Yapp , — Two Malayan * Myrmecophilous' Ferns . 213 
being found 1 within the limits of Blume’s genus Lecanop ter is 2 . 
The meaning of the flexion is not at first sight obvious. The 
only explanation that suggests itself to me is that it may 
possibly be connected with spore distribution. As we have 
seen, P. carnosum grows on mountains, as an epiphyte on 
the upper branches of trees. Often these trees are tall 3 , and 
it is only when the jungle is dwarfed on the highest mountain 
tops that it approaches at all near to the ground. Now the 
reflexing of the sori causes most at least of the little sorus-cups 
to face skywards instead of towards the ground (vide Fig. 1). 
The effect that this position of the sori would have on the 
ejection of the spores would probably be to cause most of 
them to be ejected from the sorus only when a considerable 
wind was blowing. Thus, if the sporangia had previously 
dehisced, a large proportion of the spores would still remain 
inside the sorus-cup or even on the concave upper surface 
of the leaf-segment, until the force of the wind were sufficient 
to shake the frond and carry them away. Under these con-* 
ditions, the spores would have a much better chance of 
reaching their destination, i. e. the topmost branches of trees, 
than if they fell to the ground first, as would often happen 
on still days, if the sori occupied the position usual in 
Ferns 4 . 
P. sinuosum , being a low-growing epiphyte, would have 
much less need of an adaptation of this sort. 
The reflexed sori, in their new position, would of course 
be more exposed to the effects of the heavy tropical rains 
than before. This, however, in all probability would not be 
a very serious drawback, as their most vulnerable part, i. e. 
the long thin stalks of the sporangia, would be safely hidden 
1 In a few Ferns sori may be actually borne upon the upper surface of the frond ; 
e. g. Deparia Moorei , Hook., whose sori are usually marginal, frequently bears 
additional sori scattered over the upper surface of the leaf. 
2 This genus is characterized by having the sori borne on marginal lobes, which 
are either bent back upon the upper surface of the leaf, or twisted to one side. 
3 Mr. Ridley informs me that on Bukit Timah, in Singapore, Polypodium car - 
nosum never grows at less than eighty feet from the ground. 
4 Mr. F. Darwin has suggested to me that this may be compared with the 
‘ Censer ’ mechanism found in the fruits of the Poppy and other flowering plants. 
