xcrophytic genera, DavaUia ami llumaia. but not in their mtv^ophytic 
relatives, Microhpia aiul Leucodegia, aiul iu A. •< pi en in in it is the xcro- 
phytic section, with entire fronds, which has hy far the firmest in<hisia. 
A heavy coating of liairs protects the soii as well as tlic stoinata agamst 
undue loss of water in Xiphobohis Vuigaa 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 whicli 
cover the sporangia so thoroughly that they must serve in their time in 
both ways. Among these are AclirostuJium, Lomagramma, Cheiro- 
pleuria, various Y{Uar\e(p, Ilijmenolepis, and Pohjpodinm enhauncu- 
latum; and, most conspicnonsly of all Philippine ferns, Pohjpodiam 
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 Pteridecp. The same 
effect, is reached very thoroughly by two of our species of Poly podium 
P. cncullaiuin and P. gra^illirmim — which liave one half of each piana 
wholly or partly folded backward against the other half, covering the 
single sorus. This, or a convexity approaching the same effect, .charac- 
terizes VvQsVs'gOTiiiA-Cahjmmodon. in Acrosorm, the folding is complete 
J 
and permanentj the edge being grown fast and the sorus opening toward 
r 
the apex. 
■ Xumerons ferns prot(xt 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, tlie spots occupied 
by tlie sori may or may not be prominent on the upper surface of the 
frond. When they make moderately convex spots it strengthens the 
frond Tuechanically, so that the fertile part of the frond of Nephrodium 
Foxii, for instance, retains its form for some time after the sterile part 
begins to wilt. Ferns with indusiate sori moderately immersed arc 
Did y mod il ana, Xephrodium Foxii, N. imrnersum, M'lcrolepia hlrsula, 
Hnmata imviersa, and DavalHa pallida. In Aspleuium Phyllitidis (fig. 
19) and its immediate relatives, they are snnken approximately half 
the depth of the frond, opening obliquely, and the part of the frond 
outside them merging into the indusium. In Scolopendiiuni pinnaium 
{^g. 20) the double sori are immersed, the entire broad depression being 
covered by the indnsia. Non-indusiate sori shallowly immersed arc 
found in some species of Antrophyum, Loxogramme conferta, 2'aenitis, 
Polypodinm prdiculatum, P, Phymaiodes, P. palmaium., P. anguaiaimn, 
P. mnuosnm-, P. heradeum, Drynaria rigidula and Lecanopferis. Poly- 
podium revolutum and P. ccEspitosnm have them deeply immersed in 
fleshy fronds. This goes farther in P. celehicum, and reaches an extreme 
in the less fleshy fronds of P. ohJiquaium (fig. 21), which has the cavity 
deepened hy a crater-like rim. In this species and its immetliate relatives 
(Crypiosorm Fee) the cavitv is closed when the sorus is very vonno-, bnt 
opens later. In Prosaptla, the cover has become permanent, and tlie 
