5 1 2 Boodle . — Comparative Anatomy of the 
for special description. These are: dichotomous branching, 
nodal endodermal pockets, internal endodermis, and internal 
tracheides. 
i. Branching. Among the specimens of .S'. dichotoma there 
were two or three with branched rhizomes. The branching 
has every appearance of being dichotomous, both on external 
examination and also in the behaviour of the stele. When 
preparing for dichotomy 
the stele becomes elong- 
ated in the horizontal 
plane and then divides 
into two in a simple 
manner 1 . Three stages 
of its division are shown 
in Fig. 24. In this series, 
after the elongation of 
the stele, a leaf-trace is 
given off on the upper 
side leaving a gap in the 
xylem and phloem, which 
becomes very wide (Fig. 
24, A); the lower part 
of the band of xylem and 
phloem splits in the me- 
dian plane ; the endo- 
dermis becomes con- 
stricted and fuses in the 
same plane (Fig. 24, B ), 
producing an hour-glass- 
shaped double stele, 
which then separates 
into two by fission of the endodermal bridge at the neck. 
The dichotomy of the stele is thus complete (Fig. 24, C). 
No branching other than apparent dichotomy was observed. 
The mode of division of the stele (assuming that the latter 
1 Internal endodermis and internal tracheides may be present in the region 
of dichotomy, but do not affect the mode of division of the stele. 
Fig. 24. — Dichotomy of the stele of S. dicho- 
toma. A, B, C, three stages in acropetal order, 
x 9. Endodermis represented by bounding 
line ; xylem cross-hatched ; phloem shown as 
a broken line. In C, leaf-trace and root at l.t. 
and r. 
