STIGMxV AND PARIETAL PLACENTAE IN PLANTS. 557 



manifest in a monstrosity of Tropeeolum majiis, in which the 

 stamina are converted into pistilla; but the complete action 

 being impeded by the presence of the regular trilocular 

 pistillum, and the two marginal cords of each open ovarium 

 remaining distinct, the origin of the ovulum from one only 

 of these cords is satisfactorily shown. 



Au ovarium with two or a greater number of cells, whose 

 placentse project 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 js. to form a parietal placenta, often apparently 

 simple, but in reality double in al.1 cases. This view of the 

 composition of a unilocular ovarium having two or more 

 parietal placentcE is also very generally received. But 

 exceptions, supposed to prevail in whole families, in which 

 the disk and not the margins are placentiferous, have lately 

 been assumed by Professor Lindley, OrcJddece and Oroban- 

 chece 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 origin and modifications of stigmata. 



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 pm 

 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. 



