44 ELEMENTARY BOTANY. 



ing, which renders the stigma sessile. According as the pistil 

 (or " carpel," as it is sometimes called) is formed 

 igma ^^ ^ single carpellary leaf or of several leaves, it is 

 -Style simple or compound. In a simple pistil, formed 

 bj-- a single leaf folded edge to edge, the seeds are 

 a „ borne on the part of the inner wall which corre- 



.Ovule sponds to the line of union of the edges. This 

 seed-bearing line or part is called the placenta. 

 If two placentas are present, they must have re- 

 sulted from the union of two leaves, edge to edge ; 

 if three placentas, from the union of three leaves, etc. There- 

 fore the presence of two or more placentas is proof of a com- 

 pound pistil. The number of styles often corresponds to the 

 number of leaves entering into the formation of the carpel. 



15. Compound pistils may have a single seed-cavity, or locu- 

 lus, or they may have many cavities (loculi). When the car- 

 pellary leaves have united with each other, edge to edge 

 (Fig. 66) there will be but one cavity. The placentas, or 

 seed-bearing lines, will be situated on the ovary wall, as in 

 the simple pistil ; that is, they will be parietal. If each sepa- 



FiG. 66. Fig. 67. Fig. 68. 



rate carpellary leaf unites edge to edge, and then all the carpels 

 join (Fig. 67) the ovary will have as many cavities as there 

 were carpellary leaves ; the seed-bearing lines will be crowded 

 to the centre and form central placentas. The walls which 

 separate the cavities from one another in case of a multi- 

 locular ovary may become obliterated, leaving the seed-bear- 

 ing column in the centre of a continuous or monolocular 

 cavity, and thus a free central placenta is formed (Fig. 

 68). Examples of this are found in the Purslane, Chick- 

 weeds, Pinks, etc. 



