ba ) / n 
es siectitl Morphology and Classification. 3 3 13. 
‘ish in Polystichum, \near in Asplenium. They are occa- 
sionally naked, as in Polypodium (Fig. 439 v.); but more 
I. | Iv. 
Fic. 439. — Pinne of fronds of Ferns with sori; I. Asfrdium, the sporangia 
visible at the margin of the peltate indusium; II. Asplenium: III. Pteris 
aguilina; 1V. the same with the indusium thrown back to show the mode of 
attachment of the sporangia; WV. Polypodium, indusium wanting ; VI. Hymzeno- 
- phyllum or filmy fern; VII. the same ; the indusium partly removed to show the 
sporangia (all magnified). 
often covered by a membranous skin, the zvduszum [which 
is usually an extension of the epidermis] (Fig. 439 1.). In 
