SinnotL — The Evolution of the Filicinean Leaf -trace. 169 
Ophioderma and possibly Cheiroglossa of the last genus, the foliar supply 
consists of several bundles even at its attachment to the cylinder. This 
condition is quite generally agreed to be a specialized and not a primitive 
one. Unlike that of the Osmundaceae, however, the leaf-bundle in this 
family does not long remain unbroken, but is soon divided into a series of 
strands which become variously disposed. The single protoxylem cluster 
at the base of the trace, which tends to be stretched out parallel to the long 
axis of the bundle, is at first in a clearly mesarch position (Fig. 13) in 
Helmin thostachys (in other characters the most primitive member of the 
family), but soon becomes entirely endarch, a condition which is apparently 
the only one ever found in the other two genera. Both the leaf-trace and 
the petiolar bundle seem to be usually collateral, though they are concentric 
in certain cases. 
I11 this first group of the ferns, therefore, a single and probably con- 
centric strand, with one mesarch protoxylem group, seems to have been the 
primitive state of the leaf-trace, and so, very probably, of the whole petiolar 
system (Text-fig. 1). 
In the second main subdivision of the Filicales, comprising those ferns 
with primitively diarch traces, there is but one family, the Marattiaceae, 
which is represented by five genera : Marattia, Danaea , Kaulftissia , Arch - 
angiopteris , and Angiopteris. In the first four of these, the leaf-trace departs 
from the cortex in much the same way, and consists at its base of two con- 
centric strands, from circular to elliptical in outline, which arise from the 
sides of the gap, and each of which possesses a single cluster of protoxylem. 
As these traces pass through the cortex they begin to divide, and in the 
base of the petiole there are many bundles arranged in an arch. In 
Angiopteris , however, the whole stele is very intricate and the foliar supply 
is inserted on it in a complex manner. The trace consists at its base 
of a large number of bundles which are given off in the form of a rough 
arch, and each of which is concentric and possesses one to three protoxylem 
clusters. It is noteworthy, however, that in young plants of Angiopteris , 
Farmer and Hill (13) found at the base of the leaf the typical double bundle 
of the other genera. 
The position of the protoxylem in the leaf is variable. In Arch- 
angiopteris , Gwynne-Vaughan found the trace, through its whole extent, to 
be endarch (16). In Angiopteris , there is always a protoxylem group on the 
adaxial side of every bundle while it is in the cortex, and there are often 
others in a mesarch position, but in the petiole all the groups are apparently 
endarch. Marattia shows a uniformly endarch condition throughout the 
whole vascular system of the leaf. In Danaea , however, distinct centripetal 
elements were found in the petiole by Brebner (9). This observation was 
confirmed by the writer, and, in addition, the protoxylem in the two bundles 
at the base of the trace was found to be mesarch in more than half the cases 
