Leaf and Sporocarp in Marsilia quadrifolia , L. 133 
of section III, and from a part of the same region of 
section IV (/. b., Figs. 29, 31, 32). Of the two outer forks 
of this bundle one arises in the basiscopic quarter of the 
acroscopic half of the plerome of the same segment (/. b.f, 
Figs. 35, 39, 40), and the other from the acroscopic quarter of 
the acroscopic half of the next older segment. These forks 
are formed very early, but grow in length with the sorus, and 
finally on beyond it to the ventral edge of the capsule 
(Figs. 33-44), where their ends become connected in a more 
or less regular way with those of their fellows of the same 
side of the capsule (/. b.f., Fig. 44). The third or placental 
branch of the lateral bundle arises from a part of the plerome 
of the basiscopic half of section VI (pa., br., Figs. 31, 32, 33, 
42), and the placental bundle with which this connects is 
developed from the plerome of the same part of this section 
(pa., b., Figs. 30, 32, 36, 41, 42). 
The Sori. 
Of the sections on the ventral side of the marginal cell, the 
plerome of section II develops ultimately into the large-celled 
tissue of the dorsal portion of the gelatinous ring (pi. 2 , 
Figs. 29, 31 ,g. r., Figs. 32, 33), described by Hanstein (’62) 
and Russow. The plerome of section V grows around under 
the inner end of the marginal cell (Figs. 28-32), and probably 
takes part ultimately in the formation either of the gelatinous 
ring or perhaps of the stalks by which the indusia are attached 
to the latter, but this was not determined with certainty. 
The periblem of both these sections apparently develops very 
slightly, and seems to form a part of the stalk of the indusium 
(pb., Figs. 28-31), but the boundary between this and the 
dermatogen soon becomes indistinguishable. The dermatogen 
of both sections grows rapidly in a radial direction (d., Figs. 
28-31, o. ind., Figs. 32, 33), and gives rise to that portion of 
the indusium on the median side of the sorus. The outer or 
ventral cells of these sections soon grow over laterally to 
meet section VI, and thus enclose the cells of the sorus, 
while certain cells of these just below the ventral wall give 
