Bower.—Shtdies in the Phytogeny of the Filicales. 507 
Ferns in the axial stele. 1 Their occurrence in the Dipterid affinity has 
a special interest, in connexion with the comparisons with Platycerium 
to be instituted below. 
In the case of the fertile leaf of Cheiropleuria , the outline of which is 
simple and narrow, the fertile region has as a rule a marked midrib, while 
two thickened ridges mark the margins. The extensive soral area covers 
the more or less extensive tracts within these, right and left of the midrib. 
A transverse section of the fertile lamina then shows in outline as in 
Text-fig. 8, viii. The difference between this and the sterile lamina is 
more apparent than real, as is seen if the vascular system is followed from 
below upwards. The petiole of a sporophyll shows at a middle level 
a condition as in (iii), and (iv) of the sterile; but above that level, instead 
of the fused median strand dividing again, as in the sterile petiole, it con¬ 
tinues its fused course directly into the fertile lamina, where it forms the 
midrib (Text-fig. 8, vii, viii). A comparison of the result may be drawn 
between this condition of the fertile lamina and that of the leaf-segments 
in Dipteris quinquefurcata , or Lobbiana (Seward, 1 . c., Figs. 18, 24; or 
Land-Flora, Figs. 343-5). If we imagine the branched sporophyll of 
either of these species represented only by a single segment, it would have 
substantially the vascular structure of the fertile lamina of Cheiropleuria. 
The venation of the distal end of the sporophyll is worthy of note, as 
in some degree harmonizing the difference between that of the sterile and 
fertile leaves. The soral areas frequently stop short of the extreme tip, 
which may then extend for some distance as a narrow beak. It may be 
traversed by a midrib with lateral reticulate branchings; or it may show 
two marginal ribs, with reticulations between them. Or, again, various 
other irregularities may be seen, including loops of the main veins quite 
comparable with those often found in Dipteris. All these facts appear to 
harmonize with the idea of the leaf of Cheiropleuria being a webbed and 
simplified example of the fundamental type seen in Matonia and Dipteris. 
Platycerium. 
As it will be necessary later to draw comparisons between Cheiro¬ 
pleuria and Platycerium , genera which have already been placed in near 
relation to one another by various writers, it will be convenient to introduce 
here certain facts relating especially to the vascular system of the latter 
genus. The similarity of the venation of the young leaves of Platycerium 
to that of Cheiropleuria and Dipteris has already been noted. Putting 
aside the remarkable dimorphism of the leaves in the genus, which is 
related to its epiphytic habit, the outline of the fertile leaves of Platycerium 
is often very closely conformable to that seen in the genera named. As an 
1 Compare Tansley, The Filicinean Vascular System, p. 65. 
