174 
ORGANOGRAPHY. 
BOOK I. 
sepiment d will be opposite the placentae I, formed by the 
cohesion of the contiguous margins of the carpels A and B. 
5. A single carpel can have no dissepiment whatever, 
6. The dissepiment will always alternate with the stigma ; — 
for the stigma is the extremity of the midrib of the carpellary 
leaf, or of the dorsal suture of the carpel ; and the sides of 
either of these (which form dissepiments) will be right and 
left of the stigma, or in the same position with regard to the 
latter organ as the sides of the lamina of a leaf to its apex. 
Let the triangle, a, Z>, c, represent a 
transverse section of a three- celled®^ 
ovary, of which t?, f are the dissepi- 
ments. The stigmas would occupy a 
position equal to that of the spaces 
5, 5, 5, and would consequently be al- 
ternate with c?, e, fi the dissepiments : 
they could not possibly be placed 
opposite c?, J\ upon any principle of 
structure with which we are acquainted. ® 
This law proves, that neither the membrane which separates 
the two cells of a Cruciferous siliqua, nor the vertical plate 
that divides the ovary of Astragalus into two equal portions, 
are dissepiments ; both are expansions of the placenta, or of 
some other part, in different degrees. 
Such is the structure of an ovary in its most common state ; 
certain deviations from it remain to be explained. We have 
seen that when carpels become syncarpous, they form a pistil, 
the ovary of which has as many cells and dissepiments as there 
are carpels employed in its construction. But sometimes the 
united sides of the carpels do not project so far into the cavity 
of the ovary as to meet in the axis, as in the Poppy ; and then 
the result is an ovary, which, although composed of many car- 
pels, is nevertheless one-celled (j^^.134.). In such case the 
dissepiments project a short distance only beyond the inner 
lining, or paries^ of the ovary, and, bearing on their edges the 
placentae, the latter are said to be parietal. In other plants, 
such as Corydalis, Viola, and Orchis, the carpels are not 
folded together at all, but are spread open and united by their 
