The Philippine journal of science. [Vol. 67, no. 1]

8

The Philippine Journal of Science

1938

and Vandenboschia. The tube is more than one layer of cells
thick in Trichomanes s. str. but not in all groups of Trichomanes
s. lat.; this difference merits detailed study.
The receptacle is typically included-that is, not longer than
the involucre-in "Hymenophyllum;" of indefinite length, by
basal intercalary growth, in Trichomanes. In Trichomanes s.
lat. there is uniformity of type, the globose tip and the inflated
base on which respectively Presl based his genera Cephalomanes
and Ragatelus being illusory. The receptacle of Meringium and
its derivatives and of Leptocionium is like that of Trichomanes,
indefinitely long. That of Hymenophyllum s. str. is of the same
type but of limited growth, not typically exceeding the involucre.
In Mecodium and Sphaerocionium, growth ceases by the time
the sporangia develop, the latter being simultaneous.-Simplices,
of Bower. In each of these genera there are natural groups
of species with cylindrical receptacles, and others with more or
less globose receptacles, all having longer or shorter sterile bases.
These are illustrated for very many Mecodium species in my
Hymenophyllum.13 I place in Mecodium some American species
with extruded receptacle. The sporangia may be sessile on the
body of the receptacle, or may be borne on more or less prominent outgrowths, sporangiophores. Some species produce basal
paraphyses.
The sporangia are uniform in type, sessile, with an obliquely
transverse annulus interrupted by the stomium. In general they
are large, with many superficial cells and up to 256 or 512 potential spores in Hymenophyllum s. lat.; small, with few superficial cells and comparatively few spores, in Trichomanes s. lat.
Bower has studied these most amply, and concludes that species
producing very numerous sporangia produce correspondingly
small ones. However, Cardiomanes bears very long receptacles
with indefinitely many sporangia as large as are known in any
leptosporangiate fern.
In the range of modifications in vegetative form and structure in adaptation to a generally humid environment, the Hymenophyllaceae exceed any other family in the plant kingdom.
This statement may astound those accustomed to the summary
dictum that these are plants of very simple structure, but I make
it with confidence. In a humid environment transpiration is
limited. The leaf structure, evolved in perfect adaptation to
the environment, then demands that the transpiration be lim

Philip. Journ. Sci. 64 (1937) 1.