of the Anatomy of the Genus Selaginella , Spr, 179 
Considering first a branch axis, one finds above the first 
branch a single ribbon-shaped stele with two marginal protoxy- 
lems, the leaf-traces being, as in the monostelic forms, inserted 
on these. Where this secondary axis receives a tertiary, the 
mode of union of the steles is fundamentally similar to that 
seen in the ordinary monostelic type. The inner marginal 
protoxylems unite to form a dorsal cord, which fuses lower 
down to form with the outer marginal cord of the tertiary 
branch the marginal strand of that side of the axis beneath. 
The axillary leaf-trace inserts itself just at the junction of the 
inner protoxylems. Lower down, however, this strand becomes 
strengthened by a few tracheids from the united marginal 
protoxylems, and tends to form a distinct ventral cord quite 
similar to that formed by the united marginal protoxylems 
themselves. These cords presently separate from the median 
stele, just as in S. uncinata , and in section one gets three 
steles, the median with two protoxylems, the dorsal and 
ventral with one each. 
If we now endeavour to trace the mode of fusion of a branch 
which possesses a median stele with a dorsal stele still in the 
condition of a dorsal cord and a ventral isolated stele, with 
a more vigorous axis having a ventral stele with two proto- 
xylems, a median stele with two protoxylems and a dorsal 
cord like that described in S. uncinata , the course of fusion 
is found to be as follows The dorsal cord of the main 
axis fuses with that of the secondary to form a distinct dorsal 
stele with two protoxylems ; these, however, unite with one 
(the outer) marginal protoxylem before fusion with the next 
lower dorsal cord (cf. S. flahellata) y which in its turn forms 
the outer marginal protoxylem of the dorsal stele. The outer 
marginal strand of the median stele of the chief axis remains 
as the marginal strand of that side of the median stele of the 
axis beneath. The inner marginal strand of the median stele 
of the chief axis forms a connexion with, first, the inner mar- 
ginal protoxylem of the ventral stele of the chief axis, but 
separates almost at once ; secondly, with the ventral cord of 
the branch-axis, also separating again immediately ; and, 
