FILIGES. 



375 



boine upon slender pedicels. Morphologically they are trichomes, 

 ■whicli undergo a special modification. Each sporangium is at first a 

 two-celled trichome ; the lower cell of whicli develops into the pedicel, 

 while the other becomes divided by partitions parallel to its surface 

 into outer cells, which develop into the sporangial wall, and an inner 



Fig;. ^\.—A9pidiwm Mlioi-maa, Ay a section of a leaf through a sorus ; s, 8. the 

 'Sporangia, borne upon an elevated mass of tissue, the receptacle ; ^, i, the indusium, 

 seen in section. JS, a section of a young sporangium, showing its central cell divided 

 into four ; r, one cell of the ring, the section being at right angles to its plane. O, a 

 sporangium nearly mature, seen laterally ; r, ?', the ring of the sporangium ; d, a 

 elanduTar hair — in the interior of the sporangium are seen the nearly ripe spores. 

 Magnified.— After Sachs. 



tetrahedral cell (the so-called central cell), rich in protoplasm ; from the 

 latter a number of spore mother-cells (twelve, according to Reess) are 

 formed, and from each spore mother-cell four spores arise (Figs. 361 

 and 262). In each sporangium some of the cells of the wall are devel- 

 oped into an elastic ring {annulvs), which extends part way around the 



