380 Stiles .— The Structure of the Aerial Shoots of 
with that of the stem. Stomata were not observed, and Miss Ford states 
that they are absent from the leaf of P. triquetrum. The interior of the 
leaf is composed of parenchymatous cells continuous with the assimilatory 
tissue of the stem. The cells in the leaf, however, do not possess to any 
marked degree the intercellular spaces characteristic of the outer cortical 
cells of the stem, and in this respect the leaf differs from that of P. tri¬ 
quetrum. They contain, however, conspicuous nuclei and many chloroplasts. 
The leaf-trace, the xylem of which, when it exists, terminates at the 
level of the leaf insertion, is continued into the leaf by some narrow 
elongated cells. These appear to be completely absent from the leaves 
of P. triquetrum. 
4. The Sporophyll. The forked sporophyll has almost exactly the 
same structure as two scale leaves connate at the base. Transitions 
between ordinary leaves and sporophylls are found in which the leaf 
is divided for a part only of its length. 
Between the two prongs of the forked sporophyll arises the sporangio- 
phore, which consists of a short axis bearing, and completely fused with, 
a synangium of three confluent sporangia. In all cases examined a vascular 
bundle supplied the spore-producing member. As a rule about two or 
three tracheides are given off from the ends of one of the xylem arms of the 
stem-stele in exactly the same way as the leaf-trace originates. The 
sporophyll-trace (Fig. 11) passes up through the cortex in much the same 
way as the leaf-trace, and elongated parenchymatous cells pass into the 
two forks of the sporophyll as into the leaf. The xylem does not, however, 
terminate at the level of insertion of the sporophyll, but passes up into the 
axis of the sporangiophore. Here the number of xylem-elements increases, 
so that a section passing transversely through the three loculi also passes 
through a vascular bundle in the axis between them, composed of five 
to eight tracheae. These, however, terminate below the middle of the 
synangium. 
Bertrand 1 states that in P. triquetrum the axis of the synangium is 
completely without vascular tissue, although elongated cells are present 
here. 
The vascular structure of the sporangiophore found in P. flaccidum 
is interesting in comparison with Tmesipteris . In Tmesipteris Miss Sykes 2 
found the sporophyll bundle divided into three, the two lateral strands 
passing one into each lobe of the forked sporophyll, the central strand 
passing into the axis of the sporangiophore. This is similar to what takes 
place in P, flaccidum , only here the sporophyll bundles, like the leaf 
bundles, are represented by a few elongated parenchymatous cells. 
The bundle in the axis of the sporangiophore of Tmesipteris then 
divides into three at the base of the bilocular synangium ; the two lateral 
1 Bertrand, C. E. (’ 83 ), p. 213. 2 Sykes, M. G. (’ 08 ), p. 74. 
