1898 ] THE LEAF AND SPOROCARP OF PILULARIA 21 
dorsal surface of the leaf, through forms like Adiantum, with 
sporangia near the edge on the same surface, to Lygodium, where, 
according to Prantl (?87), the sporangia actually arise from 
marginal cells, the transition to the Marsiliacezx, with several 
sporangia arising from each marginal cell, does not seem to be 
so very abrupt. The indusium of Lygodium also seems to have 
a striking resemblance to that of the Marsiliacee in some 
features of its development, and may repay further investiga- 
tion from this point of view. 
The axial vascular bundle entering the base of the capsule 
divides into two, one branch going to the right and the other to 
the left side of the latter. Each of these again divides, forming 
four branches, each of which furnishes the three main bundles of 
a sorus. The middle one of the three in each case develops a 
placental branch which connects with the placental bundle 
present in the axis of the placenta. The three bundles of each 
sorus fuse together at the tip of the valve, but there is no fusion 
of the bundles of the upper and lower sori on the same side 
like that found in Marsilia. 
The firm wall of the globular capsule of Pilularia is made 
up, like that of Marsilia, of an epidermis of thick brown-walled 
cells with trichomes and stomata scattered among them. Within 
this are two hypodermal layers, the outer of very thick-walled, 
regularly prismatic cells, and an inner layer of larger, more 
irregular, brown-walled cells. Across the base of the capsule 
is formed the thick basal wall, the outer layer of which is con- 
tinuous with and exactly like the outer hypodermis and has the 
same “light line” running through it. Near the dorsal side of 
the capsule there is a narrow slit through this wall, correspond- 
ing to the air passage which opens into the lens-shaped space 
in Marsilia, but, though a tissue similar to that found in this 
space is present in Pilularia, it is not cut off from the rest of the 
capsule by a duplication of the hypodermis. 
Just opposite the basal wall there is a depression in the dor- 
Sal surface of the sporocarp, and just below this, at the upper 
end of the stalk, is an outgrowth corresponding to the lower 
