188 MR. P. GROOM—CONTRIBUTIONS TO THE 
parenchyma, some narrow sieve-tubes and companion-cells. 
The xylem, in contrast to that of the root, contains a protoxylem 
formed of spiral, tangled, or annular vessels. In addition there 
are tracheides with transverse pits. 
(B) Higher up, where the leaves are separated by long inter- 
nodes, the axis is considerably thinner than at the base. 
(1) The epidermal cells have very much thicker walls (Pl. V. 
fig. 8). There is an extremely thick cuticle. The outermost 
layer of the wall is coloured deep brown; within this the outer 
wall and the lateral and inner walls are suberized and are pale in 
tint. Only very few stomata occur in this region. (2) The 
number of cortical parenchymatous cells with thin cellulose-walls 
has diminished to one. (3) The general sclerenchymatous sheath 
is made up of three to four layers of fibres with enormously 
thickened, glistening, stratified, pitted walls, and small lumina. 
(4) The stelar conjunctive tissue is sharply marked off from the 
general sheath, and consists of elongated parenchyma-cells with 
thin walls. The scattered vascular bundles are small. (5) The 
vascular bundles are collateral, but possess no sheaths of their 
own. The phloém is well developed, and is separated from the 
xylem by a layer of elongated parenchyma, the cells of which 
have thin, pitted, cellulose-walls. In the larger central bundles 
protoxylem in the form of spiral vessels is embedded amongst 
elongated narrow parenchymatous cells [phloém (P): I saw no 
sieve-tubes amongst these]. 
Ci.) Histology of the Rhizome. 
Compared with the base of the inflorescence-axis the rhizome 
possesses more numerous leaves, and from it radiate numerous 
roots. The vascular bundles running out to these complicate 
the structure of the ;hizome. Compared with the floral axis, all 
the constituent cells are shorter in an axial direction, more 
numerous layers of the cortex have their walls lignified, so that 
there remains but one cortical layer with walls of cellulose. In 
the vascular bundles the xylem (tracheides and spiral vessels) is 
developed better than in any other part of the plant. 
Gu.) Structure of the Scales. 
The scales have sheathing bases which are pressed against the 
axis. Each consists of an upper (inner) epidermis, a lower 
