DEVELOPMENT OF PLANTS 



295 



tected by a membranous outgrowth of the epidermis, known 

 as the indusium (Fig. 222, B). Each sporangium originates 

 usually from a single epidermal cell, which by repeated divisions 



FIG. 223. Section of a leaf of Woodwardia, showing two sori : i, in- 

 dusium; sp, sporangia arising from the epidermis and in various stages 

 of development. Note the epidermis, stoma, s, palisade and spongy chlo- 

 renchyma, and vascular bundles, as in higher plants. 



(Fig. 223) produces a capsule or sporangium that varies con- 

 siderably in structure in the various genera. In the simplest 

 forms, it consists of a uniform layer of wall cells inclosing a 

 mass of cells, the majority of which become spore mother cells, 



FIG. 224. Character of sporangia: A, simple type of sporangium of 

 Osmunda with rudimentary annulus, an, of a few thickened cells. B, com- 

 mon type of sporangium an, annulus ; I, lip cells. 



producing four spores each. In other cases, a few of the wall 

 cells are thickened, forming a rudimentary annulus ( Fig. 224, A ) . 

 but in the majority of our common ferns, the sporangium con- 



