252 Oliver . — On the Sensitive Lab el him 
flower-stalks (Figs. 1 and 2), these keep off undesired insects 
which might otherwise interfere with the mechanism. I have 
often watched ants trying to climb up, but they never got 
beyond the first bracteole (br 1 ). The emergences are of 
course discontinuous at this point, and the ant finding them 
beginning again usually desists. 
I have not yet mentioned that at night the labellum assumes 
a position of ‘sleep,’ identical with that of contraction. I 
have repeatedly found that labellums which were ‘down’ at 
dusk w r ere ‘ up ’ by 10 p.m., though I have never had the good 
fortune to find them in a partially closed condition. The 
sleeping here may be to protect the delicate mechanism from 
hurt by nocturnal radiation. 
On one occasion the plant was placed during the day-time 
for several hours (from 11 a.m — 3 p.m.) in a dark chamber. 
The labellums remained, however, in the extended position 
throughout the whole time. 
Jodrell Laboratory, Kew. 
EXPLANATION OF FIGURES IN PLATE XII. 
Illustrating Mr. F. W. Oliver’s paper on the Sensitive Labellum of Masdevallia 
muscosa , Rchb. f. 
Figs. 1 and 2. Front and side views respectively of a flower of Masdevallia 
muscosa. a. anther. br x . lower bract, br 1 . upper bract. /. labellum. l.p. lateral 
petal, l.s. lateral sepal, p.s. posterior sepal. In Fig. 2 the labellum is extended, 
in Fig. 1 contracted. Slightly larger than life. 
Fig. 3. Diagrammatic side view of column and extended labellum, the other 
parts of the flower being removed, a anther, bl. blade of labellum. c column. 
cr. crest, e emergence, ft. foot, h neck. r. rostellum. 
Fig. 4. Diagrammatic side view of column and contracted labellum. Position 
of lateral petals indicated at Lp. Other lettering as in Fig. 3. 
Fig. 5. View of under surface of blade. + 2. 
Fig. 6. Foot and labellum seen from above, bl. blade, cr. crest, e upper 
surface of emergence, ft. foot, h neck seen between emergence and blade. 
Fig. 7 a. Position of blade after moving through about angle of io°, to show the 
rounding of the emergence. 
