484 Boodle.—Anatomy of the Hymenophy l laceae. 
All the Hymenophyllaceae being filmy, there are no stomata 
in the lamina, and further, as far as is known, stomata do not 
occur in any part of the plant l . It is most convenient to apply 
the word ‘ filmy ’ to leaves which possess no intercellular 
spaces, rather than to reserve it for leaves whose lamina is 
strictly one cell thick. In the above sense T. reniforme is 
filmy, though the lamina is four cells thick. The absence of 
intercellular spaces gives to a leaf a translucent appearance, and 
from the external appearance it is hardly possible to distinguish 
a leaf that is one cell thick from one that is two cells thick. 
As the Hymenophyllaceae have probably been derived from 
Ferns that were not filmy, it was possible that abortive stomata 
might be found, but a search for them gave negative results. 
The cells (a and b ) shown in Fig. 43 bear a certain resemblance 
to the guard-cells of a rudimentary stoma, but this is probably 
accidental. It was the only case of the kind met with, and 
occurred in an early leaf of a plant of T. Bancroftii. Some 
cases of filmy Ferns outside the Hymenophyllaceae, namely 
Todea superb a, Col., T. hymenophy lloides, Rich, and Less., &c., 
and Asplenium resectum , Sm. 2 , were examined for compari¬ 
son. All their leaves appeared to be destitute of stomata. 
Subsequently, however, some very young ‘ seedlings 5 of T. 
hymenophy lloides, with the first two leaves only, were found 
connected with their prothalli. Prothalli, mostly without 
young sporophytes, were resting on the upper side of the 
leaves of a plant of this species, which had abundant mature 
sori on the lower side of its leaves. The conditions were such 
as to make it practically certain that the prothalli belonged 
to the plant on which they were found. Some prothalli had 
been formed by the germination of spores in their sporangia, 
which were ruptured but still arranged in sori on the lower 
side of the leaf. This occurred where part of a leaf had 
become turned upside down. Then again, where one leaf 
rather closely overhung another, sporangia and spores had 
fallen on to the surface of the lower leaf, and it was leaves 
1 Prantl, 1 . c., p. 23. 
2 See Bower, Annals of Botany, III, p. 348. 
