#^ 
59 
be out of danger of liquid water, the end of the segment projecting 
sliglitly farther than that of tlie indusiuui, and often being tootlied — 
with one tooth in L. MerriU% with three in Jy. capiUarca. Yapp suggests 
that tlie peculiarly placed sori of Lecanopteris will let the spores esonpe 
only when there is wind enough to be likely to scatter them into such 
places as the plant normally occupies, wliich are in tlie crowns of lofty 
trees. 
It is probable that a considerable majority of all ferns have the fruct- 
ification developed toward the apex rather than toward the base of the 
frond, obviously favoring the greater dr^Tioss of the fertile region. 
There are all grades of specialization in this respect, from that in w bich 
the preference of the sori for the distal end is doubtful, or not empha- 
sized, as is the case in many species of Neplivodium, Poly podium, etc., 
through those in which the restriction is clear and constant, as in 
Asplenium musaefoUufn, and those in which the fertile region is 
moderately restricted in its development in area, as Nipliobohui adnaacetis, 
N. variuSj Polypodlum accedcns^ and F. angustatum, or otherwise modified 
in form, as in some species of Nephrolepis, or in structure, as in Ony- 
clilum and Aclirodlchum^ to those with the most completely juetamor- 
phosed fertile region, as Dryosiachuiu, Phoiiiioplcris, and Ilymenolep'is. 
In these extreme cascs^ the fern seems to gain the most of the advantages 
of dimorphism, with decided economy of material, and still more in 
the conduction of food to the fertile part. 
The adequate dryness of the mature reproductive structures, without 
jeopardy to the proper performance of the vegetative functions, is accom- 
plished in many ferns by a specialization of entire fronds for one or the 
other end. In many ferns there is little or no specialization other than 
a difference in the length of the stipes, those of the fertile frond being the 
lon^^er. Among the ferns the dimorphism of which does not involve a great 
reduction of the assimilating area are Xcphrodlum diversUulum, Syn- 
gramma, Pteris ensifolia, P. pluricaudafa, Taniitis, Niphoholus adna^cem, 
N, Lingua, Polypodlum palnuittim and P. sinno<ivm. All of these have the 
fertile fronds with the longer stipes. In Pieris there is a difference in 
the margin, and in P. ensifolia the fertile frond is less compound than 
the sterile. The fertile fronds of Polypodlum sinno.vnn yield to drought 
and fall off before the sterile. Other ferns with a moderate reduction 
of the assimilating area of the fertile frond are Ilumala hderophyUa, 
11. parvula, Loxogramme conferta, Xiphohohi.^ nummuJamrfoliw^, Poly- 
podium incurvaiwm and Drynaria rigidtda. These also either have longer 
stipes of the fertile frond or else, as in N, nummularu^f alius and L. 
conferta, the fertile frond is itself elongate, while the sterile frond is 
more or less round. The stipe of the fertile frond of llnmaia parvula is 
5 to 8 centimeters high, that of the sterile frond 1 to 1.5 centimeters. 
Drynaria rigidula has the pinnie of the fertile frond more serrate tlian 
