60 
those of the sterile and much more readily decidnons. Ilumata hetero- 
phylla has the sterile frond entire, bnt the fertile one toothed or lohed. 
The significance of these differences 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, the 
stomata are, area for area, more numerous on the fertile frond than on 
the sterile, as the following table illustrates, the numbers being the 
stomata per square millimeter. 
Sterile. Fertile. 
Xephrodium diversilobum 
140 
200 
Aspidium angulatum 
36 
180 
Loxogramme conferta 
8 
28 
Xiphobolus nummular icrfolivs 
64 
100 
Polypodium accedens 
23 
52 1 
The stomata of the fertile and those of the sterile frond of Clieiropleuria 
differ in the series of divisions by which they are formed, the latter being 
unlike those which I have found in any other fern (figs. 26, 27.) 
There still remain a few ferns in which the differentiation has gone 
so far that the assimilating, but not spore-hearing, surface of the fertile 
frond has practically been obliterated. These are Leptochilus and Cheiro- 
pleuria , still with some expansion of green lamina, the nether surface 
of which is completely covered, at least at maturity, with sporangia ; 
Bleclmum egregium, the fertile pinnae of which are expanded at the 
base only; and Psomiocarpa, Stenosemia , Stenochlcena, and Lomagramma, 
whose fertile fronds are almost completely without assimilating surface. 
Of these, Btenoclilcena and Lomagramma are seandent, all the others 
except Blechnum egregium having the stipes of the fertile fronds notably 
long. The two seandent genera have the pinnas articulate to the rachis, 
and the pinnae 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 both 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 species), Psomiocarpa and Stenosemia are terrestrial 
plants characteristic of the border between high forest and savanna-wood. 
Their close neighbors are N ephr odium diversilobum and Aspidium angu- 
latum. To endure the dryness of the dry months, these plants have 
their fronds close to the ground; such species as Psomiocarpa apiifolia, 
Leptochilus latifolius, and their Luzon associate, Hemionitis arifolia ; 29 
are often real rosette-formers. If their spores were matured at this time, 
» Fertile apical region. 
29 Whitford, 1. c., 399. “All but geopliilous during the di'y season.” 
