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124 tion of the pollinia, so here the rostellum moves backwards, and not only recovers its former arched position, but stands upright, leaving the stigmatic surface, now rendered more adhesive, perfectly free for pollen to be left on it. The pollen-masses, when once cemented to an insect's forehead, will remain attached to it, until they are brought into contact with the stigma of a mature flower; and then these encumbrances will be removed, by the rupturing of the weak elastic threads which tie the grains together; the flower being at the same time fertilised.

Listera cordata.—Professor Dickie of Aberdeen was so kind as to send me, but rather too late in the season, two sets of specimens. The flowers have essentially the same structure as in the last species. The loculi of the rostellum are very distinct. Two or three little hairy points project from the middle of the crest of the rostellum; but I do not know whether these have any functional importance. The labellum has two basal lobes (of which vestiges may be seen in L. ovata) which curve up on each side; and these would compel an insect to approach the rostellum straight in front. In two of the flowers the pollinia were firmly cemented to the crest of the rostellum; but in almost all the others the pollinia had been previously removed by insects.

In the following year Professor Dickie observed the flowers on living plants, and he informs me that, when the pollen is mature, the crest of the rostellum is directed towards the labellum, and that, as soon as touched, the viscid matter explodes, the pollinia becoming attached to the touching object; after the explosion, the rostellum bends downwards, thus protecting the virgin stigmatic surface; subsequently it rises up and exposes the stigma; so that here everything goes on