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; fb, 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 1 
FIG. 115. Cyrtomium 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. 
