241 
of Masdevallia muscosa 3 Rchh . f. 
of layers of small prismatic cells from the xylem. These are 
only markedly tannin-containing within the limit indicated by 
the flat wash of colour. As the bundles pass from the blade 
to the neck, their elements undergo a most conspicuous flatten- 
ing parallel to the upper and lower limiting surfaces of this part 
(cf. Figs. 11 d, 11 e, and 11 f). In Fig. 11 e is seen a section 
from the thinnest and most flexible part of the neck, where — 
as we shall see — the maximum amount of bending takes place. 
By this flattening the bundles come to lie in the neutral plane of 
curvature, and offer as little opposition as possible to bendings 
due to variations in the turgidity of the opposing sides. Quite 
the same sort of thing Is found in the pulvinus of Mimosa pudica , 
and elsewhere. The elements of the three bundles in the neck 
are identical with those seen in Fig. 13. The bundles are 
however conspicuously flattened, occupying a much less ver- 
tical range than in the blade. It may be noted that it is here 
similarly accompanied by tannin-containing cells which have a 
wider distribution than in Fig. 13. They extend throughout 
the upper portion of the section, uniting the bundles, and ex- 
tending upwards to the layer below the upper epidermis. 
In the neck the ground-tissue consists of prismatic paren- 
chymatous cells. That below the plane of the bundles is 
thick-walled, giving a rigidity to these parts of importance as 
will appear in the sequel. Above it consists of delicately thin- 
walled cells, with small intercellular spaces ; these thin-walled 
cells extend to the upper epidermis, and are probably the 
seat of contractility. The thick-walled cells of the lower 
half extend between the central and lateral bundles, but not 
beyond the level at which they run. The epidermis on either 
surface is thick-walled and but little cuticularised, that above 
quite plain ; but below, each epidermal cell is drawn out into 
a pointed papilla. The epidermis of the underside of the 
labellum is everywhere drawn out into larger or shorter sharp 
hairs, especially on the ridges over the bundles. The crest of 
the blade is formed entirely of thin-walled parenchyma with 
copious protoplasm. These cells show a well-defined con- 
tinuity of protoplasm when treated with hydric sulphate and 
