460 Boodle.—Anatomy of the Hymenophyllaceae. 
probably have shown the upper band in a much more advanced 
stage of development. Fig. 3 only requires the completion 
of the upper band to produce the mature structure of Fig. 4. 
In H. scabrum the upper xylem-band is usually separated 
at both ends from the lower by parenchyma, but this is not 
always the case. The early differentiation of the lower 
xylem-band, and the attachment of roots to it, suggest that 
it is at first important for conduction of water to the growing 
apex of the rhizome. 
Hymenophyllum demissum , Swartz, var. nitens (Hort.), also 
has a fair-sized rhizome, the structure of which is very similar 
to that of H. scabrum. Fig. 5 is a diagram of a transverse 
section. Here the outer cortex is sclerenchymatous as well 
as the inner, so that the sclerenchyma {sc) extends from 
epidermis to endodermis. The chief features of the stele 
which differ from H. scabrum are that the upper and lower 
xylem-bands (u, l) are frequently fused at both ends, and 
that the protoxylem {px) is usually not a compact group, but 
is spread out as a horizontal band in the conjunctive paren¬ 
chyma. The xylem, phloem, &c. are lettered as in the 
previous diagram (Fig. 1). The xylem of a root-stele (r) is 
seen on its way in to join the xylem of the rhizome. 
In H. dilatatum , Swartz, var. Forsterianum (Hort.), the 
structure of the rhizome is of much the same type as II. de¬ 
missum , as is seen in the stele on the right in Fig. 9. The 
upper and lower bands are here more frequently free, but 
the protoxylem is usually spread out as a row of tracheides 
in the central parenchyma, as in H. demissum. 
The examples so far described have a rhizome, which is 
comparatively stout for the genus. Species with more slender 
rhizomes have a simpler type of structure, and some of them 
will now be described. 
II. sericeum , Swartz (Plate XXVI, Fig. 13), has a fair-sized 
mass of metaxylem (x) with either one or two protoxylem- 
groups attached to its lower side. The section figured has 
two protoxylems (px). The xylem shows no sign of the 
differentiation into two bands, as seen in the previous types. 
