Note 74 — IDEAS FOR A PHYSIOGNOMY OF PLANTS.
Henry G. (Henry George) Bohn translation
p. 211—“Winged Insects.”
The fructification of diœcious plants was at one time principally ascribed to the agency of the wind. It has been shown by Kölreuter, and also with much ingenuity by Sprengel, that bees, wasps and numerous small winged insects, are the main agents in this process. I use the phrase “main agents”, since I cannot regard it as consonant to nature that fructification should be impossible without the intervention of these insects, as Willdenow has also fully shewn.[KA] On the other hand dichogamy, sap-marks, (maculæ indicantes), coloured spots indicating the presence of honey-vessels, and fructification by insects, appear to be almost inseparable from one another.[KB]
The statement often repeated since Spallanzani, that the diœcious common hemp (Cannabis sativa), which was introduced into Europe from Persia, bears ripe seeds without being in the neighbourhood of pollen-tubes, has been entirely refuted by more recent investigations. When seeds have been obtained, anthers in a rudimentary state have been found near the ovarium, and these may have been capable of yielding 245some grains of fructifying pollen. Such hermaphrodism is frequent in the whole family of Urticeæ, but a singular and hitherto unexplained phenomenon is manifested in the forcing-houses at Kew by a small New Holland shrub, the Cœlebogyne of Smith. This phanerogamic plant brings forth seeds in England without exhibiting any trace of male organs, and without the bastard introduction of the pollen of any other plant. “A species of Euphorbiaceæ,” (?) writes the distinguished botanist, Jussieu, “the Cœlebogyne, which, although but recently described, has been cultivated for many years in English conservatories, has several times borne seeds, which were evidently perfect, since the well-formed embryos they contained have produced similar plants. The most careful observations have hitherto failed in discovering the slightest trace of anthers or even pollen in the flowers, which are diœcious. No male plants of this kind are known to exist in England. The embryo cannot therefore have come from the pollen, which is wholly deficient, but must have been formed entirely in the ovule.”[KC]
In order to obtain a fresh and confirmatory explanation of this important and isolated physiological phenomenon, I lately addressed myself to my young friend, Dr. Joseph Hooker, who after having accompanied Sir James Ross in his Antarctic voyage, has now joined the great Thibeto-Himalayan expedition. Dr. Hooker wrote to me as follows from Alexandria, at the close of December, 1847, prior to his embarkation at Suez: “Our Cœlebogyne still flowers with my father at Kew, as well as in the Gardens of the Horticultural Society. It ripens its seeds regularly. I have repeatedly examined it with care, but have never been able to discover a penetration of pollen utricles into the stigma, nor any traces of their presence in the latter or in the style. In my herbarium the male blossoms are in small catkins.”