PTLI0E8. 



375 



boine upon slender pedicels. Morphologically tliey are trichomes, 

 which underjio a special modification. Each sporangium is at first a 

 two-ceiled trichome ; the lower cell of which 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 



■pig. 281.— .4sp2(?iMm MUx-mas. A, a section of a leaf through a sorns ; s, », the 

 sDorangia borne upon an elevated mass of tissue, the receptacle ; i, i, the indusium, 

 seen in section. £, 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. C. a 

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

 glandular 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 363). In each sporangium some of the cells of the wall are devel- 

 oped into an elastic ring [annulus), whicli extends part way around the 



