FILICINEM. 



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 line 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 little is known concerning the de- 

 velopment of the sporangia in other families 

 of Ferns. According to Russow and Prantl 

 it takes place in Alsophila (Cyatheaceae) in 

 the same way as in the Polypodiaceae, whilst 

 in Aneimia and Mohria (Schizseaceae), 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 Schizseaceae. In both 

 families a much larger number of spore- mother-cells is formed in the sporangium 

 than is the case in the Polypodiaceae, and this fact also recalls the Ophioglosseae 

 and the Marattiaceae. 



Each spore-mother- cell is, in Aspidium 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 (/F), the 

 mother-cell splitting up into four spore-cells (F), the relative position of which 

 varies (as is shown in Figs. F/, 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 the sporangium of Asple- 

 nium Trichonianes ; 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 55o)- 



