FEMALE ORGANS. 51 



415. This law will explain the structure of some anomalous 

 pistils, in which the carpels are united into a confused mass ; 

 Ex. the Pomegranate 271 . 



416. As the carpels are modified leaves, they necessarily 

 obey the laws of arrangement of leaves, and are therefore de- 

 veloped round a common axis. 



417. And as they are leaves folded inwards, their margins 

 are necessarily turned towards the axis. A placenta, there- 

 fore, formed by the union of those margins, will be invariably 

 next the axis. 



418. So that if a whorl of several carpels with a marginal 

 placentation unite and constitute a pistil, the placentae of that 

 pistil will be all in the axis. 



419. The normal position of the carpels is alternate with 

 the innermost row of stamens, to which they are also equal 

 in number ; but this symmetry of arrangement is constantly 

 destroyed by the abortion or non-developement of part of the 

 carpels. 



420. The carpels often occupy several whorls, in which case 

 they are usually distinct from each other ; Ex. Eanunculus, 

 Fragaria, Rubus 272 . 



421. Sometimes, notwithstanding their occupying more 

 than one whorl, they all unite in a single pistil ; Ex. Nico- 

 tiana multivalvis, Monstrous Citrons. In these cases the pla- 

 centse of the innermost whorl of carpels occupy the axis, 

 while those of the exterior carpels are united with the backs 

 of the inner ones, as must necessarily happen in consequence 

 of the invariable direction of the placentae towards the axis. 



422. When the carpels are arranged round a convex re- 

 ceptacle (389), the exterior ones will be lowest ; Ex. Ru- 

 bus 272 . 



423. But if they occupy the surface of a tube, or are placed 

 upon a concave receptacle, the exterior ones will be upper- 

 most ; Ex. Rosa 177 . 



424. Whenever two carpels are developed, they are in- 

 variably opposite each other, and never side by side. This 

 happens in consequence of the law of alternate opposition of 

 leaves (191). 



425. When carpels unite, those parts of their sides which 

 are contiguous gTow together, and form partitions between the 

 cavities of the carpels. E 2 



