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68 compel moths to insert their proboscides symmetrically into the nectary, and there would be no advantage in their doing so.

Gymnadenia albida.—The structure of the flower of this species resembles in most respects that of the last; but, owing to the upturning of the labellum, it is rendered almost tubular. The naked elongated discs are minute and approximate. The stigmatic surfaces are partially lateral and divergent. The nectary is short, and full of nectar. Small as the flowers are, they seem highly attractive to insects: of the eighteen lower flowers on one spike, ten had both, and seven had one pollinium removed; on some older spikes all the pollinia had been removed, except from two or three of the uppermost flowers.

Gymnadenia odoratissima is an inhabitant of the Alps, and is said by Dr. H. Müller to resemble in all the above characters G. conopsea. As the flowers, which are pale coloured and highly perfumed, are not visited by butterflies, he believes that they are fertilised exclusively by moths. The North American G. tridentata, described by Professor Asa Gray, differs in an important manner from the foregoing species. The anther opens in the bud, and the pollen-grains, which in the British species are tied together by very weak threads, are here much more incoherent, and some invariably fall on the two stigmas and on the naked cellular tip of the rostellum; and this latter part, strange to say, is penetrated by the pollen-tubes. The flowers are thus self-fertilised. Nevertheless, as Professor Gray adds, "all the arrangements for the removal