ESSENTIAL FLORAL LEAVES. 105 



spond to the united edges, for at each of them is a ridge-like pla- 

 centa bearing ovules. This kind of placentation is parietal (fig. 

 48, E). The same term is applied where the united carpels are 

 partly folded, so that the single loculus is divided into chambers 

 at its margin. Thus in poppy there are a great many chambers, 

 and the parietal placentas, which bear an immense number of 

 minute ovules, project into the ovary. This can easily be verified 

 in the dried poppy-heads sold by druggists (cf. fig. 48, F). 



Some ovaries are divided up by false or spurious dissepiments, 

 so called because they are not partitions formed by union of 

 adjacent carpels, but outgrowths from the wall of the ovary. In 

 yellow corydal and Dielytra, both common garden plants, the 

 syncarpous pistil is formed by the union of two lateral carpels. 

 The ovary is unilocular, and the ovules are borne on two parietal 

 placentas, one anterior, the other posterior. Wallflower, stock, 

 and shepherd's purse, which are not very distantly related, pre- 

 sent precisely the same arrangement, with this exception — the 

 ovary is divided by a partition into right and left halves. This 

 evidently does not correspond to the infolded edges of carpels, or 

 the placentation would be axile. It is, however, parietal, and 

 this fact, supported by comparison with the allied dielytra, &c, 

 prove the partition to be an ingrowth. A study of the develop- 

 ment confirms this view. Again, in dead nettle and sage the 

 end of the style forks into anterior and posterior branches, which 

 leads one to suspect the existence of two carpels, one anterior, 

 the other posterior. The ovary, however, is /bw?--lobed, and con- 

 tains four loculi. This points to four carpels. The evidence 

 given by the style is here really correct. Development shows 

 that two is the actual number, but an ingrowth occurs from the 

 dorsal margin of each carpel, dividing its cavity into two. Borage, 

 forget-me-not, and their allies present the same feature, but are 

 even more misleading, since in them the style is undivided, or at 

 most slightly notched. 



The inferior syncarpous ovary (fig. 48, C), though its outer wall 

 is partly formed by the cup-like receptacle, corresponds very 

 closely in form and placentation with the superior syncarpous 

 one. Snowdrop and orchis will here serve, respectively, as 

 examples of axile and parietal placentation. 



There are still other ways in which ovules may be arranged. 

 Each one of the ten carpels of the flowering rush contains a large 

 number of ovules which are scattered over the walls of the loculus, 

 and not limited to the united margins. This is superficial pla- 

 centation. It is a rare form, but also occurs in the syncarpous 

 pistils of white and yellow waterlilies. 



Transverse and longitudinal sections of the ovary of a pink or 



