STIC^rA AND PARIETAL PLACKNT.^ IN PLANTS. 557
manifest in a monstrosity of Tropceolnm wnjiis, \w \\\\vA\ the stamina arc converted into pistilhi; l)nt the complete action beiiio^ impeded by the presence of the regnlar trilocular pistillnm, and the two mari^inal cords of each open ovarium remaining distinct, the origin of the ovulum from one only of tliese cords is satisfactorily shown.
An ovarium with two or a greater number of cells, whose placenta3 ])roject 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 together 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 exceptions, su[)posed to prevail in whole families, in which the disk and not the margins are placentiferous, have lately been assumed by Professor Lindley, Orchidece and Oroban- cliecB being the examples of this structure to which he more particularly refers.
The accurate determination of this question appears to me of great importance to the theoretical botanist, but the sub- ject will be most advantageously discussed after treating of the oricrin and modifications of stis-mata.
An ovarium less manifestly compound is that in which the centre of the cavity is occupied by a placenta entirely unconnected 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 Jon 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 reduced to a single ovulum.
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