242 Oliver . — On the Sensitive Labellum 
Hoffmann’s blue 1 . The fine uniting-strands show at the pit- 
closing membrane a swelling which, although I was unable to 
resolve it, no doubt represents a small spindle-like arrange- 
ment of very delicate filaments perforating the closing-mem- 
brane in a sieve-plate-like manner, and so uniting the strands 
from the respective cell-bodies (see Fig. 14). Gardiner 2 gives 
cases in which he met with a similar appearance due to the 
same cause. In the ‘ tannin-containing sheath ’ and in the 
neck a similar continuity exists. 
The emergence, previously referred to, merits fuller notice. 
It is entirely non-vascular, originating simply as an outgrowth 
of the upper surface at the junction of foot and neck, and 
involves only the ground-tissue and epidermis. Fig. 11 g is a 
section of the foot above the point of insertion of the emergence, 
Fig. 11 f, just below. In Fig. 11 f transverse sections are given 
of both emergence (above), and neck (below), showing their 
relative position to one another. In Fig. 17 is seen a much-en- 
larged longitudinal section of the emergence with its upturned 
tip. The epidermis alone is fairly thick-walled, giving a certain 
elasticity to it, so that if the emergence be deflected down- 
wards with a bristle, when the labellum is in the extended 
position, till it touches the neck, it will, on removing the 
deflecting force, immediately fly back to its former position. 
Irritability and Movement. 
The movement is displayed as a sudden and rapid fold- 
ing up of the labellum on its band-like neck, so that the 
broad distal part of the blade is approximated to the top 
of the column (Fig. 4). The general view of the flower 
(Fig. 1) shows it with contracted labellum. This movement 
is called forth by the gentlest touch of a hair or insect’s foot 
on the median crest of the blade. No other part of the blade 
is irritable in this way. Irritability is thus confined to the 
upper surface of the blade, and of this to some part of the 
1 Gardiner, On the Continuity of the Protoplasm, &c., in Phil. Trans. 1883, Part 
iii. p. 824. 
2 Loc. cit. p. 833 ; cf. PL 68, Fig. 5. 
