58 
These hairs on the ends of all mature sporangia make the whole sorus 
incapable of being wet. 
Spores of ferns are in general not readily wet, because of their waxy 
and often rough or reticulate surfaces. They are rough, for instance, 
in N ephrodium. procurrens , N. 1611, N. Bordenii, Aspidium angulalum 
and Asplenium resectum; granular in N. setigerum, and reticulate in 
1ST. 1685. Their resistenee to wetting not merely facilitates their dis- 
persal, but also insures them against germination under too temporarily 
favorable conditions. 
The immersed sori of Prosaptici contigua and several species of Poly- 
podium are very effectively protected against any danger of wetting by a 
few long brown hairs standing across the mouth of the pit. 
Very numerous ferns provide, in a variety of ways, that the dryness 
necessary for the dispersal of the- spores shall involve the least possible 
danger of desiccation of the vegetative frond. One very simple means to 
this end is the location of the sori on the margin, or even on teeth. 
The marginal or apical position of the sori has been assumed inde- 
pendently by the plants in many different groups of ferns. Mindanao 
illustrations are the Hymenophyllacece, Dicksoniece, Psomiocarpa , etc. (in 
bionomic effect), Nephrolepis acutifolia, many Davallice and ILumatce, 
D ennstaedtia, Odontosoria, Lindsaya, the Pteridece, Prosaptia, Acrosorus, 
Lecanopteris , and Lomagramma. As the primary purpose of this posi- 
tion of the sori is to insure the dryness of the sporangia and spores, it is 
characteristic of plants growing in the most moisture-laden atmosphere; 
as in the rain and mossy forest where the Hymenophyllacece, Dicksonia, 
Dennstaedtia , Lindsaya and Lomagramma are examples, or along creeks, 
in the case Odontosoria-, they also occur on some vigorous xerophytes such 
as Davallia, Humata, N ephrolepis acutifolia , and Lecanopteris. The 
relation between the atmospheric moisture-conditions and the position 
of the sori is well illustrated by ferns other than those with sori actually 
on the margin. Diplazium meyenianum is much more constantly re- 
stricted to moist hollows than is its occasional companion, D. polypod- 
ioides, the former having flat segments, with long sori' reaching the 
margin, while the latter has short, costal sori, protected against liquid 
water by the concavity of their surface of the segment. Asplenium Phyl- 
litidis of the rain-forest has long sori reaching nearly or quite to the 
margin, while A. musaefolium of the high forest and strand has them 
short and costal. It is common in N ephrodium § Goniopteris, and the 
Lastrcea species of similar form, for the sori to be more nearly costal 
at the ends of the segments than at the base; N. 1685 is a good example. 
The tooth position is obviously drier than the merely marginal. The 
Lindsay ce growing in the moistest places are deeply cut— even finely 
dissected in L. blumeana, and in L. capillacea Christ, of the mossy forest 
of Luzon. As a rule, these sori lack just enough of being marginal to 
