Leaf and Sporocarp in Marsilia quadrifolia , L. 127 
The Sporocarp. 
The bean-shaped sporocarps of Marsilia quadrifolia are 
usually borne in pairs, the stalks of the two uniting below, 
as shown by A. Braun (TO), to form a common stalk joining 
the petiole of the fertile leaf on its inner side near the base. 
Occasionally but a single sporocarp is found, or two with 
stalks separately inserted on the petiole, or more rarely three 
or four, usually with a common stalk. In the half-grown 
sporocarp we find the smaller or younger one of the pair is 
borne on the side of the stalk toward the petiole. If sporo- 
carps occur on any leaves of a given branch they are usually 
found on all. 
Plants of Marsilia which were left out of water in September 
by the drying up of a pond, matured many more sporocarps 
than plants growing where the water-level was constant. 
Although the latter had an equal number of young sporo- 
carps in July, nothing but small and often shrunken rudiments 
were found on most of the plants in September ; these might, 
however, be borne on large and well-developed petioles, so 
that there is no regularity in the retardation in development 
of the fertile leaves. 
Bischoff (’28) says the sporocarp of Marsilia arises as a 
slight prominence on the anterior side of the petiole, while 
Mettenius (’46) states that it originates endogenously, and 
later breaks through the epidermis of the petiole to form 
a solid mass of tissue, in the interior of which later the sori 
and canals are developed. The youngest sporocarp studied 
by Russow (72) had a two-sided apical cell, but was already 
differentiated into stalk and capsule (probably about the stage 
of that shown in Fig. 42 ). He thought the soral canals arose 
by the splitting apart of certain cells in the interior of the 
capsule and the formation of pits on the ventral surface into 
which these slits opened, to close again later by the growth 
of the cells on the ventral surface. On the walls of these 
canals arose the ‘ soral cells,’ in each of which later a tetra- 
