240 
Oliver . — On the Sensitive Labellum 
purple (shaded in the Figs.). As it passes into the neck the 
crest, cr., gradually gives place to a shallow groove (seen in 
Figs. 6 and 11 d), which gradually dies out, and the neck — 
bent into a U-shape with the convexity downwards — is band- 
like with perfectly even upper surface (Figs. 3 and 1 1 e). At 
the point where the neck runs into the foot is inserted an 
emergence ( e , Fig. 3) of an interesting nature. This emergence 
arises from the upper surface, and is about 1-5 mm. in length. 
It bridges over the concavity formed by the arching of the 
neck in the extended labellum (Fig. 3). Its tip is bent slightly 
upwards, and does not quite touch the point where neck and 
blade run into one another. Figure 6 shows the extended 
labellum looked at from above ; it will be noticed that the 
neck, h, can be seen between the tip of the emergence and the 
groove at the proximal end of the blade. The foot, from the 
point of insertion of this emergence, gradually increases in 
thickness till it passes directly into the base of the column, 
with which it makes a slightly obtuse angle. 
In Figure 11 I have represented diagrammatically a series 
of transverse sections of the labellum : a, b, c, & c. represent 
sections through the labellum at the points marked a, b , c, &c. 
in Fig. 12. In each the position and form of the vascular 
bundles are indicated. In every case the xylem is shaded, 
the phloem below it being outlined only. In the blade (Figs. 
11 a, 11 b, and 11 c) in each of the three bundles the xylem is 
crescent-shaped, the horns of the crescent embracing, more or 
less, the phloem. The central bundle is drawn in Fig. 13 on a 
much larger scale. This section is taken from a point below the 
centre of the crest (corresponding to Fig. 1 1 c). The crescentic 
xylem consists of spiral tracheides, tr ., which are accompanied 
by a sheath of cells containing tannin to a marked degree. 
The extent of this tannin-containing sheath is indicated by the 
light flat wash carried over the cells (Fig. 13 sh.). All these 
cells have very large and conspicuous nuclei. Below the 
xylem is the small-celled phloem, pk., of sieve-tubes, with 
horizontal and slightly callous sieve-plates, and companion- 
cells. As may be seen, the phloem is separated by a number 
