6o 
Scott . — (9^ 0 Palaeozoic Fern , 
families with which an affinity has been recognized by most investigators, 
from Renault onwards. 
Though the branching of Zygopteris Grayi and its allies is not 
a dichotomy, it may have originated from a dichotomy, the association of 
the smaller branch with a subtending leaf being a derivative condition. 
On this view the equal dichotomy of Z . corrugata would be the more 
primitive state, as seems natural. On the other hand, it is not impossible 
that the case of Z. corrugata may be one of modified axillary branching. 
I hope to return to this question in a subsequent paper. 
The Morphology of the Aphlebiae. 
Both Renault and Stenzel regarded the scale-leaves which they dis- 
covered in Zygopteris Brongniartii and Z. scandens respectively as abortive 
or reduced leaves, and therefore as comparable to the normal foliage-leaves 
of the plant. This view is no longer tenable. In Z . Grayi , as we have seen, 
the scale-leaves (aphlebiae) occur on the leaf-base as well as on the stem ; 
their vascular strands are given off from the leaf-traces of the foliage-leaves 
and are not independent leaf-traces. Dr. P. Bertrand’s view that the scales 
have the value of secondary petioles seems fully justified (P. Bertrand, ’ll, 
p. 53). Their vascular strands are included by him under the name ‘ sorties 
hatives i. e. they are secondary strands given off ‘ in a hurry ’ or below the 
point where the normal pinnation of the leaf begins. We have seen above 
that the structure of the aphlebia-strand is not unlike that of the secondary 
or tertiary rachis-strands in allied species, and that its mode of emission 
appears to be the same. The aphlebiae, then, are best regarded as modified 
pinnae of the leaf which have spread downwards on to the stem, but are 
always in definite relation, by their vascular strands, with the leaf-traces. 1 
That they are modified is shown by the fact that their lamina contains two 
or three bundles (resulting from the division of the single supply-strand), 
while in all allied plants the normal pinnae are monodesmic. The function 
of the aphlebiae may have been a transitory one, the protection of the 
growing points and young leaves ; in fact, they may well be analogous to 
bud-scales, which are often of the nature of stipules. The aphlebiae them- 
selves might be described as multiple stipules. 
Dr. Bertrand’s observations appear to have cleared up the mystery 
which once hung about these curious organs ; we need no longer feel tempted 
to interpret them as representing an ancestral form of foliage such as the 
phylloids of Lignier, which hypothetically once covered the thallus before 
its differentiation into stem and frond. 
It is very interesting to find that aphlebiae have now been discovered 
1 It is true that the aphlebia-strands are given off in two rows from each peripheral loop of the 
trace (unlike the pinna-strands of the Ankyropteris leaf); no two aphlebia-bundles, however, appear 
to be given off at the same level. 
