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 IX ORCHIDE^ AND ASCLEPIADEiE. 517

viscid substance liangs to them, which, when higlilv magnified, appears to consist of very slender tubes con- taining minute globules ; and these tubes with their con- tents he considers as constituting the early preparation for the formation of pollen. He also asserts that the tops of the styles are not originally connected with the pentagonal body to which the glands belong — the stigma of Adanson, Jacquin, and others ; and that therefore the true stigmata are those extremities of the styles on which, he adds, vesicles and threads are observable. And lastly, he sup- poses that impregnation, which he says is of rare oc- currence in this fiunily, does not usually take place until those stigmata have penetrated through the substance of the pentagonal body, and are on a level with its apex ; at the same time he is disposed to believe that insects may occasionally assist in this function, by carrying the fecun- dating matter directly to the stigmata, if I understand him, even before they enter the pentagonal body. His con- clusion therefore is, that in Asclepiadeae impregnation may be effected in two different ways.

This description, in several respects so paradoxical, and of which Jacquin has overlooked some of the most im- portant parts, is too remarkable to be here either omitted or abridged. It is not indeed strictly correct in more than two points, namely, in the pollen masses being originally distinct from the glands, and in the masses, when found implanted in the membrane surrounding the ovarium, having minute tubes filled with granular matter :7i7 hanging to them. The remaining statements, however, though essentially erroneous, are so far founded in fjict, that had Gleichen either opened or rather dilated the opening which must have existed in the pollen mass when these tubes were found hanging to it, and more carefully attended to the state of the other parts of the flower wheft the mass was seen implanted in the tube, he must neces- sarily have obtained a correct view of the whole structure, and consequently have greatly advanced — by at least half a century — not only our knowledge of this particular family, but also the general subject of vegetable impregnation.

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