138 STRUCTURAL BOTANY 



is the development of a layer of very thick-walled, 

 elongated cells (sclerencliyma) from the inner paren- 

 chyma, adjoining the epidermis which lines the cavity 

 of the fruit. The parenchyma lying between the 

 sclerenchymatous zone and the outer epidermis contains 

 chlorophyll. The outer epidermis is densely clothed 

 with overlapping hairs of the usual Wallflower type, 

 and has numerous stomata. 



FIG. 50. Tranverse section of half-ripe fruit of Wallflower 

 (seeds omitted), d, d, thin portions of ovary Avail, where 

 dehiscence takes place ; s, s, septum, which is in two 

 parts. The thick masses of tissue at the two ends of 

 the septum belong to the replum. Magnified about 8. 

 (R. S.) Cf. Fig. 49*, and Figs. 9, 10, 11, pp. 19-21.) 



As the fruit matures, its tissues give up their water 

 and become dry and rigid. When quite mature, it 

 splits open, or dehisces, owing to the unequal contrac- 

 tion of the harder and softer layers of the carpellary 

 walls. The sides of the fruit split away from the 

 replum or persistent placenta, the severance beginning 

 below and extending upwards. The valves thus 

 formed remain for a time attached at the top (Fig. 

 49*, 2). When they fall the replum is left intact, 



