12 
DR R. C. DAVIE ON 
function is performed by part only of this abaxial tongue ; the remainder of it goes 
directly to supply the pinna-trace. The supply for the last pinna originates in the 
same fashion in the two Ferns— both ends of the adaxial strand give a contribution to 
the pinna-trace. 
General Discussion and Conclusions. 
The examination of the leaves of Aspidium martinicense, A. trifoliatum, Poly- 
stichum adiantiforme, and Dryopteris grandis has confirmed the opinion stated 
above (p. 9) as a result of the comparison of the leaf-traces of species of Polypodium, 
that the outline of the Fern leaf-trace is directly related to the length of the leaf, and 
that the type of pinna-trace is partly dependent on the size of the pinnae. The only 
species of Polypodium of the series examined with a leaf comparable in length to 
those of the four species just named is Polypodium decurrens. The leaf-trace of 
P. decurrens. has a strongly developed series of strands on the abaxial curve (text- 
fig. If), a feature which we have seen to be prominent in the leaves of the species 
of Aspidium, Polystichum, and Dryopteris (text-figs. 3, 5, and 6). Similarly, in 
Polypodium decurrens and in these four species the pinnae are larger than in any 
of the other Ferns described. It is in these largely-pinnate forms that the abaxial 
curve of the leaf-trace is employed to supply a part of the pinna-trace, additional to 
that which comes from the adaxial strand. 
From these Ferns we may conclude that the abaxial portion of the Fern leaf-trace 
is directly related to the length of the leaf and becomes more prominent the longer 
the leaf. This is confirmed by the comparisons of the Fern leaf- traces figured by 
Borkowski (above, p. 7) and of the leaf- traces of leaves of Polypodium vulgare 
grown under differing conditions (text-fig. 2). 
That the abaxial curve of the leaf-trace may be used directly in the formation 
of the pinna-trace is shown by the largely-pinnate species Aspidium martinicense, 
A. trifoliatum, Polystichum adiantiforme, and Dryopteris grandis. 
But we find the abaxial curve of the leaf-trace directly used in the pinna-supply 
in Leptochilus guianensis (text-fig. 4), which has relatively small pinnse. Such a 
coincidence raises at once the idea that there may be in certain groups of Ferns an 
hereditary tendency to employ the abaxial portion of the leaf-trace in the formation 
of the pinna-trace. It has already been shown (Davie, T4, pp. 369-373) that while 
the extramarginal type of pinna-trace appears to occur regularly in Ferns with large 
leaves, it occurs also in small -leaved Ferns, which are closely related to the large- 
leaved types (loc. cit., p. 354). Three species of Leptochilus have been examined. 
The leaf-trace of Leptochilus guianensis is described above (p. 10 and text-fig. 4) ; 
that of L. cuspidatus (Pr.) C. Chr. was described in a former paper (Davie, T4, p. 352 
and text-fig. 2) ; that of L. triscuspis (Hk.) C. Chr. exhibits a simpler form than 
those of the other two species : it, like them, possesses the “ combination-type ” of 
pinna-trace, but the ends of the adaxial and abaxial strands only are nipped off to 
