238 Oliver . — On the Sensitive Labellum 
mentioned by Hooker 1 , and described in more detail by Fitz- 
gerald 2 ; here the labellum is irritable to contact, a light touch 
at its free end causing the narrowed hinge hastily to contract, 
so that the labellum is raised and forms, together with the 
column and lateral petals, an almost closed box. 
Hence it would appear that so far only two genuine cases of 
motile labellums have been recorded ; Megaclinium , in which 
the movement is spontaneous, and Pterostylis , where it is 
called forth by an external stimulus. The object of the pre- 
sent paper is to give an account of the mechanism of move- 
ment of a new case, Masdevallia muscosa , Rchb. f. 
Originally described by Reichenbach 3 , from dried specimens 
collected in New Granada by Shuttlewortli, it was only in May 
of this year (1887) — when a plant of it flowered in the Kew 
orchid-house— that the motility of the labellum of this species 
was discovered. This discovery is due to Mr. W. Bean, fore- 
man of that house, and has been put on record in a recent 
number of the Gardeners’ Chronicle 4 . Through the kindness 
of the Director of the Royal Gardens, and of Mr. Watson, 
I have been enabled to investigate this interesting phenome- 
non. I wish also to take this opportunity of acknowledg- 
ing the help so freely rendered by Mr. Watson in connection 
with this and many other matters. The plant flowered a 
second time — five months later — so that I have been able to 
confirm and add to my earlier results. 
Masdevallia muscosa produces a number of flowers borne 
singly on erect scapes some 15 cm. long. Figures 1 and 2, PL 
XII, show front and side views respectively of a single flower, 
slightly enlarged. The scapes are clothed with a dense cover- 
ing of stiff glandular emergences — a most uncommon feature 
in Masdevallia. On the scape are inserted two sheathing 
scaly bracteoles (Fig. 2, bP and br 2 ), one about | up, the other 
at the insertion of the flower. The ovary, covered with 
1 J. D. Hooker, Flora of Tasmania, vol. ii. p. 18. 
2 Fitzgerald, Australian Orchids, Sydney, 1882. 
3 Gard. Chron. Apr. io, 1875. 
i Gard. Chron. June 25, 1887. 
