Yapp. — Two Malayan ‘ Myrmecophilous ' Ferns . 225 
an early period, its place being taken by the ant-galleries, 
which are thus of lysigenous origin. 
3. The gallery system consists in both cases of a main 
ventral gallery which runs longitudinally through the stem, 
giving off two lateral series of galleries to the branches, and 
two series of vertical ones leading to the swollen leaf-cushions. 
Soon after leaving the main gallery the vertical ones branch 
so as to form two longitudinal series of dorsal chambers. In 
P. sinuosum these are entirely internal to the vascular system, 
and each consists of two limbs, one of which (the continuation 
of the vertical gallery itself) ends blindly in the leaf-cushion, 
while the other passes backwards through the tissues of the 
stem. In P. carnosum each dorsal chamber (the greater part 
of which is external to the vascular system) consists of three 
limbs ; two of these finally end blindly in one leaf-cushion, 
whilst the third passes forwards and ends in the leaf-cushion 
next in front on the opposite side of the stem. Thus each 
leaf-cushion in P. carnosum contains three blind galleries 
(arranged transversely), those of P. sinuosum being only 
provided with a single one. 
4. Communication between the galleries and the external 
air is effected by means of short passages excavated by the 
ants themselves in the soft tissues of the younger parts of the 
stem, 
5. The character and topographical position of the large- 
celled tissue seem to indicate that it was developed in the 
first instance as a special water-reservoir ; but the fact that it 
is so soon disintegrated may perhaps point to some degree of 
change of function, i. e. that the galleries which replace it 
have some important function to fulfil. There is no evidence 
that the galleries are an adaptation on behalf of the ants, and 
indeed their meaning is still somewhat obscure. Perhaps 
they serve as organs for the aeration of the stem, which is in 
both cases almost devoid of intercellular spaces. It is also 
possible that they assist to a slight extent in the absorption 
of water. 
6. The sori of P. carnosum are borne on marginal lobes. 
