Stigma and Parietal Placenta in Plants. 37 



stinct, the origin of the ovulum from one only of these cords 

 is satisfactorily shown. 



An ovai'ium with two or a greater number of cells, whose 

 placentae 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 to- 

 gether so as to form a parietal placenta, often apparently 

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

 composition of a unilocular ovarium having two or more 

 parietal placentae is also very generally received. But ex- 

 ceptions, supposed to prevail in whole families, in which the 

 disc and not the margins are placentiferous, have lately been 

 assumed by Professor Lindley, Orchidea and Orobanchece 

 being the examples of this structure to which he more par- 

 ticularly refers. 



The accurate determination of this question appears to me 

 of great importance to the theoretical botanist, but the subject 

 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 uncon- 

 nected 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 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 re- 

 duced to a single ovulum. 



These are the principal modifications of the compound ova- 

 rium when forming a simple series ; but it is necessary to ob- 

 serve that both surfaces of the inflected and included portions 

 of the carpels are not unfrequently equally productive of 

 ovula, a structure which is manifest in many Cyriandracece, 

 especially Cyrtandra., although in several other genera of the 

 same family the production is confined to the inner or upper 

 surface of the mai'gin. In other cases the polyspermous ovu- 

 liferous portion or placenta is connected with the inner angle 

 of the cell by a single point only, which may proceed either 

 from the apex or base of the cavity. This modification of 



