21 8 



THIRD GROUP. VASCULAR CRYPTOGAMS. 



the Ferns which have been examined as that which will now be described for the 

 Polypodiaceae 1 . The sporangium originates in a papilla-like outgrowth of one of the 

 epidermal cells which give rise to the sorus. The papilla is cut off by a transverse 

 wall, and becomes the mother-cell of the sporangium ; after further elongation a 

 transverse wall next divides it into a lower cell which produces the stalk and an upper 

 which becomes the capsule of the sporangium. The stalk-cell is transformed by 

 intercalary transverse divisions and longitudinal walls usually into three rows of cells ; 

 the nearly hemispherical mother-cell of the capsule is first divided by four successive 

 oblique walls into four plano-convex outer cells which form the outer wall, and a 

 tetrahedral inner cell, the archesporium ; further divisions perpendicular to the surface 



then appear in the cells of the outer wall, 

 while the archesporium forms four tabular 

 segments, which lie parallel to the outer 

 cells forming the wall ; these inner parietal 

 cells divide in planes at right angles to 

 the surface of the capsule, and may even 

 separate into two layers which together 

 form the tapetum. The cells of the wall 

 which are to form the annulus further 

 divide by septa which are perpendicular to 

 the surface of the sporangium and to the 

 median line of the annulus and are 

 parallel to one another, till the proper number of the cells of the annulus is obtained ; 

 the cells then become convex outwards and project above the surface of the capsule. 

 Then while the tetrahedral archesporium forms the mother-cells of the spores by 

 successive bipartitions, the cells of the tapetum are dissolved, and the inner space 

 of the sporangium is considerably enlarged by this means and by the surface 

 growth of the outer wall, so that the mass of the spore-mother-cells, the number 

 of which according to Russow is usually sixteen, floats free in the fluid which 

 fills the sporangium (Fig. 164). 



Every spore-mother-cell has a distinct nucleus (Fig. 166 7) 2 , the division of 

 which produces two new nuclei ; each divides again, and so four new smaller nuclei 

 are seen (Fig. 166 IV] ; the mother-cell thereupon breaks up into four spore-cells, 

 (V), the relative position of which varies, as appears from VI, VII, VIII; next the 

 spore is invested with a membrane, which becomes differentiated into an endosporium 

 showing the reaction of cellulose in Osmunda and other genera, but not in Gleichenia 

 and some others, and a brown cuticularised exosporium with ridges on its surface ; the 

 contents of the spore form chlorophyll in the Osmundaceae and Hymenophyllaceae. 

 In various other Polypodiaceae the course of formation of the spores according to 

 Russow runs somewhat differently ; the mother-cell divides into four rather thick- 

 walled compartments, the so-called special mother-cells, as in the formation of pollen 

 in the Phanerogams, whereupon the protoplasm of each compartment becomes 



FIG. 166. Development of the spores of Asfidium Filix- 

 mas ; magn. 550 times. See the text. 



' Sporangia are found in every stage of development in the same sorus. 



' The figure was drawn when the circumstances connected with the division of the nucleus 

 were not yet known, and its details therefore are not shown in 77, 777, and IV. 



