156 



STRUCTURE AND LIFE HISTORIES 



bearing leaves are called sporophylls, and plants that bear 

 sporophylls are called sporophytes. 



144. Types of Foliage-leaf. — In some ferns the foliage- 

 leaf presents a simple, unbranched blade, and petiole; 

 but in other species the blade is variously branched. In 

 such cases the larger, primary divisions are called pinn(Bj 



Fig. 1 1 6. — Fern leaves, showing various degrees of subdivision or branch- 

 ing of the blade. A, Phyllitis; B, Polypodium; C, Pteris; D, Adiantnm. 



and the secondary subdivisions pinnules. Illustrations 

 of these various types are shown in Fig. ii6. 



145. Sporangia. — As noted above each sporangium con- 

 sists of a spore-case borne on a stalk (Fig. 117). The struc- 

 ture of the case varies considerably in various groups of 

 ferns, but it usually possesses walls only one cell thick, with 



