LIFE HISTORY OF A FERN 



155 



cluster of tiny stalked cases. The cases contain minute 

 •unicellular reproductive bodies called spores, and the en- 



FiG, 114. — Cross-section through the marginal sorus of a sporophyll of 

 the bracken fern (Pteris aquilina). I, palisade layer; /&, vascular bundle; 

 sp, sporangium; in, indusium. (Greatly magnified.) 



tire structure is a sporangium. The place where the 

 sporangia are attached to the leaf is the sporangiophore^ 



Fig. 115. — Cyrtomiiim falcatum. Under (dorsal) surface of a portion of 

 a sporophyll, showing the numerous sori on the pinnae. 



(Fig. 114), and over all is often found a thin membranous 

 covering, the indusium (Figs. 114 and 115). In some ferns 

 the indusium is lacking, and the sorus is naked. Spore- 



1 Also called receptacle. 



