Ontogeny. 
13 
The early appearance of the internal accessory strand is 
probably to be attributed to the “ working back ” of the polycyclic 
condition into the very young plant. It is well known that a 
constant thoroughly established character in an adult organism 
tends to be inherited at earlier and earlier stages of the life history, 
and there can be little doubt that this is what has occurred in the 
present case. We can hardly suppose that the internal accessory 
strand was present when the ancestors of Matonia were in the 
monocyclic Lindsay a condition with a very simple type of leaf-trace. 
This is a good illustration of one type of the overlaying of the 
phylogenetic history as recorded in the ontogeny, by the supervening 
of new or “ coenogenetic ” characters as they are sometimes called. 
The adult Matonia pectinata is still oscillating, so to speak, 
between the dicyclic and the tricyclic conditions, the third cylinder 
being a comparatively new development. It only appears in the 
largest rhizomes and is often discontinuous, but it bears exactly the 
same relation to the second cylinder as the second does to the first. 
In correspondence with the increasing size of the vascular system 
it may exhibit the protostelic, the Lindsay a-, or the solenostelic type. 
The leaf-trace of Matonia pectinata passes through an 
ontogenetic series of stages starting with a simple iso-diametric 
strand and ending with the complicated arch with spirally coiled 
free edges characteristic of the adult form. This series of stages 
runs pari passu with the increase in complexity of the vascular 
system of the stem, the incurved edges of the trace being entirely 
supplied by the second internal cylinder. As we saw in the first 
part of this lecture these incurved ends of the trace are separated in 
the sympodial branches of the frond as internal accessory strands 
which contribute to the formation of each successive pinna-trace. 
Their development is probably to be correlated with the shortening 
of the sympodial branch-system of the frond and the consequent 
neccessity of supplying the successive “ pinn se ” in very rapid 
succession. It is to the demands of the pinnae and ultimately of 
the transpiring lamina that we must look, as has already been 
indicated, for the ultimate stimulus to the increased complication of 
the vascular system of the stem. 
It is to be regretted that we have as yet but little information 
as to the gradual increase in complexity of the successive leaf- 
traces of other ferns with elaborate vascular systems. We may 
expect that such information would throw much light on the ultimate 
factors in the evolution of such types. 
