CHAP. II. 
OVARY. 
203 
principle. In order to make these considerations more clear, 
let Jigs, 125, 126, and 127. represent — Jig, 125. a convex 
receptacle, with distinct carpels ; Jig. 1 26. a concave one, with 
the same; and Jig. 127. a concave one, with the carpels con- 
solidated. In these, a a are the outer row of carpels, h h the 
next, and d d the central row. The relative position of 
these, as the receptacle is convex or concave, will now be 
apparent. 
I have stated that the placenta, however simple it may ap- 
pear to be, is usually produced by the union of two united 
margins of a carpellary leaf: it is, therefore, essentially 
double ; and, accordingly, we find that in polyspermous 
ovaries the ovules are almost always arranged in two rows, 
as in the Pea and Bean, the Quince, the Paeony, &c. 
But there are exceptions to this rule. In Taylor* s Maga- 
zine for Nov. 1837, I have shown that in Orobanchaceae the 
placentae undoubtedly arise from the face of the carpel. That 
their capsule consists of two carpels standing right and left of 
the axis of inflorescence, and with the margins not inflected in 
the form of dissepiments, is incontestable. Yet in Orobanche 
and Phelypaea the capsule has the placentae placed equi- 
distant in pairs upon the face of each valve or carpel, and 
considerably within the margin. In Epiphegus each carpel 
has two intramarginal placentae, which diverge from the 
base upwards, and terminate before reaching the apex. In 
Lathraea there is to each valve but one placenta, which may 
be regarded as two confluent ones occupying the very face of 
the dorsal suture of the carpel. And finally in ^ginetia in- 
dica, and I believe in jT^ginetia abbreviata also, the placenta 
is in like manner confined to the axis of the valve, occupying 
the same position upon the carpels as in Lathraea, but broken 
up into a number of parallel plates of unequal depth, over the 
whole surface of which multitudes of minute seeds are distri- 
buted. If we connect these facts, about which there can be 
no sort of question, with the well known placentation of Fla- 
courtiaceae, Nymphaeaceae, and Butomaceae, we shall find that 
they invalidate the general carpological rule, that the placentae 
belong to the ventral suture of a carpel, and consequently 
alternate with the dorsal; and we shall have to admit that the 
