244 Oliver. — On the Sensitive Labellum 
Mechanism of movement. — From direct observation and 
experiment it seems that the cells concerned in this move- 
ment are confined to the upper half of the band-like neck. 
As in Mimosa piidica so here, in the contractile region there 
is a sudden loss of turgidity by the cells on that side towards 
which the movement occurs. We have here to deal with a 
case not common in the vegetable kingdom, and which finds 
its parallel in Dionaea. There is a complete differentiation 
between the parts which receive the stimulus, i.e. the crest of 
the blade, and the parts which carry out the movement, i.e. 
the neck. Further, the part where the contractile cells reside 
is in no way responsive to direct stimulus. Thus, if the upper 
surface of the neck be at any point touched gently with a hair or 
other body — such touch being amply sufficient to cause a con- 
traction if applied to the crest direct — no contraction follows. 
In other plants there may be often a conduction of stimulus 
over some distance, but usually the part to which the stimulus 
is conducted is itself directly sensitive to external shock. 
Thus for instance in the stamens of Sparmannia africana , if 
any stamen be directly stimulated, it not only itself con- 
tracts, but also transmits the stimulus to other stamens, which 
likewise contract ; so also in the stigmatic lobes of Martynia. 
In both these cases the part to which the stimulus is trans- 
mitted is also itself sensitive to an external stimulus. In 
Dionaea , however, a separation similar to that in our Mas - 
devallia is found. In Dionaea sensitiveness to an ordinary 
touch is confined to the six tactile emergences on the upper 
surface of the leaf — three on each valve ; the organ of move- 
ment (the hinge) is at some distance. 
Fig. 3 shows the labellum in the extended position. On 
stimulating the crest the blade traverses an angle of some io° 
slowly before developing the final rapid contraction. During 
the first period the blade is — so to speak — rounding the 
emergence. Any sudden contraction, with the parts as 
arranged in the figure, would result in the blade being jammed 
by the emergence. Such jamming occurs if the emergence be 
a trifle too high, as may be obtained by previous manipulation. 
