174 



ORGANOGRAPHY. 



BOOK I. 



(D 



sepiment d will be opposite the placentae wz, I, formed by the 

 cohesion of the contiguous margins of the carpels A and B. 



5. A single carpel can have no dissepiment lohatever. 



6. The dissepiment loill ahvays cdternate 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, b, c, represent a ^31 

 transverse section of a three-celled^ ^ 

 ovary, of which d, e., fstxe the dissepi- 

 ments. The stigmas would occupy a 

 position equal to that of the spaces 

 s, s, s, and would consequently be al- 

 ternate with d, e, f, the dissepiments : 

 they could not possibly be placed 

 opposite d, e, f, 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 (_/?^.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 

 placenta?, 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 



