INTRODUCTION. 77 
An Orchid-flower properly, therefore, consists of fifteen organs 
arranged in five whorls or circles. Beginning from the outside there 
are: (1st whorl) 8 sepals; (2nd whorl) 3 petals, of which one is called 
the lip ; (8rd whorl) 38 anthers, one only of which is fertile in most 
Orchids ; (4th whorl) 8 stamens, which are undeveloped in all Orchids, 
excepting in Cypripediew, where two are fertile; (5th whorl) 3 pistils. 
In most Orchids the two suppressed stamens of the onter whorl are 
continued into the lip, and there appear as lobes, wings, calli, fringes, 
or other appendages; and this view of the nature of the lip explains its 
large size, its frequently-tripartite form, and especially the manner of 
its coherence to the column, unlike that of other petals. Of the sup- 
pressed anthers of the inner whorl, two often appear as papille, 
auricles, or tubercles (as in many of the Cape Dis and Satyria), 
while the third is absorbed into the face of the column. Of the three 
stigmas, two are usually confluent (yet often distinctly separated in the 
Cape genera, Disperis, Corycium, Pterygodium, and Ceratandra), and 
the third is modified into the rostellum. No such organ as the last- 
named exists in any other group of plants. Its function is to secrete 
viscid matter for the purpose of attaching the pollen-masses to an 
insect’s body, and, though homologically a stigma, it has lost the 
capacity of being penetrated by the pollen-tubes. ‘‘ There is every 
reason to believe that the whole of this upper stigma, and not merely 
a part, has been converted into the rostellum ; for there are plenty of 
cases of two stigmas, but not one of three stigmatic surfaces being 
present in those Orchids which have a rostellum. On the other hand, 
in Cypripedium and Apostasia, which are destitute of a rostellum, the 
stigmatic surface is trifid’’ (ib. p. 248). 
In concluding this portion of his subject Darwin observes :—-‘‘ It is 
interesting to look at one of the magnificent exotic species, or indeed 
at one of our humblest forms, and observe how profoundly it has been 
modified, as compared with all ordinary flowers,—with its great 
labellum, formed of one petal and two petaloid stamens,—with its 
singular pollen-masses, hereafter to be referred to,—with its column 
formed of seven cohering organs, of which three alone perform their 
proper function, namely, one anther and two generally confluent 
stigmas,—with the third stigma modified into the rostellum and 
incapable of being fertilised,—and with three of the anthers no longer 
functionally active, but serving either to protect the pollen of the 
fertile anther, or to strengthen the column, or existing as mere 
rudiments, or entirely suppressed. What an amount of modification, 
cohesion, abortion, and change of function do we here see! Yet, 
hidden in that column, with its surrounding petals and sepals, we know 
- that there are fifteen groups of vessels, arranged three within three, in 
alternate order, which probably have been preserved to the present 
B 2 
