Placentation 



121 



In the case of apocarpous pistils, where there are more 

 than one ovule, they are generally arranged along the ventral 

 suture, and the placentation is said to be marginal (^^%. 229 

 and 228, a). In the multilocular syncarpous pistil the ovules 

 are generally arranged in the central axis, where the cells of the 

 ovary meet (fig. 228, d), and the placentation is axile. 



When the ovary is unilocular the ovules are arranged either 

 upon the wall (fig. 228, b), or upon slight projections (fig. 228, 

 c), and the placentation is parietal. 



In some cases of a unilocular ovary, as in the Primrose and 

 Pink, the ovules are attached to the end Of the flower-stalk 

 which grows up into the ovary (fig. 230). In this case, which 



Fig. 230. — Unilocular Fig. 231. — Lateral style Fig. 232. — Basilar 

 ovaryof ^o^^cwa, with of Strawberry. style of Alche- 



free central placenta. milla. 



is known as free central placentation, the walls of the ovary 

 are perfectly free from the ovules, as can be seen by cutting 

 the pistil of a Pink or Primrose, when the walls can be cut 

 away, leaving the column of ovules in the centre. 



The style, when present, forms a conducting tube from the 

 stigma to the ovary. In the Violet and Flowering Rush it 

 consists of a perfectly hollow tube ; more often, although 

 hollow at first, it becomes afterwards filled up by the growth 

 of ' conducting tissue,' so that at the time of fertilisation no 

 channel is evident. As a rule the style grows from the top of 

 the ovary, when it is said to be terminal. If it springs out 

 from the side, as in the Strawberry (fig. 231), it is lateral ; if 

 from the base, as in the Alchemilla (fig. 232), it is basilar 



