222 DR. M. T. MASTERS ON THE MORPHOLOGY 
pitted cells, mingled with which in great abundance are pitted 
and barred ducts in groups of three to six, each group of vessels 
forming a centre around which the cells just mentioned are 
disposed. 
Culm.—An examination of the structure of the stem of R. fer- 
ruginosus, Link, reveals an epidermis of somewhat quadrangular 
cells, destitute of chlorophyll, and having a few scattered stomata, 
protected by two oval guard-cells. In old stems the epidermal 
cells increase greatly in size, and become very thick-walled, espe- 
cially on the outer side. Many of them contain masses of a dark- 
brown substance, probably of aresinous nature. Not unfrequently 
the outer wall of these resin-bearing cells breaks away, leaving a 
funnel-shaped cavity, which being open externally becomes filled 
with dirt. These funnel-shaped cells give a very peculiar appear- 
ance to the microscopic sections of the old culms (Pl. XIV. 
figs. 1, 2). 
Beneath the epidermis in the young culms there is a series of 
small spherical cells containing chlorophyll (Pl. XIV. figs. 3, 4), 
but as they increase in age their size and form become greatly 
changed, their chlorophyll disappears, and thus at length in the 
old culms they form a thick spongy layer of flattened elongated 
cells, whose long diameter is at right angles to that of the culm 
(Pi XIV. figs. 1, 2). 
Succeeding this spongy layer, going from without inwards, is 
another zone of cellular tissue, consisting of three or four rows of 
oblong somewhat quadrangular cells, whose long diameter is 
parallel to that of the culm. These enclose a broad zone of thick- 
walled liber-cells ; interspersed among these latter are numerous 
scattered fibro-vascular bundles. Next in order is a cylinder of 
cellular tissue, whose constituent cells are large, oblong or some- 
what polygonal, and pitted, thus greatly resembling the pith-cells 
of an Exogenous plant. These pith-like cells contain numerous 
small oblong starch-grains, and some of them also enclose dark- 
brown resinous matter like that of the epidermal cells. Traversing 
this pith-like cylinder are scattered bundles of vascular tissue, 
consisting of wood-cells and barred ducts. Pitted ducts and spiral 
vessels seem to be entirely absent (Pl. XIV. figs. 1, 2). 
The sheaths present from without inwards an epidermal layer 
of large, somewhat cubical cells, thickened on the outer wall, and 
perforated here and there by stomata, like those of the culm. 
Subjacent to this is a quantity of cellular tissue, the cells of which 
vary considerably in size, but are mostly oblong and six-sided. 
