8 Bower. — Studies in the Phytogeny of the Filicales. VI. 
But the special interest attaches to the fertile blade. Here the soral areas 
occupy the whole lower surface between the midrib and the slightly enlarged 
margin, as shown in Text-fig. 2, xvii. The rather fleshy expanse is 
traversed towards its upper surface by a reticulum of stronger strands, 
corresponding to that of the sterile lamina. But in addition to this there is 
a second system connected with it, which ramifies in a plane below, but 
parallel to it, spreading immediately below the soral surface. The appear- 
ance as seen in transverse section is suggested by Text-fig. 2 , xvii, which 
further indicates that the sub-soral system consists of very minute strands. 
The relation of these two systems is indicated in Text-fig. 3, which repre- 
sents part of a fertile lamina made transparent, and stained so as to bring 
into prominence both series. The main reticulum of the lamina is repre- 
sented by heavy lines ; this indicates the coarser texture of its strands, 
Text-fig. 3. Portion of the soral region of the sporophyll of Leptochilus tricuspis. ' The heavier 
and continuous lines represent the normal venation of the leaf, which is nearer the upper surface. The 
lighter and broken lines represent the receptacular system extended in a plane nearer the lower 
surface, x 5. 
which are connected directly with the midrib. The sub-soral system arises 
from the main reticulum, and is connected with it at many points by strands 
which run obliquely downwards from it to the sub-soral level. Sometimes 
such a strand develops only a few ramifications, and the whole falls within 
a single areola of the main reticulum. But more frequently the branching 
is more elaborate, and the resulting system, fusing with like strands originat- 
ing elsewhere, constitutes the connected sub-soral network. Frequently 
strands of this network cross those of the main network, but at a lower 
level and without actual junction at the point of crossing ; and this is seen 
with special frequency towards the margin. 
The structure thus described, which may be designated as diplodesmic , 
corresponds to what has been seen in Platycerium , and in less degree in 
Cheiropleuria . In the latter it has been shown 1 that while the vascular 
supply to the sorus is the same in principle as that in Dipteris , 2 it is not 
limited to each areola of the main venation, but is liable to extend in a lower 
1 Ann. ofBot., 1915, p. 512, Text-fig. 12. 
2 1 . c., p. 499, Text-fig. 2. 
