INTRODUCTION. 49 
2. Allosorus.—Sori round or sub-oblong, becoming laterally con- 
fluent, hidden beneath the scarcely attenuated reflexed 
margins of the frond. 
$ il.—GYMNOGRAMMER.—Sori linear, parallel with the veins, naked, i.e. 
without indusia, dorsal on the veins. 
3. Gymnogramma.—Sori linear, forked below; (an annual or 
biennial Fern). 
*,* CETERACH which has linear sori, also has the indusium obsolete, 
so as to simulate naked linear masses. See this genus 
under $ iv. ASPLENIER. 
$ iii. —AsPrprEm.—.Sori punctiform, rotundate, covered while young by scale-like 
indusia of the same form, dorsal on the veins. 
4, Polystichum.—Sori covered by circular peltate indusia, attached 
at their centre. 
5. Lastrea.—Sori covered by reniform indusia, attached at the 
notch on their indented posterior side. 
§ iv.—AsPLENIEA.—Sori oblong or linear, covered while young by scale-like 
indusia of the same form, lateral on the veins. 
6. Athyrium.—Sori oblong, lunately curved, sometimes (espe- 
cially the basal ones) hippocrepiform or horse-shoe-shaped, 
the indusia attached along their concave edge, the free 
margin fringed ; venules free. 
7. Asplenium.—Sori simple, linear or oblong, oblique; venules 
free. 
8. Scolopendrium.—Sori double, i.e. in proximate oblique parallel 
pairs face to face, covered by elongate straight indusia, 
which open along the centre of the double or twin sorus ; 
venules free. 
9. Ceterach.—Sori simple, oblong, scattered, growing from the 
anterior side of the veins (except the lowest on each pinna 
which is on the posterior side), hidden among imbricated 
chaffy scales ; indusium obsolete ; venules reticulated. 
E 

