4 
DR R. C. DAVIE ON 
apex of the leaf. The leaf-traces of three leaves of P. brasiliense and a leaf of 
P. fraxinifolium are represented in the Plate, figs. 5, 6, 7, 8. Though the leaves 
from which the sections photographed were prepared were collected in very different 
surroundings, their pinna-traces were uniformly of the marginal type. This was to 
be expected if the results of the earlier investigation of some representatives of the 
genus Polypodium were to hold good for the whole genus. In a previous paper 
(Davie, ’14, pp. 354, 358) it was shown for five species of Polypodium (including 
examples of P. brasiliense, grown in the Fern House of the Royal Botanic Garden, 
Edinburgh) that the pinna-trace always left the leaf- trace in marginal fashion. We 
are now able to conclude that the type of pinna-trace is not dependent, in the genus 
Polypodium, upon changes in the natural surroundings of a member of the genus. 
Different environments, as we shall see below, have a marked influence upon the 
leaf-trace in the genus : as far as we may conclude from the jexamination 'of a few 
species of Polypodium grown under natural and artificial conditions, the type of 
pinna-trace is independent of the environment of the leaf in which it occurs. This, 
certainly, is interesting in view of the admitted “naturalness” of the genus 
Polypodium (cf. Copeland, ’07, p. 71). Transverse sections of the leaf-stalks of the 
forest, rock-face, and sand plants of P. brasiliense and of the leaf-stalk of P. 
fraxinifolium are figured in the Plate. These exhibit quite marked reactions to the 
conditions in which the plants were growing. In the plants found near the sea- there 
is a greater number of strands in the leaf-trace than in those found in the forest, 
while the individual strands are larger in the former {cf figs. 7 and 8 in Plate with 
figs. 5 and 6). The most curious feature of these sections, however, is in their 
adaxial vascular strands. In these strands in the Gavea Beach (Plate, fig. 8) and 
Praia de Leblond plants (Plate, fig. 7) the tracheides are rather more numerous than 
in those of the forest plants (Plate, fig. 5, and cf fig. 6 of P. fraxinifolium). In the 
leaf-traces of the latter group, large water-storing cells are prominent, close to the 
lateral parts of the phloem surrounding the central group of tracheides (Plate, figs. 5 
and 6). In the Gavea Beach and Praia de Leblond leaves the water-storing cells are 
replaced by ordinary parenchymatous cells, and the space devoted to them in the 
forest leaves is taken up by a greater development of tracheides (Plate, figs. 7 and 8). 
An exactly similar contrast occurs between the leaf-trace strands of P. loriceum, 
which was found growing in the forest, and those of P. catharinas — a Fern so similar 
to P. loriceum as to be almost indistinguishable from it, — which was found in exposed 
spots on the restinga at Praia de Leblond. The leaves from the restinga were 
perhaps slightly shorter ; the individual pinnae were a little longer, and were more 
closely crowded together. The water-storing tissue and the decreased amount of 
xylem in the forest leaves of P. loriceum, in contrast with the exposed leaves of 
P. catharinse, are as conspicuous as in P. brasiliense and P. fraxinifolium. 
The evidence of modification in the structure of the vascular strands in these 
Fern leaves in relation to their environment agrees as regards the xylem with what 
