LIFE HISTORY OF A FERN 



157 



a clearly differentiated region, the annulus, composed of 

 cells whose radial and inner cell-walls are greatly thick- 

 ened. Various types of spore-cases are illustrated in 



Fig. 117. — Sporangia of an undetermined species of fern; U, lip-eelis; 

 an, annulus; st, stalk; sp, mature spores. Each of the four nuclei in the 

 upper cells of the stalk is in the terminal cell of one of the four rows of cells 

 that compose the stalk. 



Fig. 118. Among the group of ferns which are now most 

 common, and to which the bracken fern (or "brake"), 

 the maiden-hair fern, the common polypody, and others 



Fig. 118. — Types of fern sporangia. A, Loxsoma Cunninghami; B, 

 Gleichenia circinata; C, Todea Barbara; D, Thyrsopteris elegans; E, Matonia 

 pectinata; F, Lygodium japonicum. (Redrawn from various sources.) 



belong, the sporangium always originates from a single 

 epidermal cell. Ferns whose sporangia thus originate are 

 called leptosporangiate ferns. The walls of their spore- 



