140 HLKMENTS OP STRUCTURAL BOTANY. 



are united below but separate above. Sometimes, also, 

 false partitions are formed across the loculi in the cours* 

 of growth. In tlie Mints, for instance, there are at 

 first but two loculi ; eventually, however, there are four, 

 which completely separate at the time of ripening. 



220. But it often happens that though several carpels 

 unite to form a compound pistil, there is but one cell 'in, 



the ovary. This is because the separ- 

 ate carpellary leaves have not been 

 folded before uniting, but have been 

 joined edge to edge, or rather with 

 Pig. 193. Fig. 192. their edges slightly turned inwards. 

 In these cases the seeds cannot, of course, be in the 

 centre of the ovary, but will be found on the walls, at 

 the junction of the carpels (Figs. 192 and 193). In 

 some plants the ovary is one-celled, and the seeds are 

 arranged round a column which rises from the bottom of ' 

 the cell (Figs. 194 and 195). This case is 

 explained by the early obliteration of the 

 partitions, which must at iirst have met in 

 the centre of the cell. Special cases, how- 

 ever, are found in which no trace of parti- 

 tions has been observed, and these must 

 consequently be explained by the actual '®' ' , '^' 

 Upward growth of the axis into the centre of the ovary. 



221. In all cases the line or projection to which the 

 seeds are attached is called the placenta, and the term 

 placentation has reference to the manner in which 

 the placentas are arranged. In the simple pistil the 

 placentation is marginal or sutural. In the syncarpous 



Figs. 192, 193. — Compound one-celled ovary of Mignonette. 

 Figs. 194, 195,— Sections of ovary of a Pink, showing free central pla- 

 centation. 



