f 
60 
tho^e of the sterile and mnch more readily deciduous. Ilumata lictcro- 
phjUa has the sterile frond entire, but the fertile one toothed or lobed. 
The significance of these diiTercncos in maintaining the dryness of the 
fruiting surface has been made clear by a preceding discussion of the 
value of such margins. 
As a general rule, among these moderately dimorphous ferns, tlie 
stomata are, area for area, more numerous on the fertile frond than on 
the sterile, as the f(^llo^Ying table illustrates, the numbers being the 
stomata per square millimeter. 
sterile. Fertile. 
'NepJiiodiuiii dircrsiJohum 140 200 
Aspidium''anyiilat um 36 ISO 
Loccogramme conferta 8 "° 
Xipliohohis numlnulariafoVius A 64 100 
Paly podium accedens - 23 52^ 
The stomata of the fertile and those of the sterile frond of Chciropleuria 
differ in the series of divisions by wliich they are formed, the latter being 
imlike those which I have foimd in any other fern (figs. 26, 27.) 
There still remain a few ferns in which the differentiation has gone 
so far that the assimilatijig, but not spore-bearing, surface of the fertile 
frond has practically been obliterated. These arc LeptocJiilus and Cheiro- 
pleuria, still with some expansion of green lamina, the nether surface 
of which is completely covered, at least at maturity, with sporangia; 
Blechnum egregium, the fertile pinnae of which are expanded at the 
base only; and Psomiocarpa, Stenosemla, Stenoclihena, and Lomagramma, 
whose fertile fronds are almost completely without assimilating surface. 
Of these, Stefiochlcena and Lomagramma are scandent, all the others 
except Dlecknum egregium. haying the stipes of the fertile fronds notably 
r 
long. The two scandent geiiera have the pinnae articulate to the ruchis, 
and the pinme of the fertile fronds of both are much more caducous than 
those of the sterile. This, with the further fact that only plants of a very 
considerable age are fertile, makes fertile fronds of botli hard to find. 
The fructification of Lomagramma originates on the nether surface but 
becomes lateral, as exposed as possible, by the curling of the frond 
(fig. 28). 
The fertile frond of Blechnum egregium as well, seems to be both rare 
and transitory, and on all these ferns they are to be found only in season. 
Leptochilus (most a^Gcics) ^ Psomiocarpa and Sienosemia are terrestrial 
plants characteristic of tlie border between high forest and savanna-wood. 
Their close neighbors are Nephrodium diversilohum and Aspidmm angu- 
latum. To endure the dryness of the dry months, these plants have 
their fronds close to the ground; such species as Psomiocarpa apiifolm, 
Leptochilus laiifolins, and their Luzon associate, IlemionUis arifoUa,'''' 
are often real rosette-formers. If their spores were matured at tliis time, 
« Fertile apical region. 
^'^Wliitfonl, 1. e., .309. "All but gcupUilous during the dry season." 
