59 
be out of danger of liquid water, the end of the segment projecting 
slightly farther than that of the indusium, and often being toothed — 
with one tooth in L. Merrill i, with three in L. capillacea. Yapp suggests 
that the peculiarly placed sori of Lecanopteris will let the spores, escape 
only when there is wind enough to be likely to scatter them into such 
places as the plant normally occupies, which are in the 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 dryness of the fertile region. 
There are all grades of specialization in this respect, from that in which 
the preference of the sori for the distal end is doubtful, or, not empha- 
sized, as is the case in many species of Nepbrodium , Polypodium, etc., 
through those in which the restriction is clear and constant, as in 
Asplenium musaefolium , and those in which the fertile region is 
moderately restricted in its development in area, as Niphobolus adnascens , 
N. varius. Polypodium acceden-s, and P. angustatum, or otherwise modified 
in form, as in some species of Nephrol epis, or in structure, as in Ony- 
chium and Achrostichum, to those with the most completely metamor- 
phosed fertile region, as Dryostachum, Photinopteris, and Hymenolepis. 
In these extreme cases, 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 
longer. Among the ferns the dimorphism of which does not involve a great 
reduction of the assimilating area are Nephrodium diversilobum, Syn- 
gramma, Pteris ensifolia, P. pluricaudata, Taenitis, Niphobolus adnascens, 
N. Lingua, Polypodium palmatum and P. sinuosum. All , of these have the 
fertile fronds with the longer stipes. In Pteris there is a difference in 
the margin, and in P. ensifolia the fertile frond is. less compound than 
the sterile. The fertile fronds of Polypodium sinuosum yield to drought 
and fall off before the sterile. Other ferns with a moderate reduction 
of the assimilating area of the fertile frond are Hurnata heterophylla, 
H. parvula, Loxogramme conferta, Niphobolus nummularicefolius. Poly- 
podium incurvatum and Drynaria rigidula. These also either have longer 
stipes of the fertile 'frond or else, as in N . nummularicefolius 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 Humata parvula is 
5 to 8 centimeters high, that of the sterile frond 1 to 1.5 centimeters. 
Drynaria rigidula has the pinnse of the fertile frond more serrate than 
