1898 | THE LEAF AND SPOROCARP OF PILULARIA 19 
in the same mannert as in many other families of the group, and 
had a petiole more like these same forms in the number of divi- 
sions of its segments (see Sadebeck ’7q). Pilularia, on the con- 
trary, has no lamina, and has a smaller number of divisions in 
the leaf segments, resembling in this respect certain petioles of 
Marsilia (Johnson ’98), where the number of sections is reduced 
below the normal. Again, the type of division in the cap- 
sule seems to be easily derivable from that of the leaf of 
Marsilia, for the interpolated section IV of the former seems so 
plainly to assist in pushing the marginal cell around to the ven- 
tral surface, that we can readily believe it to have been added to 
a leaf of this type for this particular purpose. When all of these 
facts are considered, it seems evident that, so far as the structure 
of the leaf indicates, Marsilia is the less modified of the two 
genera, and resembles the other leptosporangiate ferns more 
closely, while Pilularia has a leaf very much reduced from the 
ancestral type. Whether the capsule of Pilularia is derived from 
one with more numerous sori cannot, perhaps, be profitably dis- 
cussed until we know the details of development in such forms 
as Marsila polycarpa, or M. Aegyptiaca, and Pilularia minuta, 
where the number of sori is reduced in each genus below that 
in the forms already studied, but from my own study of P. 
Slobulifera and M. quadrifolia, 1 am inclined to think the capsule 
of the latter, like its leaf, is the more primitive of the two. It 
seems to me that detailed study of the leaf development through- 
out the Leptosporangiate may be expected to give more light 
on the exact affinities of the Marsiliacezw with the other families 
of the group. 
In the segments forming the stalk of the sporocarp the 
protoderm gives rise to epidermis and hypodermis, and the 
ground meristem to mesophyll and the irregular partitions sepa- 
rating the small air canals, while the procambium gives rise in 
section I to the vascular bundle and in the other sections to 
the ventrally placed stereome bundle. 
The remaining younger segments of the sporocarp are devoted 
to the formation of the capsule. In this region two of the ulti- 
