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

  • Brown, Robert, 1773-1858.
Date:
[1840]
Catalogue details

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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    pound but unilocular ovariuni, m hile the placentae of the ad- ioinincr carpels are united, the stigmata of each carpel are generally confluent. But this rule admits of exceptions, as in Parnassia, in many Crucifera, and in Papaveracea: in all these cases the stigmata as well as placentae of the adjoining carpels are confluent, a structure satisfactorily proved in Cru- c'lferce by several cases of monstrosity, in which the stamina are transformed into pistilla; and in Papaveracem by a series of modifications of structure as well as by a like transforma- tion of stamina. A similar confluence of stigmata in the compound multi- locular pericarpium is of much rarer occurrence; it is found, however, in the majority of Iridece, in which the three stig- mata alternate with the cells, and consequently with the pla- centcE of the trilocular ovarium. That this is tbe correct view of the composition of the stigmata in Iridea is at least probable from their occasional deep division, and more parti- cularly still from the bifid petal-like styles or stigmata which are opposite to the cells of the ovarium in other genera of the same family, as in Iris and Moraa. In both these arrange- ments the adaptation to the performance of function is equally manifest. If the correctness of these observations be admitted, it fol- lows that characters dependent on the various modifications of stigmata are of less value, both in a systematic point of view as determining the limits of families, and theoretically in ascertaining the true composition of organs, than those de- rived from the analogous differences in the ovariaor placentae. In those cases in which the nature of the composition of the ovarium is doubtful, it may, in the first place, be remarked, that wherever in the compound unilocular pistillum the pla- centae are double or two-lobed, it is more probable that such placentae are derived from two adjoining carpels, and are con- sequently marginal or submarginal, than that they occupy the disc of one and the same carpel: this being entirely the ap- pearance in many cases where the marginal origin of placentae is admitted; while in the greater part of those in which the disc is known to be ovuliferous, the ovula are never collected in two distinct masses, being generally scattered equally over the surface. But the double placentae are manifest in Orchidem, the prin- cipal family in which Mr. Lindley considers the ovula as oc- cupying the disc and not the margins. In this family also the alternation of stigmata with placentae is that relation which is most usual in compound unilocular ovaria, where the ap- parent number of stigmata and placentaj is equal; and that