Bower.—Studies in the Phytogeny of the Filicales. 511 
with two lines of areolae, and partially a third one, on either side of the 
midrib. Smaller twigs of vascular tissue extend into the areolae. Text- 
fig. 1 shows this, and the relation to it of the sori which remain on the one 
side of the drawing, but have been removed on the other. Each sorus is 
seated near to the centre of its areola, upon a vein connected with its 
margin. The vascular tissue does not show any characteristic extension 
into the receptacle, which in its position and in its vascular relations is 
similar to that in Matonia. 
Much the same is the case with Dipteris conjugata , which is the 
broadly webbed species (compare Land Flora, Fig. 346). Through 
D. quinquefurcata , as explained elsewhere (Land Flora, p. 618), the transi¬ 
tion is seen from the simple arrangement of sori on a narrow leaf to the 
webbed condition with very numerous sori scattered over its enlarged 
surface. But in D. conjugata the relation of the sori to the venation 
remains the same (Text-fig. 2); each is seated at the centre of its areola, 
above a branched vein which is connected with the boundary of its own 
areola. Thus whatever may be the differences of the sporangia in size, 
number, construction, or development, the relation of the sori to the 
venation is substantially uniform, so far as observation goes, in the genus 
Dipteris. 
But when we pass to Cheiropleuria , while the relation to the venation 
is still essentially as in Dipteris , it will be seen that an extension occurs 
which is important in facilitating a comparison further with Platycerium . 
The fertile leaf differs from the sterile in being long and narrow, and 
upright in position. Its venation is the same as that of the sterile leaf in 
essentials, but upon a contracted plan ; so that the areolae are much less 
numerous. If an examination be made of the thinner area of the fertile 
leaf, right and left of the midrib, which the soral area seems to cover entirely, 
and the venation be traced, it will appear as in Text-fig. 12. Clearly 
the method of venation is as in the fertile leaf of Dipteris , as would indeed 
have been expected from its similarity in the sterile leaves, old and young. 
But the important difference appears, that whereas in Dipteris the terminal 
twigs do not appear distended as wider storage tracheides, this is a marked 
feature in Cheiropleuria. Here the endings form considerable tracts of 
xylem, composed of tracheides with a high proportion of breadth to length, 
and these tracts may themselves be considerably elongated, while they 
extend so markedly towards the lower surface of the leaf, on which the 
sporangia and paraphyses are seated, that the distal tracheides lie very 
closely below the sporangial stalks. Further, it may occasionally be seen 
(as at ‘x’ in Text-fig. 12) that these receptacular extensions are not limited 
to a single areola, but pass in a lower plane than the limiting vein into the 
next areola, actually crossing the course of the vein limiting the areola, but 
in a lower plane. This is not a very marked or frequent feature in Cheiro - 
