702 G wynne- Vaughan Observations on the 
is to be found in the stem of Pteris elata 1 which is an erect or 
oblique rhizome with the leaves arranged radially all round. 
The vascular system is perfectly solenostelic, and the leaf-gap 
closes up immediately after the departure of the leaf-trace. 
The curved leaf-traces are inserted with their concavities fac- 
ing directly towards the apex, which, moreover, appears to 
be always the case in all Ferns in which the stem grows erect. 
The appearance of the internal vascular system will vary 
according to the dimensions of the plant, and to the position 
of the section relative to the nodes (Fig. 14). In a rhizome of 
average thickness the internal system usually has the form of 
a large gutter-shaped strand or of a completely closed cylinder, 
the latter being generally present for some distance below each 
of the nodes. As the leaf-gap is approached from below a 
fairly large flat strand is seen to separate off from the internal 
vascular cylinder, which, travelling forwards and outwards, 
ends by fusing completely and finally with the anterior margin 
of the leaf-gap in the outer solenostele ; just as the latter 
becomes closed up again. The lacuna thus produced in the 
internal vascular cylinder converts it into a gutter which, 
however, gradually closes up in the internode above, so that 
a complete cylinder is again formed, usually for some distance 
before the next leaf-insertion is reached. Sometimes, on the 
other hand, two such gaps in the internal vascular system may 
overlap, so that two separate internal strands are occasionally 
to be met with. 
In large and especially well-grown rhizomes a second 
internal vascular system is to be found lying within the first. 
It is not, however, very highly developed, but consists of a 
single small free rounded strand. This central strand fuses 
with the margin of each of the lacunae in the first internal 
cylinder, but usually separates off again after a little while. 
In fact, it behaves towards the first internal vascular system 
in exactly the same way as the internal vascular strand of 
Dicksonia rubiginosa behaves to the ordinary stelar cylinder. 
1 Pteris elata , var. Karsteniana , Kz., a variety not mentioned by Hooker, was 
the plant actually investigated. 
