On the relative position of the divisions of stigma and parietal placentae in the compound ovarium of plants / by Robert Brown.

  • Robert Brown
Date:
[1840]
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Licence: Public Domain Mark

Credit: On the relative position of the divisions of stigma and parietal placentae in the compound ovarium of plants / by Robert Brown. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    in Orchidece each apparent stigma is formed by the conflu- ence of the two stigmata of one and the same carpel, is proved by tracing to their origins their vascuhir cords, which are found to coalesce with those of the three outer foliola of the perianthium. This view of the composition of the ovarium in OrchidecB is confirmed by finding that it agrees with the ordinary ar- rangement in nionocotyledonous plants; namely, the op])osi- tion of the double parietal placentae to the three inner divi- sions of perianthium *, while in Apostasia the three placentae of the trilocular ovarium are opposite to the three outer divi- sions ; and it is further strengthened on considering what takes place m Scitaminece,\s{\evet\\Q same agreement is found botli in the placenta of the trilocular ovarium, which in this family is the ordinary structure, and in the unilocular, which is the exception. I am aware that the agreement of Orchidece with the usual relation of parts in Monocotyledones is not admitted by M. Achilla Richard, nor by Mr. Lindley, who has adopted his hy- pothesis respecting the structure of the flower in this family. According to M. Richard, the outer series of perianthium is ge- nerally wanting, being found only in one genus, Epistephium: the three outer divisions actually existing in the whole order, according to this view, become petals, and the three inner di- visions sterile petaloid stamina. I have some years agof stated several objections to this hypothesis; at present 1 shall advert to one of those only, considering it as conclusive ; namely, the position of the two lateral stamina, which are generally rudimentary, but in some cases perfectly developed, in this family. In several species of Cyjyripedium, which is one of these cases of perfect deve- lopment, I had then ascertained, by means of numerous trans- verse sections made at various heights in the column and at its base, that their vascular cords united with those of the two lateral inner divisions of the flower, while that of the third, generally the only perfect stamen, is manifestly opposite to the anterior division of the outer series. The position of sta- mina, therefore, so far from being regular, as the hypothesis in question considers it, is absolutely without example, two of the inner series being opposite to two of the supposed outer series of stamina. A very different view respecting the formation of the ova- rium in Orchidece is that first advanced by Mr. Bauer and • Denhara, Trav. in Afr. Append, p. 243. t Liiiu. Soc. Tians. vol. xvi. p. 098.