202 CAT>lFORNIA ACADEMY OF SCIENCES. 



The embryo of Marsilia shows the closest resemblance 

 to that of Pilularia, but also agrees closely with that of 

 the Polypodiace^, with which we have also seen it agrees 

 in the principal points of the development of the sexual 

 organs. 



THE SYSTEMATIC POSITION OF THI-: MARSIEIACE^. 



A comparison of the Marsiliacect with the other Pteri- 

 dophytes will show at once such striking resemblances to 

 the leptosporangiate ferns as to leave no room for doubt- 

 ing the close relationships of these groups. This is seen 

 in the tissues and growth of the mature sporophyte. The 

 leaf, stem and root, grow in the same way as in the Poly- 

 podiacea^ and the leaves also have the peculiar circinnate 

 vernation of the ferns, which is absent in the Salviniace;e. 

 The structure of the fruit, too, upon which some stress 

 has been laid is simply a peculiar modification of the 

 leaf, developed as other parts of the plant have been, 

 probably, in response to special conditions. The de- 

 velopment of the sporangia, too, agrees in the principal 

 details with the Polypodiacea^, and the early divisions of 

 the embryo correspond almost exactly with the embryo 

 in that group. With the Salviniacea there is little in 

 common, and botanists have long recognized this fact, 

 although grouping them together for the sake of con- 

 venience, as both are obviously related to the homo- 

 sporous leptosporangiate ferns. 



We must bear in mind, however, that in the Marsiliacea? 

 we have to do with a very much specialized group, which 

 has no immediate relations ; and we should naturally ex- 

 pect to lind this indicated in some way. Of the two 

 genera, Pilularia comes nearer the Polypodiacese in sev- 

 eral particulars. There are often two vegetative cells in 

 the male prothallium, and the structure of the antheridium 

 and spermatozoids departs less widely from the type found 



