43i 
some Species of G leichenia. 
The problem of the origin of solenostely in G. pectinata cannot 
be satisfactorily solved at present, but it appears probable that the 
derivation from protostelic structure may have been somewhat as follows : — 
1. Mertensia- type of protostele with nodal islands. 
2 . Enlargement of stele in connexion with increase in size of arched 
leaf-trace. 
3. Replacement of central part of xylem by a medulla. 
4. Formation of ramular gaps. 
5. 4 Intrusion’ of phloem, &c., at ramular gaps. 
6. Extension of these internal tissues throughout the length of the 
rhizome. 
7. Formation of foliar gaps completing the solenostelic structure. 
It is not easy to find any physiological advantage which the plant gains 
by its solenostely, apart from convenience of attachment for the phloem 
situated on the inner side of the hooks of the leaf-trace (see PI. XXIX, Figs. 
6 , 5). Working on the suggestion that the presence of internal phloem 
might mean an additional amount of this tissue, the area of the phloem and 
xylem was measured in camera lacida drawings of G. pectinata and 
G. flabellata ; it was found, however, that though the area of the xylem in 
G. pectinata was double what it was in G. flabellata , yet the area of the 
phloem in the two cases was approximately the same. Thus, as regards 
proportional amounts, a distinctly negative result was obtained, but possibly 
the possession of internal phloem may have carried some advantage at an 
earlier stage in evolution, e. g. when ramular gaps but no leaf-gaps were 
present, if such a state of things existed. 
Summary. 
Gleichenia pectinata shows regular solenostelic characters. The upper 
and lower protoxylem-groups differ in their degree of immersion in the xylem. 
The structure of the node is similar to that of G. flabellata, but with 
the further complications due to the presence of leaf-gaps and solenostely. 
A nodal pocket is present ; it is free in its lower portion, where it shows the 
typical structure of a nodal island, and in its upper course its different 
tissues become confluent with the corresponding internal tissues of the 
solenostele in relation to the formation of the foliar gap. 
One curious feature at the node is the occurrence of a short disconnected 
strip of phloem-elements on the abaxial side of the nodal island ; this may 
be considered as the remnant of a once continuous band of phloem, which 
formerly filled the gap at present existing in the phloem on the adaxial side 
of the xylem in the petiolar bundle. 
In a node of G. circinnata var. semivestita a protoxylem-group was 
found to have a blind ending basally. 
The rhizome of G. pectinata branches in two ways, monopodially in the 
