Boodle. — Anatomy of the Gleicheniaceae . 705 
but with a bud at the fork, which may continue to grow 
for a time as a main rachis, and then repeat the process o 
forking and production of a terminal bud. Thus many pairs 
of primary pinnae are formed, and their mode of growth may 
be identical with that of the main rachis. The pinnules are 
borne in a pinnate manner. Diagrams illustrating the leaf- 
form in the different sections of the subgenus Mertensia are 
given by Diels (’ 00 , p. 353)- The dichotomy of the primary 
pinnae, and the production (at the fork) of a bud, which after- 
wards develops as a secondary rachis, and the pinnate arrange- 
ment of the pinnules, are all characters which are also found 
in species of Lygodium. Further, in G. pectinata after the 
first dichotomy the rachis, which is perhaps a sympodium, 
bears pinnae singly, and as the latter are short and forked 
there is a close agreement with what is found in Lygodium. 
G. moniliformis and G. simplex , both of which appear to 
be reduced forms, have simple pinnatipartite leaves. Ex- 
cluding these, dichotomy in the leaf is a character of the 
genus. It is a primitive character which is shared by species 
of Lygodium , Schizaea and Gleichenia. It may be pointed 
out as quite possible that the pinnate form of leaf, as found 
in Anemia and perhaps in some other groups of Ferns, may 
have originally been derived from a dichotomous form of 
leaf, like that of Gleichenia , the pairs of primary pinnae 
representing dichotomies, and the rachis representing the 
products of a series of buds formed in the successive forks. 
In other cases a pinnate leaf may occur in a dichotomous 
type, apparently by suppression of dichotomy, what would 
be the ultimate branches of the leaf being borne directly on 
the petiole. 
Numerous forms of hairs and paleae occur on the rhizome 
and leaf. 
Gleichenia, rhizome. 
In the majority of the species of Gleichenia the rhizome 
has a uniform type of structure in the internode, namely, 
a centrally placed solid stele (protostele), consisting of a 
central mass of xylem, composed of tracheides and paren- 
