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MORPHOLOGY 
FIG. 407. Marsilea : showing dorsiventral stem giving 
rise to roots below and leaves above, circinate vernation 
of developing leaves, and adaxiully borne sporocarps. 
Marsileaceae 
This family comprises 
the genera Marsilea and 
Pilularia, whose species 
root in the mud, under 
water or in muddy flats. 
Sporophyte. The 
stem is dorsiventral, as 
in the Salviniaceae, but 
it develops from an 
apical cell with three 
cutting faces, thus form- 
ing three longitudinal 
rows of segments. The 
leaves alternate from 
the dorsal segments, and 
the roots are produced 
by the ventral segments. 
The leaf of Marsilea has 
a long petiole and four 
leaflets peltately ar- 
ranged (fig. 407) ; the 
first leaves, however, 
produce no blades, only 
the petiole developing, 
and this is the permanent 
condition in Pilularia. 
Sporocarp. The so- 
called sporocarp is borne 
on a stalk that arises 
adaxially from the leaf 
(petiole) , the whole struc- 
ture apparently being a 
spore-bearing branch of 
the leaf (fig. 407). This 
adaxial structure may 
have arisen as did that 
of the Ophioglossales; 
