$ 
AN ENCYCLOPÆDIA 
OF HORTICULTURE. 517 
Orchid Fertilisation— continued. 
in the suitable position to reach the stigmas of the next 
plant visited. The long, narrow, spurless labellum, 
secretes honey into a groove down the middle of the 
upper surface. The insect follows up this guide as 
it climbs up the labellum, and, on reaching the upper 
end of- the groove, it is almost certain to touch the 
rostellum, and to have the pollen-masses affixed to its 
head. For a little the rostellum sinks, and closes the 
way to the stigmas; but soon it rises, leaving free access 
to the stigmas for later visitors to the flower. These 
visitors are attracted by a new supply of nectar in the 
groove. They are almost all small insects, with the 
proboscis short or absent, the nectar lying open. The 
genus Cypripedium—trepresented by C. Cal- 
ceolus, the Lady's Slipper” (see Fig. 763), 
a scarce species in England, and by many 
tropical species, e.g., C. spectabile (see Fig. 764) 
belongs to a group that possess two fertile 
stamens, situated at each side, on the lower 
surface, of a broad, shield-like plate (the re- 
presentative of the single fertile stamen in 
other Orchids). This plate overhangs the 
stigmatic surface, which lies on a prominent 
overhanging rostellum immediately below the 
plate. The labellum is much like the front 
half of a slipper (see Fig. 764). It forms a 
chamber, open above, and large enough to 
allow small bees to enter. This they do 
readily, to gnaw the hairs that line the middle 
of the floor. The lips on each side are in- 
curved, so that, when an insect wishes to 
escape by the opening, it cannot crawl out as 
it entered; nor is there room for it to fly 
out. But, at the stalk of the labellum, a small 
opening is left on each side, where, if strong 
enough, by squeezing between the labellum 
and the stigma, and then between the labellum 
and either stamen, the prisoner can escape, 
carrying away one of the pollinia. As the 
stigma is touched before the anther, the flower 
cannot be fertilised with its own pollen, but 
only with that from one previously visited. 
Few flowers are formed on each plant. 
Among exotic Orchids, the adaptations for 
fertilisation by pollen from other flowers are 
far more curious and striking even than the 
above, and the peculiarities in form and struc- 
ture of the rostellum, the pollinia, and other 
parts of the flower, are often very strange, and 
cause them to resemble insects (e.g., in the Fly 
Orchis), or a minute dove, or other objects 
too numerous to describe, or even to mention. 
Mr. Darwin has described fully some of the 
more remarkable, among which is the extremely curious 
genus Catasetum. In this genus of Orchids, the flowers 
are of different sexes, and they are so unlike that on 
C. tridentatum three supposed genera were based; the 
characters being drawn from the form of the flowers. 
These were Catasetum, based on the male; Myanthus, on 
the hermaphrodite; and Monachanthus, on the female 
flowers. The occasional presence of these flowers on 
the same plants has enabled botanists to understand 
their mutual relations. Cross-fertilisation must be 
effected before seeds can be formed; and this requires 
insect agency. In Catasetum (the male flower), the 
labellum rises up at the back of the flower (the ovary 
not making the usual half-twist), and is shaped like a 
monk’s cowl. It contains no exuded nectar, but bees 
and other insects gnaw the inner surface greedily. The 
central column projects forward below the labellum, 
and bears the anther on its upper surface, the pollinia 
and disk being embedded in the tissues till set free 
by the mechanism now to be described. From each 
side of the rostellum grows a long, slender, curved horn, 
Orchid Fertilisation—continued. 
or “antenna”; and both lie within the hollow of the 
labellum. The right antenna occupies the bottom of 
the space, with its tip just projecting beyond the left 
margin; the left one curves upwards along the back of 
the labellum. 
The slightest touch on either antenna immediately 
transmits some stimulus to the membrane over the disk 
of the pollinia, causing it to be rent; the disk springs 
out, by sudden removal of tension from the bent 
caudicle, and the whole mass is thrown forward, with 
the sticky disk in front, against the insect, if the 
antenna has been touched by an insect, and at once 
adheres in the position most likely to secure convey- 
Fic. 765. FLOWER OF CATTLEYA BICOLOR. 
ance to the stigma of the female flower. The pollinia 
are not sensitive to contact of insects with any part 
of the flower except the antennæ; but the position of 
these organs renders this contact almost certain to 
occur when the labellum is being gnawed. The female 
flowers of this species (formerly called Monachanthus 
viridis), resemble the male flowers in the position and 
general form of the labellum, which differs only in 
minor details. The column also agrees in position, but 
is smaller; the pollinia are rudimentary; the disk does 
not cohere with the pollinia, but soon falls away; and 
the antennz are absent. On the other hand, the stigmas 
and the ovaries are developed, and the seeds ripen 
abundantly. 
The form ealled Myanthus barbatus is very different 
in appearance from the other two, and Darwin points out 
that it comes near, in its structure, to the flowers of 
Catasetum callosum and of OC. saccatum, but that it is 
hermaphrodite, though not known to secd. He suggests 
that it may be a reversion to the ancestral form. Owing 
to a bend in the ovary, the column and the long-fringed 
