104 



HKSCR1PTIVE BOTANY. 



PART I. 



have manifested a decided tendency to develop in 

 the form of leaves, and where the position of the 

 ovules is marked on their edges by small projections 

 (fig. 105.). 



If we suppose five carpels, formed 

 on the same general principle as 

 that of the pea-pod, to be ar- 

 ranged round an axis, and to be en- 

 veloped in a mass of pulpy matter, 

 contained in a swollen calyx (as 

 in the apple blossom), we have such 

 syncarpous fruits as apples, pears, &c. (fig. 106.). 



A multitude of examples might be adduced, where the 

 compound structure of the pericarp is easily referable 

 to an aggregation of several carpels. In such cases, 

 each carpel forms a distinct " cell ;" and the wall of se- 

 paration between two contiguous cells, is termed a " dis- 

 sepiment" {fig. 107.). There are, however, 

 many pericarps, which, in their nascent state, 

 possess this structure, but become further 

 modified as they ripen, by the rupture and 

 subsequent obliteration of the dissepiments; 

 at the same time the placentae coalesce round 

 the axis, so that the ripe fruit consists of a single cell, 

 formed by an outer shell, which is entirely detached 

 from a central placenta bearing the seed (fig. 

 This is the case in the seed-vessels of pinks, 

 primroses, &c. In some cases, the edges 

 of the adhering carpels do not extend so far 

 inwards as to reach the axis, and then the 

 dissepiments are not complete, as in the 

 poppy (fig. lOQ.). In other cases, the edges 

 of the contiguous carpels meet without ex- 

 tending inwards at all, and then the placenta? 

 are said to be " parietal," because they are 

 placed on the inner surface of the shell 

 which forms the one-celled capsule, as in the violet 

 (fig. 110.). The pericarp is essentially composed of 

 three parts, analogous to those in the leaf two skins, and 



