence of scattered tracheids in the pith 

 has been observed in B. Icrnatum by Bower (i) and in B. Lunaria 

 by Lang (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 Opl/io- 

 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, ami B. obliquum, xylem is produced 



