xerophytic genera, Davallia and TLumata, but not in their mesophytic 
relatives, Microlepia and Leucostegia, and in Asplenium it is the xero- 
phytic section, with entire fronds, which has by far the firmest indusia. 
A heavy coating of hairs protects the sori as well as the stomata against 
undue loss of water in N iphobolus lingua and various of its congeners. 
While the function of paraphyses is in general to protect against water 
rather than desiccation, there are some ferns the paraphyses of which 
cover the sporangia so thoroughly that they must serve in their time in 
both ways. Among these are Aclirostichum, Lomagramma, Cheiro- 
pleuria, various Vittariece , Hymenolepis, and Polypodium subauricu- 
Jatum; and, most conspicuously of all Philippine ferns, Polypodium 
lineare Thunb., of Luzon. 
The protection of the sorus by the folding backward of the margin of 
the frond is familiar to all in the “indusia” of most Pteridece. The same 
effect is reached very thoroughly by two of our species of Polypodium — 
P. cucullatum and P. gracillimum — which have one half of each pinna 
wholly or partly folded backward against the other half, covering the 
single sorus. This, or a convexity approaching the same effect, charac- 
terizes Presl’s genus Calymmodon. In A crosorus, the folding is complete 
and permanent, the edge being grown fast and the sorus opening toward 
the apex. 
Numerous ferns protect their young sori by more or less completely 
sinking them below the level of the frond’s surface. According to the 
extent of the immersion and the thickness of the frond, the spots occupied 
by the sori may or may not be prominent on the upper surface of the 
frond. When they make moderately convex spots it strengthens the 
frond mechanically, so that the fertile part of the frond of N eplirodium 
Foxii, for instance, retains its form for some time after the sterile part 
begins ■ to wilt. Perns with indusiate sori moderately immersed are 
Didymoclilcena, N eplirodium Foxii , N. immersum, Microlepia hirsuta, 
Ilumata immersa, and Davallia pallida. In Asplenium Pliyllitidis (fig. 
19) and its immediate relatives, they are sunken approximately half 
the depth of the frond, opening obliquely, and the part of the frond 
outside them merging into the indusium. In Scolopendrium pinnatum 
(fig. 20) the double sori are immersed, the entire broad depression being 
covered by the indusia. Non-indusiate sori shallowly immersed are 
found in some species of Antropliyum, Loxogramme conferta, Taenitis, 
Polypodium pediculatum, P. Phymatodes, P. palmatum, P. angustalum, 
P. sinuosum, P. heracleum, Drynaria rigidula and Lecanopteris. Poly- 
podium revolutum and P. ccespitosum have them deeply immersed in 
fleshy fronds. This goes farther in P. celebicum, and reaches an extreme 
in the less fleshy fronds of P. obliquatum (fig. 21), which has the cavity 
deepened by a crater-like rim. In this species and its immediate relatives 
( Cryptosorus Fee) the cavity is closed when the sorus is very young, but 
opens later. In Prosaptia, the cover has become permanent, and the 
