108 



COMPOUND PISTILS. 



[SECTION 10 



Such a pistil is just what would be formed if the simple pistils (two, three, 



or five ill a circle, as the case may be), like those of a Pa;ouy or Stonccrop 



(Fig. 224, 225), pressed together in the centre of the flower, 



■were to cohere by their contiguous ))arts. In such a case 



the placenta} are naturally aaile, or all brought together in 



the axis or centre ; and the ovary has as many Dissepiments, 



or internal Partitions, as there are carpels in its composition. 



For these are the contiguous and coalescent walls or sides of 



the component carpels. When such pistils ripen into pods, 



they often separate along these lines into their elementary 



carpels. 



311. One-celled, with free Central Placenta. The 

 commoner case is that of Purslane (Fig. 272) and of the 

 Pink and Chickweed families (Fig. 381, 332). This is ex- 

 plained by supposing that the partitions (such as those of 

 Fig. 329) have early vanished or have been suppressed. In- 

 deed, traces of them may often be detected in Pinks. On the other liana, 

 it is equally supposable that in the Primula family the free central is de- 

 rived from parietal placentation by the carpels bearing ovules 

 only at base, and forming a consolidated common placenta 

 h\ the axis. Mitella and Dionsea helj) out this conception. 



312. One-celled, with Parietal Placentae. In this not 

 uncommon case it is conceived that the two or three or 

 more carpel-leaves of such a compound pistil coalesce by 

 tiieir adjacent edges, just as sepal-leaves do to form a gamo- 



sepalous calyx, 



tion, Fig. 334. Here each carpel 

 bearing ovules along its margins : 



or petals to form 

 a gamopetalous 

 core 



is si 

 d 



33;^ 



actual cross-sec- 

 is an open leaf, or with some introflexion; 

 and each placenta consists of the con- 



)rolla, and as ^B^^) 



shown in the 1 I 



iagram,Fig. iJ 



53, and in an Wr 



, , 333 



Fig. 3.31, 332. Pistil of a Sandwort, witli vertical ami transverse section of the 

 ovary : free central placenta. 



Fig. 3-33. Plan of a one-celled ovary of three carpel-leaves, with parietal pla- 

 centae, cut across below, where it is complete; the up])er part showing the top of 

 the three leaves it is composed of, approaching, but not united. 



Fig. 334. Cross section of the ovary of Frost- weed (Helianthenium), with three 

 parietal placentae, bearing ovules. 



Fig. 335. Cross section of au ovary of Hypericum graveolens, the three large pla- 

 centa? meeting in the centre, so as to form a three-celled ovary. 336. Same in fruit 

 tlie placentae now separate and rounded 



