Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/65

 The flower stands with the labellum uppermost, that is in a reversed position compared with most Orchids. The labellum forms a helmet or bucket, with the distal portion represented by three minute points. It is clear from this position that the labellum cannot hold nectar; but its walls are thick, and have, as in the other species, a pleasant nutritious taste. The stigmatic chamber, though functionless as a stigma, is of large size. The summit of the column, and the spike-like anther, are not so much elongated as in C. saccatum. In other respects there is no important difference. The antenine are of greater length; their tips for about one-twentieth of their length are roughened by cells produced into papillæ.

The pedicel of the pollinium is articulated as before by a hinge to the disc; the anterior end of the disc is upturned, so that, when attached to an insect's head, the pedicel cannot move backwards, only forwards, a movement which apparently comes into play in the fertilisation of the female plant. The disc is, as in the other species, of large size, and its posterior end, which during ejection first strikes any object, is much more viscid than the rest of the surface. This latter surface is drenched with a milky fluid, which rapidly turns brown when exposed to the air, and sets into a cheesy consistence. The upper surface of the disc consists of strong membrane formed of polygonal cells, each containing one or several balls of brown translucent matter. This membrane rests on, and adheres to, a thick cushion, formed of rounded balls of brown matter (which lower down in the cushion become extremely irregular in shape) separated from each other and embedded in transparent, structureless, highly elastic matter. This cushion towards the posterior end of the disc passes into the extremely viscid matter. This latter matter when consolidated is brown, translucent, and homogenous. Altogether the disc presents a much more complex structure than in the other Vandeæ.

I need not further describe this species, excepting the position of the antenine. They occupied exactly the same position in the six flowers examined. They do not stand symmetrically. They are both sensitive,—whether in an equal degree I will not say. They both lie curled within the bucket-like labellum; the left-hand one stands higher up, with its inwardly bowed extremity in the middle; the right-hand antenna lies lower down and crosses the whole base of the labellum, with its tip just projecting beyond the left margin of the base of the column. From the position of the petals and sepals, an insect visiting the flower would almost certainly alight on the crest of the labellum; but it could hardly gnaw any part of the great cavity of the labellum without touching one of the two antennae, for the left-hand one guards the upper part, and the right-hand one the lower part: and when these are touched the pollinium will infallibly be ejected and strike the head or thorax of the insect.

The position of the antennæ in this Catasetum may be compared with that of a man with his left hand raised and bent so that his hand stands in front of his chest, and with his right arm crossed lower down so that the fingers project just beyond his left side. In Catasetum callosum both arms are held lower down, and are extended symmetrically. In C. saccatum the left arm is bowed and held in front, as in the C. tridentatum, but rather lower down; whilst the right arm hangs down almost paralysed, with the hand turned a little outwards. In every case notice will be given in an admirably manner, when an insect visits the labellum, and the time has at last arrived for the ejection of the pollinium and for its transportal to the female plant.

Catasetum tridentatum is interesting under another point of view. Botanists were astonished when Sir Robert Schomburgk stated that he had seen three forms, believed to constitute three distinct genera, namely, Catasetum tridentatum, Monachanthus viridis, and Myanthus barbatus, all growing on the same plant. Lindley remarked that "such cases shake to the foundation all our ideas of the stability of genera and species." Sir. R. Schomburgk affirms that he has seen hundreds of plants of C. tridentatum in Essequibo without ever finding one specimen with seeds, but that he was surprised at the gigantic seed vessels of the Monachanthus; and he correctly remarks that "here we have traces of sexual difference in Orchideous flowers."