326 SPORANGIA OF FILICALES 



leaves. Therefore, Bower estimates that the shield fern produces 

 annually upwards of 50 million spores. This makes a striking 

 comparison when we consider the spore production in the Bryo- 



FIG. 223. Section of a leaf of Woodwardia, showing two sori: i, indusium; 

 sp, sporangia arising from the epidermis and in various stages of develop- 

 ment. Note the epidermis, stoma, s, palisade and spongy chlorenchymal 

 and vascular bundles, as in higher plants. 



phyta, and it is evident that ample provision is made for the 

 maintenance of the race notwithstanding the postponement and 

 specialization in spore production. 



The sporangia vary considerably in structure in the various 



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; /, lip cells. 



genera. In the simplest forms, they consist of a uniform layer of 

 wall cells inclosing a mass of cells, the majority of which become 

 spore mother cells, producing four spores each. In other cases, 

 a few of the wall cells are thickened, forming a rudimentary 



