1911} CHARLES—ANATOMY OF MARATTIA 89 
The course of the medullary system is relatively uniform in 
different stems. The strand runs upward through the medulla 
toward a leaf gap that is about to close (fig. 25). It joins one of 
the margins of the gap, the strand on the other margin closes in, 
and the three strands form 
a plate of vascular tissue 
from whose outer surface 
a root usually goes off 
(fig. 25, rt). The medul- 
lary strand soon frees it- 
self again while a leaf trace 
goes off from the vascu- 
lar plate above the point 
where the medullary 
strand joined the main 
vascular system. Farther 
on in its course the medul- 
lary strand sends a short 
branch into the main sys- 
tem, and this is not given 
off again but goes out with 
a leaf trace (fig. 25, ms). 
As the leaf traces become 
more crowded (text fig. 
2a) the medullary strand 
dividesinto a greater num- 
ber of parts, which join the 
main system at the clos- 
ing of the leaf gaps. Oc- Frc. 2a.—Exterior view of diagram model of 
: the stele at the stage when the medullary strand 
casionally a gap closes appears; the medullary strands can be seen 
without a strand from the through the upper leaf gap. 
medullary system. At 
this stage Kaulfussia (1'7) and Archangiopteris (12) closely resemble 
Marattia. 
Further complications of the medullary system of Marattia come 
from combinations of anastomoses and branching (text fig. 3). In 
Matonia the second cylinder is developed from the solid central strand 
