Vascular System of Matonia pectinata . 495 
cylinder is much wider also. The third cylinder is developed in connexion 
with the closure of this second gap, which takes place well in front 
of the node 1 . Of forty-two cases in which a third cylinder occurred, 
only six cases of discontinuity were found. In the first of these cases 
the third cylinder arises as an internal thickening of the mid-dorsal region 
of the second cylinder, immediately after the closure of the gap. Traced 
forwards it soon becomes detached as a protostelic strand which quickly 
dwindles and dies out in the ground-tissue. A little further forward 
in the same internode a third cylinder again arises as an internal thickening 
of the same region, but a little to one side of the mid-dorsal line. It 
becomes free and remains so to the end of the series. The third case 
in another rhizome was exactly like the first. In the fourth case, after 
passing through a node, and coming into connexion with the second 
cylinder at the closure of its gap, the third stra-nd separated again, 
dwindled and died out, appearing again after the next node by a dorsal 
thickening of the second. The fifth and sixth cases were connected 
with the branching of the rhizome ; at the origin of the weaker branch 
the third cylinder, formed from the branching of that of the parent axis, 
died out, but shortly afterwards a fresh one arose freely in the pith. 
In all these cases of discontinuity the third cylinder is protostelic in 
structure. In nineteen cases the third cylinder remains attached to the 
second, as an internal ridge, for some distance in front of the connexion. 
In all of these also the third cylinder is protostelic. So far as they go, the 
cases just cited tend to support the view that the third cylinder of 
Matonia is in its origin an internal elaboration of the gap formed in the 
second, that it bears in fact the same relation to the second as the second 
does to the original stele. The blind ending of the third cylinder is 
not without parallel in other Ferns possessing internal accessory vascular 
strands. It occurs, for instance, in the young plants of Alsophila excelsa 
and in Cyathea 2 . 
We found twenty-two cases altogether in which the third cylinder 
is protostelic in structure, four in which it exhibits, for part of its course 
at least, the Lindsaya-type, and fourteen in which it is solenostelic. Its 
structure frequently varies in a single rhizome from one of these types 
to another, the complexity being greatest in the region of the node. 
Thus in one case the third cylinder is protostelic as far as the node, 
in the course of which phloem appears in the middle of the xylem. In 
front of the node its structure becomes solenostelic, and finally, before its 
junction with the edge of the gap of the second cylinder, it opens and 
becomes protostelic again, though it has enlarged considerably in the 
course of these changes. The following table will show the close relation 
1 Seward (’99), p. 187 . 
M m 
2 G wynne- Vaughan (’03). 
