538 ON THE ORGANS AND MODE OF FECUNDATION
My first observation on Bonatea related to the probability of a single insect impregnating several or even many flowers with one and the same mass of pollen.
To efl'ect this, it is only necessary that the viscidity of the retinaculum or gland with w^hich the pollen mass becomes inseparably connected, and by means of which the mass is removed from its cell and adheres to the insect, should exceed that of the surface of the stigma, and that the viscidity of the stigma should be sufficient to overcome the mutual cohesion of the lobules composing the mass.
These different degrees of viscidity are very manifest in Bonatea sjieciosa, in which, imitating the supposed action of the insect, I have succeeded in impregnating most of the flow^ers of the spike with a single pollen mass. I beheve they exist also in the greater number of Ophrydese, as well as in many Neotteae and Arethuseae.
Bat even in Ophrydeae they are not universally met with, a very remarkable exception existing, I believe, in the wdiole genus Ophrys, in which the resemblance of the flower to an insect is so striking, and in which also the retinacula, w^hose viscidity hardly equals that of the stigma, are included and protected by concave processes of the upper lip of that organ.
It may also be remarked, that in the genus Ophrys im- pregnation is frequently accomplished without the aid of insects, and in general the whole pollen mass is found adhering to the impregnated stigma. Hence it may be conjectured, that the remarkable forms of the flowers in this genus are intended to deter not to attract insects, 7ii] whose assistance seems to be unnecessary, and the action of w4iich, from the diminished vicidity of the retinaculum, might be injurious. On this subject I will also hazard another remark, that the insect forms in Orchideous flowers, resemble those of the insects belonging to the native country of the plants.
The next object I had in view was to determine the flrst appearance and progress of the mucous tubes.
My observations on the origin of these tubes are not altoo'ether satisfactory.
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