STIC^rA AND PARIETAL PLACKNT.^ IN PLANTS. 557 



manifest in a monstrosity of Tropceolnm wnjiis, \w \\\\vA\ tlie 

 stamina arc converted into pistilhi; l)nt the complete action 

 beiiio^ impeded by the presence of the regnlar trilocular 

 pistillnm, and the two mari^inal cords of each open ovarium 

 remaining distinct, the origin of the ovulum from one only 

 of tliese cords is satisfactorily shown. 



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

 placenta3 ])roject 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 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 

 exceptions, su[)posed to prevail in whole families, in which 

 the disk and not the margins are placentiferous, have lately 

 been assumed by Professor Lindley, Orchidece and Oroban- 

 cliecB 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 oricrin and modifications of stis-mata. 



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 Jon 

 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. 



