350 BOTANICAL GAZETTE [MAY 
between the two (figs. 4, B, and 7). At first these extend the entire 
distance between the two and give the appearance of expansion of 
the stele in the plane of the leaf trace; but later they separate from 
the stem stele, as shown by fig.4,C. These wings may be considered 
to be adaxial extensions of the centrifugal xylem of the leaf trace; 
there is at no point any evidence of centripetal xylem. Soon after 
the separation from the stem stele, the leaf trace disappears, having 
been cut off by the absciss layer and carried out by periderm forma- 
tion. This leaves two distinct wings of xylem and each of these 
Fic. 4.—Transverse sections of a branching rhizome of Boirychium ramosum; 
X12. 
by extension of its margins rounds up into a definite branch stele, 
as shown in figs. 4,D, E,F, and 8. One of these branch steles 
soon disappears, having apparently been unable to meet the com- 
petition; its apical region has been entirely obliterated by pet 
derm formation. There can be little doubt that both these branch 
steles developed from a single axillary bud. 
In the other branching specimen of this species, a wing of 
xylem extends between the leaf trace and the stem stele on one 
side only. It separates from the stem stele and at a slightly higher 
point the leaf trace disappears. By extension of its margins, te 
