CHAP. II. 
OVARY. 
199 
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. There can be no doubt that the 
plan of all carpels is the same ; so that the ovary is the blade 
of a leaf, the style an elongated midrib, and the stigma the 
denuded, secreting, humid 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 at some part of the ventral suture that is formed the 
placenta, which is a copious developement of cellular substance, 
out of which the ovules or young seeds arise. It, the placenta, 
originates in both margins of the carpellary 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 be 
two obvious placentae to each carpel. Now, as the stigma is 
the termination of the dorsal suture, it occupies the same 
position as that suture with regard to the two placentae ; con- 
sequently the normal position of the two placentae of a single 
carpel will, if they are separate, be right and left of the 
stigma. This is a fact important to bear in mind. 
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 
they are completely united into an undivided body, as in 
Pyrus, they are syncarpous. That syncarpous pistils are really 
made up of a number of united carpels is easily shown, as 
o 4 
