This anomaly is so far of importance, as it throws some doubt on the view which I have taken of the labellum being always an organ compounded of one petal and two petalold stamens; for if any one were to assume that from some unknown cause the lateral vessels of the lower petal in an early progenitor of the Orchidean order had wandered from their proper course into the antero-lateral ovarian groups, and that this structure had been inherited by all existing Orchids, even by those with the smallest and simplest labellums, I could answer only as follows; but the answer is, I think, satisfactory. From the analogy of other monocotyledonous plants, we might expect the hidden presence of fifteen organs in the flowers of Orchids, arranged alternately in five whorls; and in Orchid-flowers we do find fifteen groups of vessels exactly thus arranged. Hence there is a strong probability that the vessels, A 2 and A 3, which enter the sides of the labellum, not in one or two cases, but in all Orchids seen by me, and which occupy the precise position which they would have occupied had they supplied two normal stamens, do really represent modified and petalold stamens, and are not lateral vessels of the lower petal which have wandered from their proper course.
In Habenaria and Bonatea,[1] on the other hand, the vessels from the sides of the upper sepal and of the two upper petals, which enter the wrong ovarian groups, cannot possibly represent any now lost and once distinct organs.
We have now finished with the general homologies of the flowers of Orchids. 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 usually great labellum, formed of one petal and two petalold stamens, with its singular pollen-masses, presently 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 incapable of fertilisation and modified into the wonderful rostellum,—with three of the anthers no longer capable of producing pollen, 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, change of function, cohesion, and abortion 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 alternating order, which probably have been preserved to the present time from having been developed in each flower at a very early period of growth, before the shape or existance of this or that part signified to the well-being of the plant.
Can we, in truth, feel satisfied by saying that each Orchid was created, exactly as we now see it, on a certain "ideal type;" that the Omnipotent Creator, having fixed on one plan for the whole Order, did not please to depart from this plan; that He, therefore, made the same organ to perform diverse functions—often of trifling importance compared with their proper function—converted other organs into mere purposeless rudiments, and arranged all as if they had to stand separate, and then made them cohere? Is it not a more simple and intelligible view that all Orchids owe what they have in common to descent from some monocotyledonous plant, which, like so many other plants of the same division, possessed fifteen organs, arranged alternately three within three in five whorls; and that the now wonderfully changed structure of the flower is due to a long course of slow modification,—each modification having been preserved which was useful to each plant, during the incessant changes to which the organic and the inorganic world has been exposed?
On the gradation of Organs
The rostellum, the pollinia, the labellum, and, in a lesser degree, the column, are the most remarkable points in the structure of Orchids. Of the two latter parts enough has been already said. No organ like the rostellum exists in any other flower. If the homologies in Orchids had not been pretty well known, those who believe in the separate creation of each being might have advanced this as a case of a perfectly new organ specially created, and which could not have been developed by successive slow modifications of any pre-existing part.
- ↑ In Bonatea speciosa, of which I have examined only dry specimens sent me by Dr. Hooker, the vessels from the sides of the upper sepal enter the postero-lateral ovarian group, exactly as in Habenaria. The two upper petals are divided down to their bases, and the vessels supplying the anterior segment and those supplying the anterior portion of the posterior segment unite and then run, as in Habenaria, into the antero-lateral (and therefore wrong) groups. The anterior segments of the two upper petals cohere with the labellum, making it, in a most unusual manner, five-segmented. The two wonderfully protuberant stigmas also cohere to the upper surface of the labellum; and the lower sepals apparently also cohere to its under side. Consequently a section of the base of the labellum divides one lower petal, two petalold anthers, portions of the two upper petals, and apparently of the two lower sepals and the two stigmas: altogether the section passes through the whole of or through portions of no less than seven or nine organs. The base of the labellum is here as complex an organ as the column of other Orchids.
