Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/73

From information given me by Mr. Veitch it appears that, when the end of the column is touched, some movement takes place; and, from the analogy of Catasetum, it is probable that the protuberances on the margin of the stigmatic chamber are sensitive. These protuberances may be provisionally considered as nascent antenine. It is obvious, from the section given, that the disc, as long as its viscid surface rests against the roof of the stigmatic chamber, cannot adhere to any object; but Mr. Veitch informs me that, when he has touched the end of the column, the disc has adhered to his fingers. These facts perhaps suffice to show what takes place under nature. A large insect visits the thick and fleshy labellum, which is overarched by the column, and touches with its back the sensitive and protuberant edges of the stigmatic chamber: when thus excited the disc alone is flirted out and adheres to the insect's back; the insect flies away, drags the pollen-masses from under the anther, and carries them to another flower. The insect, standing in the same position, inserts the pollen-masses into the stigmatic chamber, and the flower is fertilised.

When I received the flowers of this second species of Mormodes and of Cycnoches, I did not examine their ovaria and stigmas, for I knew nothing at that time about the sexual forms of Catasetum. Mormodes ignea is an hermaphrodite; if the second species is an hermaphrodite, it cannot be fertilised, owing to the size of the curtain of the disc, until its own pollinium has been removed. With respect to Cycnoches, it is known, from an account published by Lindley,^[1] that C. ventricosum produces on the same scape flowers with a simple labellum, others with a much segmented labellum, and others in an intermediate condition. From the analogous differences in the labellum of the sexes in Catasetum, we may believe that we here see the male, female, and hermaphrodite forms of Cycnoches.

Of Lindley's fourth and sixth Tribes, viz. The Ophrea and Neottee, plenty of British forms have been described. Of the fifth Tribe, the Arethusee, I have not seen any living flowers. Judging from statements with respect to three distantly allied forms in this tribe, mechanical aid is requisite for their fertilisation. Irmisch makes this remark with respect to Epipogium aphyllum.^[2] Mr. Rodgers, of Sevenoaks, informs me that in his hot-house species of Limodorum did not set their fruit without aid; and this is likewise well known to be the case with the Vanilla. This latter genus is cultivated for its aromatic pods in Tahiti, Bourbon, and the East Indies; but does not fruit without artificial aid.^[3] This fact shows that some insect in its own American home is specially adapted for its fertilisation; and that the insects of the above-named tropical

1. 'Vegetable Kingdom,' 1853, p. 177. Lindley has also published in the 'Botanical Register,' fol. 1951, a similar case of the production of two forms on the scape in another species of Cycnoches.
2. 'Beiträge zur Biologie der Orchideen,' 1853, s. 55.
3. For Bourbon see 'Bull. Soc. Bot. de France,' tom. i. 1854, p. 290. For Tahiti see H. A. Tilley, 'Japan, the Amour, etc.,'1861, p. 375. For the East Indies see Morren in Annals and Mag. of Nat. Hist., 1839, vol. iii. p. 6.