286 



PRACTICAL BOTANY 



FIG. 238. The bulblet fern (Cystopteris bulbifera) 



A, a leaf upon which vegetative reproductive growths 



or bulbs (6) are formed ; B, a section of the leaf on 



the underside of which groups of sporangia (indusia) 



are borne ; C, one indusium in detail 



spores are produced, a com- 

 paratively small part of the 

 sporophyte is given to spore 

 formation, most of it doing 

 nutritive work. The fern 

 sporophyte may grow from 

 year to year (is perennial), 

 producing new leaves, a new 

 supply of food, and new crops 

 of spores each year. 



The complexity and prom- 

 inence of the fern sporo- 

 phyte and the comparative 

 simplicity and inconspicu- 

 ousness of the gametophyte 

 are forerunners of the greater 

 increase in sporophyte and 

 decrease in gametophyte 

 that is to be found later in 

 higher plants. 



265. Types of ferns. 

 Ferns are usually 

 distinguished from 

 one another by the 

 leaves, the sori, and 

 the sporangia. There 

 is considerable varia- 

 tion in position and 

 arrangement of sori 

 in different ferns 

 (Figs. 232,238,239), 

 In some the sori are 

 regularly placed dots 

 upon the leaf. In 

 others, as the maiden- 

 hair fern (Adiantum) 



