ELEMENTS OF STRUCTURAL HOTANY. 'Jl 



ated from each other by a douhh nail, aud that the 

 seeds would be fouud arranged about the centre or axis 

 oUhe pistil; and this is the actual state of thin-sin 

 the Tulip, %vhose pistil is formed by the union of three 

 carpels. When the pistU ripens, the double walls sepa- 

 rating the cells split asunder. To these separating 

 ■walls the name dis.'^t'ijivu-nt or (Xirtitiun is given. 



liO But it often happens that tliough several car- 

 pels unite to form a compound pistil, there is but one 

 cell in the ovarv. This is because the separate carpcl- 

 lary leaves have not been folded before uniting, bu 

 have been joined edge to edge, or 

 rather with their edges slightly 

 turned inwards. In these cases the ^^ 

 seeds cannot, of course, he in the ^.^ ^.^ ^.^ '^^ 

 centre of the ovary, but will be found 



on the ivalls, at the junction ot the carpels 

 (Figs. 150, 151). In some plants the ovary 

 ^ is one-celled, aud the seeds are arranged 

 W round a column which rit^es from the bottom 

 f of the ct'U (Figs. 152, 15^. This case is 



Fi"s 1-,. 153 explained by tbe early obliteration of the 

 partitions, which must at fast have met in the centre of 



the cell. 



Ul In all cases the line or projection to which tl o 

 seeds are attached is called the placenta, and the tenu 

 placentation has reference to the manner m w iich 

 the placentas are arranged. In tlio simple pistil the 

 placentation is n.ar.jh.'f or sutural. In the syncarpous 

 pistil if the dissepiments meet in the centre of the 

 ovary, thus dividing it into s. parate cells, the placenta- 

 tion is central or a.-ile ; if the ovary is one-celled r.na 

 bears the seeds on its walls, the placentation i^varvcto • 



