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 506 ON THE ORGANS AND MODE OF FECUNDATION

ovula, are of a texture somewliat different from that of the greater part of the cavity, but still more obviously different from that of the cavity of the style, being neither apparently 704] secreting nor consisting of similar utriculi. A narrow line of like surface is found extending on each side of every placenta nearly as far as it is ovuliferous. The three lines occupying the upper part of the axes, and the six lines marginal to the three placentae, may, for a reason which will hereafter appear, be called the conducting surfaces of the ovarium.

The female organ, as now described, is in a proper state to be acted upon by the pollen applied to the stigma, and for the transmission of the fecundating matter into the cavity of the ovarium, in a manner and form which I shall presently attempt to explain.

In reflectino' on the whole evidence existinsr in favour of the direct application of the pollen mass to the stigma, and especially on the recent experiments of Professor Trevi- ranus,-^ I could no lonojer doubt that in this manner im- pregnation Avas actually effected in Orchideae ; and the sole difficulty in my mind to its being the only way arose from adverting to a circumstance that must have been remarked by every one who has particularly attended to this family, either in Europe or in tropical regions; namely, that all the capsules of a dense spike are not unfrequently ripened : a fact which at first seems hardly reconcilable with this mode of fecundation, at least on the supposition that the pollen mass is applied to the stigma by insects.

Without going fully into the question at present, I shall here only remark, that in several such cases I have satisfied myself, by actual examination of the stigmata belonging to capsules taken at many different heights in the spike, that pollen, by whatever means, had actually been applied to them.^

1 ZeHscJmfif. ThjsioL \\ p. 225.

^ It may also be observed, that the same difficulty applies to many otlier cases of dense inflorescence, as to the female spikes or strobili of Couiferse, Zamia, and Zea; in all of which the symmetry of the ripe fruit is generally perfect, although partial failures of impregnation might be at least equally expected.

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