FI L I CI NE ^. 
437 
by intercalary transverse divisions and longitudinal walls, into three rows of cells ; 
the nearly hemispherical mother-cell of the capsule is next transformed, by four 
successive oblique divisions, into four plano-convex parietal cells and a tetrahedral 
inner cell (archesporium) ; in the former further divisions follow perpendicular to 
the surface, while the inner cell again forms 
four tabular segments which are parallel to 
the outer parietal cells and which constitute 
the tapetum. These inner parietal cells also 
divide perpendicularly to the surface of the 
capsule, and may form two layers. The cells 
of the outer parietal layer from which the 
annulus is to be formed are further divided 
by parallel walls perpendicular to the surface 
of the sporangium and to the median hne of 
the annulus, until the prescribed number of 
cells of the annulus is reached ; these cells 
then project above the surface of the capsule. 
While the tetrahedral central cell is now pro- 
ducing the mother-cells of the spores by suc- 
cessive bipartitions, the cells of the tapetum 
are absorbed, and the cavity of the sporan- 
gium is considerably enlarged by this means 
and by the superficial growth of the outer 
parietal layer ; so that the mass of mother- 
cells (according to Russow there are usually 
sixteen) floats entirely free in the fluid that 
fills the sporangium (Fig. 304). 
But Httle is known concerning the de- 
velopment of the sporangia in other families 
of Ferns. According to Russow and Prantl 
it takes place in Alsophila (Cyatheacese) in 
the same way as in the Polypodiaceae, whilst 
in Aneimia and Mohria (Schizseacese), accord- 
ing to their figures and descriptions, each sporangium arises, before the differen- 
tiation of the epidermis, from a single cell. Probably the sporangia of the 
Osmundacese originate in the same way as those of the Schizaeaceae. In both 
families a much larger number of spore-mother-cells is formed in the sporangium 
than is the case in the PolypodiaceEe, and this fact also recalls the Ophioglosseae 
and the Marattiaceae. 
Each spore-moLher-cell is, in Aspidiiim Filix-mas (Fig. 306, /), provided with 
an evident nucleus ; in consequence of its division, two new large clear nuclei 
arise (///), between which an evident line of separation is sometimes to be seen. 
After the division of these nuclei, four new smaller nuclei appear {IV), the 
mother-cell splitting up into four spore-cells (F), the relative position of which 
varies (as is shown in Figs. VI, VII, and VIII), The spore now becomes clothed 
with its cell-wall, which is differentiated into an endospore consisting of cellulose 
Fig. 305. — Development of tlie sporangium of Asple- 
nucm Trichomanes ; the order of succession according- to 
the letters a-i; in i the annulus r is shown ; the other 
figures are seen in optical longitudinal section, and the an- 
nulus is perpendicular to the plane of the paper (X 55°). 
