Species of the Neiv Zealand Orchidaceae . 14 1 
passage cells. In transverse section the endodermis has an open appearance 
due to the presence of two passage cells together and to the large lumina of 
the cutinized cells. Five groups of xylem and phloem are usual. Their 
elements are small and seldom more than six in number. The centre of the 
cylinder is filled with fibres. 
In transverse section the stem is sinuous in outline (PL X, Fig. 58). 
The epidermal cells, which are slightly elongated in the tangential direction, 
have mucilaginous walls. The outer portion of the cortex consists of large 
semi-collapsed cells with scanty contents. The cells of the inner portion 
have firm walls with numerous pits which in longitudinal section are fre- 
quently arranged in a reticulate manner. Chlorophyll is present in this part 
of the cortex and in the ground tissue of the centre of the stem. The vascular 
bundles may have complete sheaths of sclerenchyma, especially if they lie 
towards the periphery. Their elements are numerous but not large. The 
xylem consists only of various kinds of tracheides. 
The leaf is very thick and has rounded edges. Both epidermes are 
wide, the upper exceptionally so. Below it are several rows of cells 
whose shape bears a resemblance to palisade tissue. The general assimi- 
latory tissue consists of somewhat large round cells connected together by 
tubular processes, in the diaphragms of which two to five circular pits are to 
be seen. Of the fifteen vascular bundles the midrib and four others exceed 
the remainder in size. The sheaths are strong, especially on the phloem 
side, where their elements are unusually large. Xylem and phloem groups 
are somewhat small. Spiral and pitted tracheides alone are to be found 
in the former. Single cells containing raphides occur midway between 
the vascular bundles lying towards the leaf edge. Occasionally a club- 
shaped sunken cell with elongated pits in its walls occurs in the upper 
epidermis. Beneath it the ‘ palisade ’ cells fit more closely than usual. On 
the upper surface each cell of the epidermis is produced into a stout 
papilla over which the thick cuticle is continued. The appearance of the 
upper half of the leaf is suggestive of water storage. Large vacuoles 
are present in the protoplasm of the epidermis ; pits occur in the walls, 
especially in those separating two adjacent epidermal cells. In the ‘pali- 
sade * region vacuoles are numerous, though smaller ; pits are of frequent 
occurrence ; the number of chlorophyll granules is small in comparison 
with that in the lower portion of the leaf. Mucilaginization of the walls 
occurs throughout ; it is most marked in the epidermis, weaker in the 
‘ palisade ’ region, and least in the general cells of the lower part of the leaf. 
In the pseudo-bulb the vascular strands follow one of two courses. 
Those originating in the upper portion of the stem usually run to the apex 
with but slight deviation ; those, however, which come from the side of the 
stem bend outward and follow the contour of the pseudo-bulb at a little dis- 
tance from its edge. Just below the apical cavity they unite to form the 
