OBSERVATIONS ON THE FERTILIZATION OF DISA MACRANTHA. 45 
effected by some of the small bees or beetles which frequent 
flowers. 
The position of the two viscid disks (which are so prominently 
situated, and which have their upper surface viscid, instead of the 
under surface as is usually the case in Orchids) shows plainly their 
office as steps to the forum of the galeatic chamber, one to each 
receptacle. 
This is the only instance that I know of amongst Orchides» in 
which the adaptation suggests that the tarsi of insects are the 
agents of fertilization, although in Asclepiads this would appear 
to be in some instances the normal method. 
e | 
Some Observations on the Fertilization of Disa macrantha. By 
By J. P. Mansit Weate, B.A. Oxon. (Communicated by 
C. Darwin, Esq., F.R. & L.SS.) 
[Read November 23, 1870.] 
TuE diminution in size and simplicity of structure of the la- 
bellum in some species of the genus Disa would seem to indi- 
cate its little service as an attractor of insects and as a necessary 
appendage to the fertilization of the flowers, its office being re- 
placed by the large and often gaily-coloured posterior sepal. 
In the adjoining genus Brownleea, this reduction is so con- 
siderable, that it may be said to be in a merely rudimentary con- 
dition, and to have altogether lost the important function it 
usually holds in the order. Compared with some species of Disa, 
it is comparatively large in D. macrantha ; certainly it is in rela- 
tive proportions to D. grandiflora. 
The back spurred sepalis, on the other' hand, proportionally 
large. 
The two lateral sepals, the petals, and labellum spread out- 
wardly from the column, so as to form a salver-like opening to 
the funnel-shaped posterior sepal. 
The colour of the blossom varies much, from nearly pure white 
with a few pale mauve spots on the petals and labellum, to a 
bright rich purple; sometimes the spots are small and indistinct, 
sometimes in large blotches, scarlet and almost orange. 
It emits, especially towards night, an overpowering, heavy 
perfume, almost too strong to be agreeable. 
