512 Bower.—Studies in the Phytogeny of the Filicales. 
pleuria , though it may happen repeatedly in near juxtaposition, as is seen 
in the case represented in Text-fig. 12. But it provides the explanation of 
that state of the fertile leaves of Platycerium , which, though described long 
ago by Hofmeister, and by Mettenius, has not yet been brought into line 
with other observations in Ferns. Mettenius, in his Filices Horti Lipsiensis 
(p. 26, PL IV, Figs. 1-3), described the double vascular system which occurs 
in Platy cerium. He showed how in the fertile region of this Fern fine 
branches spring from the vascular network of the normal leaf; these 
anastomose to a superficial network immediately within the lower surface: 
its meshes are elongated, and always much narrower than those of the sterile 
region, and only seldom give off free twigs. It is only this superficial 
network which bears the sporangia. Hof¬ 
meister, in his Higher Cryptogamia (Engl, 
edn., p. 252), described a similar condition 
in the circular or reniform nest-leaves of 
P. alcicorne. ‘ Their vascular bundles lie, not 
in one, but in two planes parallel to the surface 
of the frond. These bundles form two many- 
meshed nets, one close under the upper side, 
the other immediately above the lower side 
of the frond ; the two networks are united in 
many places by frequent ramifications, which 
pass through the mass of the frond in a trans¬ 
verse direction. 5 In my Studies on Spore- 
producing Members, No. IV (Phil. Trans., 
Series B, vol. 192, p. 86) the main results of 
these observers are confirmed as regards the 
fertile leaves, by examination of those of 
P. alcicorne , Desv. The double vascular 
system was thus known to exist in the leaves, 
and especially in the fertile areas of Platycerium. Also that the soral areas 
were not indiscriminately spread over the leaf-surface, but restricted to 
more or less parallel lines. This comes out most clearly in those cases 
where the fertile area is less prolific, and the leaf has the appearance of 
being only half fertile. Occasionally in these the sori appear quite isolated, 
and relatively short. It is such leaves as these which give a ready basis 
for comparison with what has just been described for Cheiropleuria. 
A semi-fertile area of Platycerium aethiopicum of this character is 
shown in Text-fig. 13. The venation is of the Dipteris-ty^e, as it is in 
Platycerium generally. The free twigs of the venation are elongated, 
though more greatly than they are usually in Cheiropleuria , and they bore 
downwards so that their distal ends approach the lower surface of the leaf. 
Often each is restricted to its own areola; but in not a few cases, on arriving 
Text-fig. 12. Part of lamina 
of Cheiropleuria with two large 
veins, showing the relation of the 
smaller veins to the patches of re- 
ceptacular storage-xylem. x, x, are 
points where the receptacular storage- 
xylem, in a lower plane, has crossed 
the limits of an areola of the vena¬ 
tion which lies in a higher plane, 
x 6 . 
