THE LEAF-TRACE IN SOME PINNATE LEAVES. 
9 
trace as there is in different species of the same genus. Throughout the genus there is 
a strict adherence to one method of nipping off the pinna-trace ; there is a gradual rise 
and development of an abaxial system in the leaf-trace as one passes from shorter to 
longer types of leaf ; the abaxial system is as a rule used indirectly in the supply of the 
pinna vascular system, being employed to reinforce the strands from which the pinna- 
trace is nipped off ; in leaves with very large pinnae the pinna-trace is itself provided 
with an abaxial system derived directly from the abaxial system of the leaf- trace. 
We must now see how far the canons thus established for the genus Polypodium 
are applicable to other genera of Ferns. Leaves of some species of other genera 
were collected in Brazil in the localities which supplied the ten species of Polypodium 
described. 
The Leaf-Traces and Pinna-Traces of Aspidium martinicense, Spr. 
and A. trifoliattjm (L.) Sw. 
In Aspidium martinicense , Spr. and A. trifoliatum (L.) Sw., large-leaved Ferns 
found in the rain-forest on the Serra da Carioca, near Rio de Janeiro, the leaf- trace 
is composed of two adaxial and three or four abaxial strands (text-fig. 3a, c). The 
a b o 
Text-fig. 3. 
adaxial strands are unhooked. The pinna-trace comes partly from the margin of the 
adaxial strand (text-fig. 36) and partly from the strand of the abaxial series nearest 
to the pinna to be supplied. The portion of the pinna-trace from the abaxial system 
is nipped off first (text-fig. 36), and moves towards the adaxial corner of the petiole, 
where it is joined by the strand derived from the margin of the adaxial strand (text- 
fig. 3c). (Occasionally the abaxially-derived strand may join the adaxial strand on 
its abaxial face in a common endodermis.) Then it moves out into the base of the 
pinna, and is followed by the margin of the adaxial strand. The latter commonly 
divides into two strands, making with the abaxially-derived strand a three-stranded 
pinna-trace. The double derivation is evident even in the supply to the terminal 
pinnae. The small strand a of text-fig. 3a is derived from the abaxial end of the 
adaxial strand. After the pinna-trace goes off (text-fig. 3c), or sometimes even 
while the pinna-trace is being separated from the parent strands (text-fig. 3a, 6), 
it moves from the adaxial strand towards the corner strand of the abaxial curve and 
fuses with it. Such a reinforcement, however, is not always found in the two species. 
It is most pronounced in the petiole of the longest and most heavily-pinnate 
specimen of A. martinicense ; only traces of it appear in the leaves of A. trifoliatum ; 
it is absent in the shorter leaves of A. martinicense , which have pinnae rather smaller 
than those of the long leaves. 
TRANS. ROY. SOC. EDIN., VOL. LII, PART I (NO. 1). 2 
