PTERIDOPHYTES 
177 
that is, by the fusion of 
lateral branches (p. 152). 
The sporocarp seems to be 
a modified leaf blade or 
blades enclosing a group of 
son (fig. 408) . In Marsilea 
the sporocarp is somewhat 
bean-shaped, each sorus 
being in a cavity that ex- 
tends from the ventral side 
towards the dorsal (fig. 
409). Lining each cavity 
is a delicate indusium com- 
pletely investing the sorus, 
which contains both micro- 
sporangia and megaspo- 
rangia (fig. 410). In the 
microsporangia all the 
mother cells function in 
producing microspores ; 
while in each megaspo- 
rangium only one mega- 
spore matures, as in the 
Salviniaceae. The sori are 
attached to a tissue which 
swells remarkably upon 
exposure to water, dragging 
410 409 
FIGS. 408-410. Marsilea: 408, inside of one of 
the " valves " of the sporocarp, showing the system 
of veins, the short branches supplying the sori; 
409, section through a sporocarp, showing the two 
rows of sori beginning to develop (terminal cell in each 
is a young megasporangium) ; 410, section through 
a young sorus, showing a developing megasporangium 
(cutting off tapetal cells) above, and a microspo- 
rangium initial appearing on each side below; the 
investing indusium is evident. After JOHNSON. 
the sori out, from the 
ventral side of the sporo- 
carp, attached to a muci- 
laginous ring formed of 
the swollen tissue (fig. 
411). In Pilularia the 
sporocarp is globular, 
four soral cavities ex- 
tending from the base 
towards the apex, the 
FlG. 411. Marsilea: the swelling mucilaginous ring . ... 
dragging out sori (indusia enveloping sporangia) from microsporangia 
the sporocarp. above and the megaspo- 
