THE PISTIL. 



67 



the placentas are then parietal, and the ovary one-celled {Erythr(ea,&g. 387; Poppy, 



fig. 388) ; the septa are complete if their edges meet in the axis of the flower ; a 



prolongation of the receptacle sometimes traverses this axis, 



which then forms a column (columella : Mallow, Tulip, fig. 



389 ; Campanula, fig. 390) ; through this column, whether in 



its origin it be receptacular, or (as is more usual) through 



the placentas, the nourishment of the ovules is conveyed, as well 



as through the carpels. When the septa are complete, there are 



as many cells as carpels, and the compound ovary is two- or 



more celled {ov. duo- pluri-loculare); and the placentas, united in 



pairs (two to each carpel), are central. 



The septa are usually formed from the endocarp of the carpels, with an 

 interposed expansion of the mesocarp. Spurious dissepiments [d. spuria) are vertical 

 or horizontal septa, which are not formed by the union of the inflexed faces of two 

 contiguous carpels; thus, in Astragalus (fig. 391), the solitary carpel is almost two- 

 celled by an intruded vertical plate formed by a fold of the dorsal face ; in Flax 

 (fig. 392), where there are ten septa, five project from the midribs of the carpels 

 towards the axis, which they do not always reach. In Datura (fig. 393), the three 

 carpellary ovary is four-celled from the inflexed contiguous faces of the carpels, after 

 uniting in the axis, being reflexed inwards, and meeting a prolongation from the 

 midrib of the carpel : the placentas are thus borne on a septum composed partly of 



. Campanula. 

 Ovary cut transversely. 



391. Astragalus. 



lEtipe pistil, 



open. 



392. Flax. 



Qvary cut transversely, 



presenting 



five septa and 



five half-septa. 



S93. Datura. 

 Centre of ovary 

 cut transversely. 



394. Datura. 



Top of ovaiy 



cut transvei-sely. 



SOS. WalMower. 



Young ovary (mag.) 



cut transversely. 



the inflexed and then reflexed carpellary faces, and partly of a prolongation from 

 the midrib. In the upper part of the ovary, the accessory septa (formed from the 

 midrib) disappear, and two cells only are seen (fig. 394). In the Wallflower, and 

 allied plants (fig. 395), the two carpels are pressed together; along each of their two 

 edges runs a double seed-bearing fibro-vascular bundle ; these are the four placentas 

 arranged in pairs ; the pistil is two-celled, by a delicate and almost transparent 

 false septum, to which the placentas form a sort of frame. This septum is supposed 

 to be formed by the placentas ; for, when young, it is seen to be composed of four 

 plates, which spring in pairs from each pair of placentas, and advance inwards till 

 they join together ; later, this false septunr appears formed of a single membrane, 

 but it retains in the centre the trace of its double origin, in a vertical median line, 

 along which it is easily divided without tearing. 



In Coronilla and Cassia (fig. 502), the young carpel is one-celled, but at a later 



f2 



