Leaf and Sporocarp in Marsilia quadrifolia , L. 141 
from the outer, and that at either end of the capsule from 
all three meristem- layers. 
The walls of the capsule, including the vascular bundle- 
system. are developed entirely, or practically so, from the 
four sections in each segment dorsal to the marginal cell. 
Hence the two valves into which the capsule splits at bursting 
cannot be homologized with the divisions of the lamina, since 
these are developed from the numerous sections formed on 
both sides by the continued activity of the marginal cells. 
For this reason also any seeming similarity in the branching 
of the vascular bundle-systems of the two organs can have 
no meaning in the direction of homology. 
We have here then another reason, in addition to the one 
mentioned above in speaking of the mode of origin of the 
sporocarp from the petiole, for not believing with Goebel that 
it represents a single leaflet or pinna with its edges folded 
in to meet at the ventral margin of the capsule. And the 
same objections hold against other views involving a belief 
in the laminar nature of the valves, such as that of Russow 
and Btisgen, who regard the capsule as made up of two leaflets 
with ventral surfaces facing each other, or that of Campbell 
and Meunier, who compare it to a folded pinnate leaf with 
a sorus for each pinna. 
As far as developmental history gives any clue, the sporo- 
carp of Marsilia is homologous with the petiole only of the 
sterile branch of the leaf. But before adopting this unre- 
servedly we have to explain why there should be the marked 
difference in the development of the longitudinal vascular 
bundle in the two, especially in such very similar structures 
as the petiole and stalk. 
So far as we have light at present, then, we may consider 
the capsule as the swollen end of a petiole in which the 
marginal cells are devoted to the formation of the sporangia 
instead of a lamina. 
