420 -~ Transactions.— Botany. 
of the rostellum become converted into & milky and excessively viscid 
substance, while the whole surface of the stigma secretes abundantly a 
clear, viscid matter, and a drop of sweet fluid is secreted at the base of 
the column. 
The action of the parts is exceedingly simple. An insect alighting on 
the labellum weighs it down very easily, and thus gains access to the nectar 
at its base. The elasticity of the labellum, however, tends to keep it press- 
ing against the column, and thus compels the insect to brush against the 
viscid rostellum. The pollinia are very easily withdrawn by an upward 
movement, as can be seen by introducing a needle or pencil point, and 
touching the rostellum in withdrawing it, when one or more of the pollinia 
will be withdrawn with it. The lateral lobes of the labellum and the guiding 
ridges on its surface would prevent an insect reaching the nectar without 
touching the rostellum when leaving the flower; and any insect entering 
another flower with pollinia on its head, could not fail to leave these on the 
stigma. By inserting a fly, this action was easily seen, all four pollinia 
` being withdrawn, with their eaudicle glued over the insect's right eye. Out 
of twenty-two flowers examined, only five had their pollinia removed from 
the anther cases, but as the plant was growing on a veranda away from 
its native habitat, this was no criterion. I regret that I did not fertilize 
any of the flowers on this plant with their own pollen. Those fertilized by 
pollen from other flowers on the same plant produced fine capsules. 
Tribe ARETHUSEA. 
(8.) Corysanthes macrantha. 
Both this species and C. rivularis were examined by me, but the flowers 
are almost identical in structure, the difference not affecting the relations of 
the parts. They are very striking in appearance, owing to their lurid 
purple colour, and the long twisted sepals and petals, which give them an 
extraordinary resemblance to a large spider sitting on a leaf. The upper 
sepal is large, prominent, and helmet-shaped, and projects forward over the 
flower. The labellum is large and involute, almost semi-cylindrical, with 
its external margin fimbriated and expanded downwards into a longish tip. 
It is not attached continuously at its base. On each side of the flower, 
when in bud, a small slit is seen, which widens by an expansion of the 
margin (which is thus caused to arch slightly outwards) into a small circular 
aperture. By the contact of the in-turned edges of the labellum, and the 
overlapping of the upper sepal, a horizontal aperture is left in the mouth of 
the flower, which bends at right-angles a little way in, and opens into a 
tolerably large cavity. Placed quite at the bottom of this is the short, 
thick column, lying almost horizontally in C. rivularis, and somewhat more 
erect in C, macrantha, The stigmatic cavity is deep, and on its posterior 
