STRUCTURE.] MOKPHOLOGY OF THE CARPEL. 371 



pistil loses its normal carpellary character, and reverts to the 

 structure of the leaf. In this plant the pistil is a little con- 

 tracted leaf, the sides of which are pressed face to face, the 

 midrib elongated, and its apex discoloured, or a little dis- 

 tended. If we compare this with the pistil of a single cherry, 

 the margins of the leaf with the ventral suture, the elongated 

 midrib with the style, the discoloured distended apex with the 

 stigma, they will be found to correspond exactly. 



In this case there is an indisputable identity of origin and 

 nature between the ovary and the blade of a leaf; between 

 the little suture that occupies one angle of the carpel of a 

 cherry, and the line of union of the two edges of the leaf; 

 and between the elongated midrib, with its distended apex, 

 and the style and stigma at least in part. There can be no 

 doubt that the plan of many carpels is the same ; so that the 

 ovary is in such cases the blade of a leaf, the style an elongated 

 midrib, and the apparent stigma the apex of the latter. 



Such being the origin of the carpel, its two edges will cor- 

 respond, one to the midrib, the other to the united margins 

 of the leaf. These edges often appear in the carpel like two 

 sutures, of which that which corresponds to the midrib is called 

 the dorsal, that which corresponds to the united margins is 

 named the ventral, suture. 



It is often at some part of the ventral suture that is formed 

 the placenta, which is a copious development of cellular sub- 

 stance, out of which the ovules or young seeds arise. It, the 

 placenta, is usually connected with both margins of the car- 

 pellary leaf : but, as they are generally in a state of cohesion, 

 there appears to be but one placenta; nevertheless, if, as 

 sometimes happens, the margins of the carpellary leaf do not 

 unite there will in such cases be two obvious placentae to each 

 carpel. Now, if the stigma is the termination of the dorsal 

 suture, it will occupy the same position as that suture with 

 regard to the two placentae ; consequently the normal posi- 

 tion of the two sutural placenta of a single carpel will, if 

 they are separate, be right and left of the stigma. 



Pistils consisting of but one carpel are simple ; of several, 

 are compound. If the carpels of a compound pistil are dis- 

 tinct entirely or in part, they are apocarpous, as in Caltha ; if 



B B 2 



