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; li, lip-cells; 
an, annulus; si, stalk; s^>, 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. 1 1 8. 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. u 8. Types of fern sporangia. A, Loxsoma Cunninghami; B, 
Gleichenia circinata; C, Todea barbara; D, Thyrsopleris 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- 
