THE ESSENTIAL OEGANS THE PISTIL. 129 



Placenta, Sutures. The region of the carpel whence the ovules 

 arise is called the placenta ; and when in Angiospermous flowers 

 the placentas are clearly and distinctly marginal, they must of 

 course be double, from the meeting of the two edges ; the same is 

 true of the stigmatic surfaces. The line of union of the margins 

 of carpels constitutes the ventral suture : the line corresponding to 

 the midrib of the carpellary leaf is the dorsal suture. 



An excellent example of a simple typical pistil formed of a single carpel 

 is afforded by the legume of the LeguminosEe ; as, for instance, in the 

 Sweet-pea, where we find the ovary, with a ventral and dorsal suture, 

 narrowed above into a short slender style, terminating in a slightly 

 enlarged stigma. When we open the ovary, in the way it is broken in 

 shelling peas for the table, we find the plaeentary margins separated at the 

 ventral suture, each carrying away half the ovules, demonstrating clearly 

 the double character of the placenta. 



Modifications. Pistils differ extremely in different plants, from 

 dissimilarity in the number, degree, and mode of union of the car- 

 pels, as well as in the relative degree of development of the different 

 regions of the carpels, and with these may be associated the pecu- 

 liarities arising from adhesion of the outer circles. 



Numerical relation. The number of carpels is most frequently 

 less than that of the organs in the outer whorls, being very fre- 

 quently reduced to two, and often to one. On the other hand, 

 multiplication of the number is met with in certain Orders, where 

 the receptacle is generally more or less enlarged to make room for 

 them. 



A large portion of the Gamopetalous Dicotyledons, with a quinary ar- 

 rangement of the calyx and corolla, and often of the stamens, have dicarpel- 

 lary pistils, as Gentianacese, Apocynaceee, Solanacege, &c. Leguminosse 

 with quinary flowers have a solitary carpel. The agreement of the number 

 of carpels with the other organs is almost universal in the ternary flowers 

 of Monocotyledons, as in Liliaceae, Iridacese, Orchidacese, &c. Multiplica- 

 tion of carpels is especially frequent in the Ranunculaceae, Magnoliaceae, 

 and some other Orders. 



Apocarpous Pistil. In the typical pistil above described, and 

 which really exists in Leguminosae (for instance), the organ, being 

 composed of one carpel only, is simple. A carpel may be solitary 

 in a flower, from suppression of the remainder of the circle ; or 

 there may be in the same flower several distinct, i. e. uncombined, 

 carpels, as in Larkspur, Aconite, Magnolia, Ranunculus, Fragaria, 

 &c. : in these cases the terms multiple pistils is occasionally used, 

 or we may say carpels distinct, three, five, or numerous, as the 

 case may be. The term apocarpous pistil includes both the solitary 

 carpel and the multiple pistils. In the case of multiple pistils, 



