540 A TEXTBOOK OF THEORETICAL BOTANY 



is sterile and bears a lamina which is divided on each side of the rachis into 

 six to eight kidney-shaped pinnae with branching veins. The fertile segment, 

 which is attached at the base of the sterile one, has no lamina and consists 



Fig. 539. — Botrychium hmaria. Two plants show- 

 ing fertile and vegetative leaf segments. About 

 half size. 



of a rachis bearing two ranks of pinnately arranged appendages, on each of 

 which are two parallel rows of sporangia. Normally only one such leaf is 

 produced each year. 



Anatomy of the Stem 



The stem grows from a single apical cell, which is sunk beneath a covering 

 of successive leaf rudiments, each leaf apparently corresponding to a segment 

 formed by the apical cell. The leaf of the current year has a completely 

 sheathing base, which surrounds the stem apex like a tube. Inside this is the 

 leaf for the next year, with sterile and fertile segments already formed (Fig. 

 540). There is no circinnate arrangement of the young leaves as in other 

 Ferns. Two or three other leaf rudiments for future years may also be 

 present. The basal sheath of the embryonic leaf is split into two portions, 

 a division which remains even in the mature leaf of B. virgimamim and 

 suggests that this sheath is formed by the fusion of two stipules such 



