196 
A. G. Tansley. 
leaf-gap is approached from below a fairly large flat strand is seen 
to separate from the internal vascular cylinder, and travelling 
forwards and outwards, fuses completely and finally with the 
anterior margin of the leaf-gap of the outer cylinder just as the 
latter closes up. The departure of this flat strand converts the 
cylinder into a gutter which gradually closes up in the internode 
above, so that a hollow cylinder is again formed. But sometimes 
the next gap is formed before the last is closed, so that a 
dictyostelic structure is produced in the internal cylinder. In large 
and well-grown rhizomes a second internal vascular cylinder is to 
be found lying inside the first. It consists simply of a small free 
rounded strand (Fig. 59), which fuses with the margin of each of 
the gaps in the internal cylinder, but separates again very soon. 
In fact it behaves towards the internal cylinder exactly as the 
internal strand of D. rubiginosa behaves towards the primary 
cylinder. In some cases the connexion of the strand with the 
internal cylinder is made by means of a branch which terminates 
at the gap. In rhizomes of medium size the edges of the gaps of 
the internal cylinder are simply thickened like those of the soleno- 
stele of D. ndinntoides. 
In the genus Matonia the structure of the vascular system is 
essentially the same. In M. sarmentosa there arc two concentric 
cylinders in the internode; the internal one is sometimes “ haplo- 
stelic ” and sometimes solenostelic. The structure of the node has 
not been examined, but there can be little doubt that the internal 
cylinder connects with the outer one either directly or by a branch. 
Matonia pectinata. The structure of the complicated vascular 
system of this Fern is worth describing in some detail, because it 
has been thoroughly worked out (Tansley and Lulham, ’05), not 
only in the adult rhizome but in the young plant, and the result 
shows a gradually increasing elaboration of structure, the course 
of which fully bears out Gwynne-Vaughan’s interpretation of the 
series of cases met with in Dennstcedtia and in Pteris data. 
Although the ontogeny of the vascular system of Ferns will be 
dealt with in a later lecture, it is convenient to consider that of 
Matonia pectinata in connexion with the adult structure. 
The stem of M. pectinata is a subterranean creeping rhizome 
with distichous leaves arising in a dorsolateral position. In the 
large rhizomes of the adult plants, however, the leaf-traces occupy 
a dorsal position and are practically monostichous. 
The stem of the very young plant contains a simple slender 
