STRUCTURE.] SPURIOUS DISSEPIMENTS. 381 



divides the ovary of Astragalus into two equal portions, are 

 dissepiments : both must be expansions of some other part. 



All partitions whose position is at variance with the fore- 

 going laws are spurious. Such spurious dissepiments are 

 caused by many circumstances, the chief of which are the 

 following : they are caused by expansions of the placenta, 

 as in Crucifers, when they form a partition stretching from 

 one side to the other of the fruit ; or they are mere dilatations 

 of the lining of the pericarp, as in Cathartocarpus Fistula, in 

 which they are horizontal ; or they are internal expansions of 

 the dorsal or ventral suture, as in Amelanchier, Astragalus, 

 and Thespesia, in which they are distinguishable from the 

 dissepiments by not bearing the placentae, and by being 

 opposite the stigma, or by projecting beyond the placentae ; 

 or, finally, they are caused by the sides of the ovary projecting 

 into the cavity, uniting and forming many supernumerary 

 cells, as in Diplophractum. 



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 

 whose ovary 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 ; and then the result 

 is an ovary, which, although composed of many carpels, is 

 nevertheless one-celled (fig. 132.). In such case the disse- 



. 132. 



piments project a short distance only beyond the inner lining, 

 QIC paries, of the ovary, and bearing on their edges the pla- 

 centae, the latter are said to be parietal. In other plants, 



