5 
The Leaf-Trace. 
Ferns whose petioles exhibit highly developed complications of the 
sort. The very large fronds of such forms as some species of 
Gleichenia and Lygodmm at first sight seem to contradict this 
conclusion, but it must be remembered that these fronds with their 
dichotomous branching have the assimilating laminae scattered over 
a much greater length of rachis in proportion than the comparatively 
concentrated fronds of such plants as Matonia and the Cyatheaceae. 
It is the crowded insertion of numerous large pinnae that demands 
a great increase of the vascular supply-channels of the petiole, and 
in the sympodial branches of the frond of Matonia pectinata, on 
which the successive pinnae are very closely crowded, the con¬ 
tinuations upward of the incurved free ends of the petiolar strand 
are actually detached as separate internal systems which con¬ 
tribute to the successive pinna-traces (Fig. 96). 
Fig. 96. Matonia pectinata. Diagrams of successive transverse sections 
through upper part of young frond, showing the breaking up of the petiolar 
strand, and the successive formation of pinna-traces from the sympodial 
strands on each side. It will be seen that the peripheral pinna-traces are 
derived from the ventro-lateral angles, and from the incurved free ends of the 
petiolar strand (the latter being detached and enclosed within the sympodial 
cylinders as accessory internal systems), both of which parts represent the 
latest complications of the petiolar system. From Seward. 
The petiolar system of the Cyatheaceae is very characteristically 
broken into a number of kidney-shaped strands—“divergents” as 
they are called by Bertrand and Cornaille—each with one proto- 
xylem (Fig. 69). In the less highly developed forms this breaking is 
incomplete, though the outline of the curve is waved, the waves cor¬ 
responding with the successive divergents. The continuity of the 
curve is also commonly broken at the bottom of each lateral fold, the 
ventral (upper) limb of each fold sometimes becoming continuous 
with the corresponding limb on the opposite side so that the petiolar 
system is separated into two curves, both facing towards the ventral 
(upper) surface. Each pinna-trace is inserted on both limbs of the 
