The Anatomy of Nephrolepis volubilis J.Sm. 255 
several times longer than broad, with horizontal or oblique end-walls, 
probably forming a connected system. The cells store abundant 
oval starch-grains in the mature parts of the stolon. The metaxylem 
elements are all finely scalariform and develop centripetally, the 
larger tracheids being nearer the centre. The protoxylem consists 
of narrow annular and spiral tracheids grouped in 7-9 distinct exarch 
strands forming the ridges on the xylem-cylinder. Each protoxylem 
strand is traversed by one or two longitudinal rows of parenchyma 
cells. 
The phloem is continuous round the xylem, and the proto- and 
meta-phloems are easily distinguishable on account of the much 
larger elements of the latter. Taking the metaphloem first, the 
sieve-tubes occur in distinct crescentic groups occupying the bays 
between the protoxylem ridges, and separated from the latter and 
from the metaxylem by one or two layers of parenchyma. The 
largest sieve-tubes of each group occur in the middle of each bay. 
Their walls are thin and give the cellulose reaction with chlor-zinc- 
iodine ; the contents are scanty and often closely applied to the walls 
in a thin layer containing the usual refringent granules, which 
become yellow with this reagent. The granules were sometimes 
seen filling the whole cavity of the sieve-tubes, but were often 
aggregated against the walls in groups which seem to mark thin 
places, though neither callus nor sieve-pores were visible. The 
phloem-parenchymatous cells are few in number and, in sharp 
contrast to the sieve-tubes, are full of cytoplasm and possess large 
deep-staining nuclei. The protophloem lies immediately outside 
the metaphloem, forming a well-defined layer of narrow cells about 
2-4 deep. It closely follows the contour of the metaphloem, passing 
over the protoxylem ridges as a continuous wavy mantle (well seen in 
PI, IV, fig. 1). But for this continuity round the protoxylems the 
the structure of the stolon would be remarkably root-like. 1 
The shallow bays in the protophloem are filled up by the thin- 
walled pericycle, which is 4-5 cells thick at the bays, but only two 
cells at the ridges so that its outer limit is circular. 
The endodermis is a single layer of tabular cells with their 
radial walls approximately in seriation with those of the outermost 
pericycle layer. These walls are not thickened but stain yellow 
with chlor-zinc-iodine. In older parts of the stolon all the endoder- 
1 So long as this continuity exists no doubt can be entertained regarding 
the cauline nature of the stolon. In this relation, Heinricher’s simple 
experiments (Flora, 1907, pp. 57, 63, 72) are valuable as being in the nature of 
demonstrations. See p. 266 below. 
