128 Johnson. — On the Development of the 
hedral apical cell was formed, which cut off a number of 
segments that, according to Russow, gave rise to the placenta 
with its vascular bundle and to the microsporangia, while 
the apical cell itself finally became the macrosporangium. 
Goebel (’ 82 ) states that the soral canals of Marsilia are 
external in origin, and that the sporangia arise from super- 
ficial cells ; Blisgen (’ 92 ) describes the first rudiment of the 
sporocarp as ‘ eine scheinbare grosse Liicke ’ in the tissue of 
the young leaf, and he thinks it probable that all the soral 
cells of each sorus are derived from a single superficial cell 
of the ventral surface. The placenta, microsporangia and 
macrosporangia, he states, are formed as Russow has described 
from these soral cells. 
According to my own observations on M. quadrifolia , the 
sporocarp makes its appearance when the young fertile leaf 
consists of about six or seven pairs of segments, and thus 
long before the appearance of the lamina. It is developed 
from an apical cell exactly like that of the leaf, formed in one 
of the ultimate marginal cells of the inner side of the petiole 
(F. m. c., Fig. 22) and placed transversely to the latter. The 
marginal cell involved may be either the upper or lower of 
(apparently always) the second segment of the inner side 
of the petiole, though, because of the crowding together of 
the various rudiments of the bud, this could not be made out 
with certainty (F., Fig. 23). The sporocarp is thus not, 
strictly speaking, epidermal in origin, but resembles closely 
in its origin the single sporangium of Lygodium from a mar- 
ginal cell of the fertile pinnule, as described by Prantl (’ 81 ). 
The apical cell of the sporocarp thus formed goes on 
cutting off segments, alternately toward the base and apex 
of the leaf, or to the right and left of the sporocarp itself, 
until about twenty-three pairs of segments are formed. It 
thus gives rise to a papilla, much like the very young leaf, 
which bends laterally to grow up beside the petiole with its 
ventral side facing in the same direction (Fig. 24), and then 
bends ventrally upon itself at the point where the stalk joins 
the capsule (Fig. 25). Finally, at about the time that the 
