STIGMA AND PARIETAL PLACENTA IN PLANTS. 5G1
divisions; and it is further strengthened on considering what takes place in Scilaniincce, where the same agreement is found both in the pkicenta3 of the trilocular ovarium, which in this family is the ordinary structure, and in the unilocular, which is the excej)tion.
I am aware that the agreement of Orc/ildcce with the [in usual relation of parts in Monocotyledones is not admitted by M. Achille llichard, nor by Mr. Lindloy, who has adopted his hypothesis respecting the structure of the flower in this family. According to M. Richard, the outer series of perianthium is generally wanting, being found only in one genns, Epistephium: the three outer divisions actually exist- ing in the whole order, according to this view, become petals, and the three inner divisions sterile petaloid stann'na.
I have some years ago^ stated several objections to this hypothesis; at present I 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 Cyprip)edium , which is one of these cases of perfect deve- lopment, I had then ascertained, by means of numerous transverse sections made at various heights in the colunm 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 stamina, therefore, so far from being regular, as the hypothesis in question considers it, is absolutely without example, tw^o of the inner series being opposite to two of the supposed outer series of stamina.
A very dificrent view respecting the formation of the ovarium in Orchidece is that first advanced by Mr. Ikuicr and adopted by Mr. Lindley, namely, that it consists of six carpels, of which three, placed opposite to the outer series of perianthium or sepals, are sterile; the remaining three, opposite to the imier series, or petals, being fertile, and bearing their placentae on their axes or disks.
The chief argument in support of this view is no doubt ' Liun. Soc. Trans, vol. xvi, p. C9S. {Afi/c, p. 5()L)
- 5G
�� �
