Anatomy of Solenostelic Ferns. 697 
similar to that described and figured by Mettenius 1 and 
De Bary (loc. cit.) in several different dorsiventral Ferns. 
All the Davallias of the section Humata that were examined 
belong to this type, and also most of those belonging to the 
sections Eudavallia and Leucostegia. In some of these Ferns, 
however, the actual state of affairs is a little obscured by the 
fact that several separate leaf-traces are given off to each leaf, 
which run forward for some distance in the ground-tissue 
of the stem before they turn out into the petiole, also the two 
meristeles of the stem are often so similar to these in form 
and size that they are scarcely to be distinguished from them. 
Attention should also be drawn at this point to the vascu- 
lar arrangement described by Mettenius (loc. cit., p. 552 ) in a 
number of dorsiventral Ferns, of which Platycerium alcicorne 
may be quoted as an example. In these the dorsal meristele 
seems to be present as usual, but the ventral one appears to 
be broken up into an irregular meshwork of strands, the gaps 
in which bear no relation whatever to the leaf-insertion. 
In Ferns which have their leaves arranged radially in 
several rows all round a prostrate or an erect stem three 
or more leaf-gaps usually overlap at the same level, and 
the solenostele is broken up into just as many more or less 
equivalent meristeles arranged in a ring around the axis. 
If the structure is still but little removed from solenostely 
it may happen that two leaf-gaps only overlap at any one 
level, and then the vascular arrangement, when seen in trans- 
verse section, generally consists of a large gutter-shaped 
meristele with another small one lying across its opening 
(Figs. 9 and 10). Although this structure is very similar 
in appearance to that presented by the simpler forms of the 
dorsiventral type, it is really to be regarded as quite distinct, 
because the relative positions of the two steles change in 
accordance with the radial arrangement of the leaves. The 
following Ferns were found to be radially dictyostelic, but 
still remain very close to solenostely: Dicksonia Barometz 
(Fig. 17), P ter is tremula , ere tic a, flabellata , heterophylla 
1 1. c., Taf. vii, viii. 
3 B 2 
