"For the due fertilization of the common _Barberry_, it is necessary that its irritable stamens should be brought into contact with the pistil, by the application of some stimulus to the base of the filament; but this would never take place were not insects attracted, by the melliferous glands of the flower, to insinuate themselves amongst the filaments, and thus, while seeking their own food, unknowingly to fulfil the intentions of Nature in another department." _In some cases the agency of the hive-bee is inadequate to produce the required end; in these the humble-bee is the operator:_ these alone, as Sprengel has observed, are strong enough for instance, to force their way beneath the style-flag of the _Iris Xiphium_, which in consequence is often barren. _Other insects besides bees are instrumental in producing the same ends;_ indeed they are necessary instruments: and hence according to the same naturalist, in some places, where the particular insect required is not to be met with, no fruit is formed upon the plant which is usually visited by it, where it is indigenous; for he supposes that _some plants have particular insects appropriated to them_. The American _Aristolochia Sipho_, though it flowers plentifully, never forms fruit in our gardens, probably for the reason just assigned. The _Date Palm_ affords a striking instance of the necessity of extraneous intervention to perfect fructification; male and female flowers are borne on separate trees, and unless the two sorts be in the neighbourhood of each other, the fruit has no kernel and is not proper for food. There was a tree of this kind, bearing female flowers, at Berlin, for the fructification of which, a branch, with male flowers upon it, was once sent by post from Leipsic, (20 German miles,) and being suspended over some of the pistils, the tree afterwards yielded fruit and seed in abundance. +Professor Willdenow+ has stated a very curious circumstance, concerning the _Aristolochia Clematitis_. He observes that the stamens and pistils of the flower are inclosed in its globular base, the anthers being under the stigma, which thereby requires the intervention of an insect, to convey the pollen to it. The _Tipula pennicornis_ accomplishes this object; it enters the flower by its tubular part, which is thickly lined with inflected hairs, so as readily to admit the fly, but totally to prevent its release, till by the fading of the corolla the hairs have fallen flat against its sides. Hence the insect in struggling to effect its escape, brushes off the pollen and applies it to the stigma, thereby accomplishing the fertilization of the flower. INDEX.