428 Browne. — A Fourth Contribution to our Knowledge of 
height of the stele was measured from a point just below the insertion of the 
annulus to the level, above the last whorl of sporangiophores, at which the 
vascular structure characteristic of the extreme apex of the cone is 
established. 
II. General Description. 
The cone of E. sylvaticum more closely resembles in its anatomy the 
cones of E. arvense and E . maximum than those of the other species studied. 
The resemblance is closest to the cone of E. maximum. The radial extent 
of the axial xylem is slight ; except in the neighbourhood of the rather more 
deeply seated groups of protoxylem, the metaxylem is usually only one to 
two (often only one) cells in depth. Moreover, a few parenchymatous cells 
are not uncommonly interspersed in the tracheides of the metaxylem, though 
in the species under consideration this intercalation of parenchyma among 
the tracheides is not as extensive as in E. maximum. Nevertheless, in 
a transverse section of the cone oiE. sylvaticum, the general resemblance to 
the cone 6f E. maximum is striking, especially, of course, to the smaller 
specimens of the latter species. The wide stele, the relatively numerous 
strands, the small radial extent of the metaxylem, its interruption by 
parenchyma, the small size of the traces, the presence and distribution of the 
tannin cells, all these characters in combination vividly recall the cone of 
E. maximum. But, relatively to its size, the cone of E. sylvaticujn has 
a better developed vascular system. For instance, in the cone of the latter 
species the protoxylem generally abuts throughout most of its course on the 
metaxylem, whereas in E. maximum a few parenchymatous cells intervene 
in the internode of the cone between protoxylem and metaxylem (cf. Barratt, 
p. 224, Text-fig. 21). 
Though typical endodermal markings are not well shown in the axis of 
the cone a common outer endodermis can be distinguished, comparable 
to that of the ordinary stems. There was no trace of a common inner 
endodermis, such as Pfitzer found in the rhizome (Pfitzer, pp. 313-14). 
The tracheides of the cone of E. debilc are of the usual type. Though 
bands of xylem occur locally (cf. Text-figs. 3-6) many of the strands 
are very narrow (PI. XXI, Fig. 7). In mature specimens, such as Cone A, it 
is often the case that some of the bundles in a transverse section of the axis 
have well-marked carinal canals, perhaps nearly half the size of the bundle, 
while in their immediate neighbours the disintegration of the protoxylem is 
only beginning. The metaxylem varies a good deal in amount. It is 
usually narrow laterally, so that the strands are widely separated and 
parenchymatous cells are interspersed among the tracheides. There is 
sometimes a tendency for tracheides obviously belonging to the metaxylem 
to be almost or quite as deeply seated as the protoxylem (cf. PI. XXI, Fig. 7, 
especially the large bundle). When the strand is narrow its outline tends to 
