VI. POLTPODIACEAE. 123 



Keys to the tribes and genera. 



1. Indusium present, free from the margin or consisting of the reflexed or 



recurved, modified margin or portions of the margin. 



3. Indusium cupuliform, globose or sausage-shaped, fastened beneath the 



sorus on all. sides, but apparently so in genus N°- 13, open at the 



top or bursting down irregularly. § 1. W^opdsieae. 



3.S. Indusium oblong, round or i-eniform, fastened above the sorus, attached 



by a longitudinal axis, a central point or at the top of a + deep 



sinus, opening all round the edge or nearly so. § 2. Aspidieae. 



3.3.S. Indusium roundish, oblong or linear, fastened mostly at 1 side of the 



sorus, opening at the opposite, free edge. 



3. Indusium marginal, consisting of the reflexed or recurved margin 

 or portions of the margin, opening inwardly. § 4. Pterideae. 

 3.3. Indusium not marginal, but often reaching the margin with 

 one of the free edges. 



A. Sori either roundish and solitary (dorsal or terminal) on the 

 veins, or oblong to linear and uniting the apices of 2 or 

 more veins. Indusium attached at least at the inner side of 

 the sorus, opening outwardly. § 3. Davallieae. 



S:.A. Sori linear or oblong, strictly parallel to the central ribs 

 of the ultimate segments. Indusium attached at the outer 

 side of the sorus, opening inwardly. § 5. Olechneae. 

 A.A.A. Sori linear or oblong, ', single or double, straight to 

 horseshoe-shaped, springing from the sides of the veins, 

 rarely placed between the veins, oblique to the costa, some- 

 times subparallel to the latter or occupying the single 

 central vein of narrow, ultimate segments. Indusia springing 

 from the same side as the sori, mostly opening obliquely 

 towards the costa. § 6. Asplenieae. 



±.±. Indusium wanting. Sori sometimes covered by the recurved, not modified 

 margin or portions of the margin, often more or less deeply sunk in 

 marginal or dorsal grooves or pit-like, saccate or indusium-shaped cavities 

 or depressions of the frond. , 



«. Sori indefinite, the sporangia crowded over the under surface or 

 portions of the under surface, not rarely becoming narrowly linear 

 or sometimes extending on both surfaces in the plants with much 

 contracted fertile fronds or segments. § 11. Acrosticheae. 



