176 



MORPHOLOGY 



Fig. 407. — MarsUea: showingdorsiventral stem giving 

 rise to roots below and leaves above, circinate vernation 

 of developing leaves, and adaxially borne sporocarps. 



Marsileaceae 



This family comprises 

 the genera MarsUea and 

 Pilularia, whose species 

 root in the mud, under 

 water or in muddy flats. 



Sporophyte. — The 

 stem is dorsi ventral, 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 MarsUea 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 ; 



