vii.] THE PISTIL. Si 



21. From the circumstance that the ovules usually 

 develop upon the margins of carpels, it must follow th?,t 

 when two or more carpels cohere, and their margins are 

 infolded so as to meet in the centre of the pistil, the 

 ovules must also be attached in the centre or axis. Their 

 attachment, or placcntation, as it is termed, is axile. You 

 find this well shown in Tulip, where there are three 

 carpels ; Foxglove, where there are two ; and Orange, 

 where there are many cohering. 



But in many syncarpous pistils, although the carpels 

 cohere, their margins are not infolded to such a degree as 

 to reach the centre and become united there into an 

 ovule-bearing axis. When such is the case, the placenta- 

 tion is described as parietal. We find all grades of de- 

 velopment of these dissepiments, from the Violet and 

 Pansy, with parietal placentation (the carpels not being 

 infolded at all, and the ovules arranged in lines upon the 

 inside of the one-celled ovary), to the Tulip, in which the 

 carpels cohere to the centre, and the placentation is con- 

 sequently axile. The pistil of Poppy is intermediate ; the 

 margins of the numerous united carpels which compose 

 it projecting into the cavity of the ovary without quite 



Fie. 55. Transverse section of the FIG. 56. Transverse section < f. 



i-celled ovary of Pansy, showing i -celled ovary of" Garden Pink, 



parietal placentatk n. showing free central placenta- 



ticn. 



reaching to the centre. The placentation of this plant is 

 exceptional, the ovules being spread over the sides of the 

 partial dissepiments, instead of being confined to their 

 inner edges. 



In Pinks and Stitchworts the placentation is axile, but 

 the dissepiments are lost before the ovary is fully grown, 

 so that the ovules are collected in a head in the centre of 

 a i-celled ovary. Such placentation is termed free-central. 

 The same kind of placentation is found in Primrose and 

 O.B. G 



