18 BOTANICAL GAZETTE [yury 
by the outgrowth of surface cells favors the opposite view, as 
has been pointed out by Meunier. 
SUMMARY AND CONCLUSIONS. 
The leaf of Pilularia develops, like that of Marsilia and many 
other leptosporangiate ferns, by a two-sided apical cell arising 
on the right and left sides alternately of the dorsal surface of 
the stem, near the apex. 
The eleven or more pairs of segments formed by this apical 
cell divide primarily into three sections and a quaternary mar- 
ginal cell, instead of five and a marginal cell of the sixth grade, 
as in Marsilia. Each of these four divisions takes part in the 
formation of all three meristem layers. The sheath of the axial 
bundle is derived from the procambium and not from the ground 
meristem as in other ferns. The mesophyll of the mature leaf 
is of a single layer. Outside of this are the ten air canals, sepa- 
rated both laterally and transversely by perforated partitions, and 
surrounded externally by the epidermis and epee dees 
oped from the protoderm. 
No indication of a rudimentary lamina could be found 
carefully following the details of division in the terminal se‘ 
ments of the circinately coiled leaf. 
The sporocarp of Pilularia is a branch of the leaf, arising if 
an anterior marginal cell at the base of the latter. It eee | 
a two-sided apical cell which cuts off six or more pairs of s 
ments, and is then divided up by irregular anticlines. Thes 
segments, like those of the sporocarp of Marsilia, form } 
primary divisions. 
This plan of division found in both genera must, + think 
regarded as a characteristic of the spore-bearing portion of : 
leaf in their common ancestor. From the absence 0 
