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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    stinct, the origin of the ovulum from one only of these cords is satisfactorily shown. An ovarium with two or a greater number of cells, whose placentfe project into the cavities more or less from their inner angles, is an organ, the composition of which is suffi- ciently obvious. But a compound ovarium may be differently constructed; and, first, instead of each simple organ forming a complete cell by the union of its own margins or adjoining portions of its surface, the corresponding margins or adjoining portions of surface of the proximate component parts may unite to- gether so as to form a parietal placenta, often apparently simple, but in reality double in all cases. This view of the composition of a unilocular ovarium having two or more parietal placentae is also very generally received. But ex- ceptions, supposed to prevail in w'hole families, in which the disc and not the margins are placentiferous, have lately been assumed by Professor Lindley, Orchidece and Orobanchece being the examples of this structure to which he more par- ticularly refers. The accurate determination of this question appears to me of great importance to the theoretical botanist, but the subject will be most advantageously discussed after treating of the origin and modifications of stigmata. An ovarium less manifestly compound is that in which the centre of the cavity is occupied by a placenta entirely uncon- nected with its sides; the supposed inflected portions of each component organ, according to the view here adopted, being removed, or reabsorbed so completely in a very early stage of its development as to leave no trace of their existence either on the walls of the cavity or on the surface of the central placenta, which may either be polyspermous, or produce only a smaller and definite number of ovula having a relation to its supposed component parts, or, lastly, in some cases be re- duced to a single ovulum. These are the principal modifications of the compound ova- rium when forming a simple series; but it is necessary to ob- serve that both surfaces of the inflected and included portions of the carpels are not unfrequently equally productive of ovula, a structure which is manifest in many Cyriandracece, especially Cyriandra, although in several other genera of the same family the production is confined to the inner or upper surface of the margin. In other cases the polyspermous ovu- liferous portion or placenta is connected with the inner angle of the cell by a single point only, which may proceed either from the apex or base of the cavity. This modification of