Leaf and Sporocarp in Mar si li a quadrifolia , L. 135 
In horizontal section it is seen that the three middle or 
sporangial cells become more densely filled with protoplasm 
than the indusial cells (Fig. 35), and also become separated at 
the ventral surface from the cells of section V (s. c Figs. 29, 
35), thus forming the beginning of the soral canal. Otherwise 
the development of all of the five cells is much alike at first, 
and if we take transverse sections in the plane of the sporangial 
cells, we find that each elongates considerably in a radial 
direction (Fig. 39), and later divides into two by a pericline 
(Fig. 30). Then by the further growth and division of both 
of these cells ( ma.-sp . m. c Fig. 31), there is formed a row of 
seven or eight cells reaching from about the centre of the 
capsule nearly to the ventral surface (Fig. 32), all of them 
separated by the soral cavity or canal from that part of the 
indOsium formed from section V. In sagittal section (Fig. 43) 
it is seen that the microsporangial and indusial cells have 
divided in a similar manner. 
From the occurrence in them of nuclear spindles and their 
relation to the surrounding cells;, there can be no doubt that 
all the sporangial cells of the sorus are derived from the 
marginal cell, and none from cells dorsal to this in the interior 
of the capsule, as Biisgen thought possible. In the bending of 
the soral canal that takes place as it increases in length, the 
sporangial cells may come in contact with the inner layer 
of the indusium, but there is certainly no growing together, 
and the phenomenon has no significance. It is during the 
development of this row of soral cells that they are outgrown 
and finally enclosed by the surrounding cells, forming at first 
a ‘funnel-like pit’ at the ventral end of the soral canal 
(Figs. 30, 31), but finally closing entirely, though leaving 
traces of the fusion for a long time (.y. c. } Figs. 32, 33). 
While the sporangial and indusial cells have increased in 
numbers by the radial growth and division, there have been 
other important changes. The- macrosporangium mother-cells 
( ma-sp . m. c ., Figs. 35, 36) are pushed by the growth of the 
plerome of section VI ( pa . b., Figs. 36, 37) out into the soral 
cavity, far beyond the microsporangium mother-cells, swell 
L 
