6 
DR R. C. DAVIE ON 
there is a compact rod of xylem, the edges of which extend slightly and give off 
their margins below the pinnae. In P. cultratum, the leaf-trace of which is 
represented in text-fig. 15, the leaf is much longer than in P. serrulatum, but 
the pinnae are small in proportion to the length of the leaf. The leaf-trace has a 
strong development of tracheides on its .abaxial side. P. polypodioides has a short 
leaf, with relatively long pinnae closely crowded together. Its leaf-trace, figured in 
text-fig. lc, has long lateral extensions of xylem but little or no abaxial development. 
In P. plumula and P. lepidopteris the leaf is longer than in any of the species yet 
mentioned, and the pinnae are short and very numerous. The leaf-traces, represented 
in text-fig. Id,- have only a slight development of the lateral extensions and a strong 
abaxial group of tracheides. The abaxial development of the leaf-trace becomes a 
system' of separate vascular strands in the leaf-traces of P. loriceum, P. catharinse , 
P. brasiliense, and P. fraxinifolium, the type of which is figured in text-fig. le. In 
these Ferns the leaf is longer than in any of the five species described above, while 
the pinnae are larger than the pinnae of these species, in relation to which the lateral 
b 
c d e f 
Text-fig. 1. 
extensions of the adaxial portion of the leaf-trace are prominent. P. decurrens 
has the longest leaf of the whole series ; its pinnae are larger than the pinnae of 
any of the others; its leaf-trace, represented in text-fig. If, has a very extensive 
system of abaxial strands and prominent lateral extensions of the adaxial strand. 
We have thus, in the ten species of Poly podium 'examined! an increasing length 
of leaf and an increasing size of laminar surface. Apparently corresponding to the 
one there is an increasing development of the abaxial side of the leaf-trace, while 
in relation to the other there -is an increasing extension of the lateral portions of the 
adaxial nart of the leaf-trace. 
As one follows in detail the changes in the leaf-trace in any member of the 
group P. loriceum, P. catharinse, P. brasiliense, and P. fraxinifolium, from base 
to apex of a leaf, noting the relations of the various strands one to another, and 
especially the relation of the strands of the abaxial system to the adaxial strand, 
one finds that below the pinnae, and prior to the departure of the margins of the 
adaxial strand as the pinna-traces, there is a movement of the strands of the abaxial 
system towards the adaxial strand and a fusion of those strands of the system which 
are nearest to the adaxial strand with the abaxial ends of that strand. There is in 
the type of leaf-trace shown in text-fig. le a reinforcement of the adaxial strand 
from the abaxial system of strands prior to the departure of a pinna-trace. In the 
case~of the Gavea Beach example of P. brasiliense, which has large pinnae closely 
crowded together on a short length of raehis (Plate, fig. 4) there is a double 
