24 Bower. — Studies in the Phylogeny of the Filicales. VI. 
gaps in the lower strap (p, p ) which are not related to leaf-traces, and appear 
to be of the nature of perforations. 
The additional complications thus seen in Z. cuspidatus bear a 
comparative interest.' The presence of occasional perforations, not constant 
in position or in number, gives an intermediate step between the more 
primitive non-perforated state, as seen in Metaxya or Dipteris , and the more 
regularly perforated, as in N eocheiroptems or L. tricuspis . The latter is the 
general condition in the advanced Polypodioid Ferns. It is interesting 
in this connexion to recall the occasional presence of a leaf-gap in Metaxya . , 
as shown in Ann. of Bot., vol. xxvii, PI. XXXII, Fig. 3, V. These differ- 
ences are then of degree, not of kind. The Ferns above named, whether 
or not they be really related, thus provide one of the best examples of 
transition from the non- 
perforated to the per- 
forated condition, both in 
leaf-trace and in the axial 
stele. 
The anatomical de- 
tails of L. cuspidatus help 
to explain the otherwise 
difficult case of another 
Acrostichoid Fern, Dryo- 
stachyum (. Photinopteris ) 
drynarioides (Hk.), Kuhn. 
It is a Fern of peculiar 
habit of its leaves, but 
with Drynarioid venation, 
and probably closely re- 
lated to Drynaria itself. 
In transverse section the stock shows very numerous meristeles, ar- 
ranged in a manner which may be explained by comparison with 
Z. cuspidatus . It is shown in Text-fig. 11, in which the letters X, Y, z 
indicate leaf-gaps, each with an arch of highly subdivided meristeles. These 
correspond in position and nature to the similarly marked gaps in Text- 
fig. 10, c, of L. cuspidatus. In fact, all that is required for essential similarity 
of the structure of the stock is the higher subdivision of the solenostele itself 
by more numerous perforations than in Z. cuspidatus. These are present in 
D. drynarioides , which is in this respect a. more advanced type. 
With the exception of Metaxya , the Ferns which enter into the above 
comparisons, though they may vary in leaf-outline, correspond in their 
venation. They are reticulate, and fall under either Venatio Anaxeti 
or Drynariae , two schemes which are very closely related. They share 
the character of having small, rather irregular, areolae, with one or more 
