240 MANUAL OP BOTANY 



disposition of the sutures. When an ovary, on the contrary, is 

 formed of the blades of two or more carpellary leaves, the 

 margins of which are not inflected, or only partially so, and is 

 therefore one-celled, and the placentation parietal or free central, 

 both ventral and dorsal sutures may be observed externally, 

 alternating with each other. The fruit, which is formed in a 

 similar manner, necessarily presents a similar alternation of the 

 sutures on its external surface. 



Dehiscence. — The pericarp at varying periods, but commonly 

 when the fruit is ripe, may open, so as to allow the seed or seeds 

 to escape ; in other cases it remains closed, and the seeds can 

 then only become free by its rupture or decay. In the former 

 case the fruit is said to be dehiscent ; in the latter, indehiscent. 

 Those fruits, such as the Nut, Cherry, Apricot, Plum, and Date, 

 which have very hard or fleshy pericarps, are usually indehis- 

 cent. 



Dehiscent fruits open in various ways : — 1st. By splitting 

 longitudinally, either in the lines of the dorsal sutures, or at the 

 junction of the component carpels only, or at these points 

 as well as at the dorsal sutures. In all the above cases the 

 pieces into which the fruit separates are called valves, and these 

 valves, when the fruit is normal in its structure, are either equal 

 in number to the cells, or component carpels, or they are twice 

 as numerous. In fruits formed of a single carpel, which only 

 open by the ventral or dorsal suture, there will be only one valve 

 {figs. 510 and 511), corresponding to the one carpel ; but if the 

 carpel opens by both sutures {fig. 512), there will be two valves. 

 In fruits composed of several cells the valves will be equal in 

 number to the component carpels, if the dehiscence only takes 

 place by the dorsal suture (_/7'grs.516and517), or in the line of union 

 of the component ovaries {figs. 513and514) ; or they will be double 

 the number, if the dehiscence takes place by both these parts. 

 In polycarpellary one-celled fruits the valves will be equal in 

 number to the component carpels, if the dehiscence occurs only 

 by the ventral {fig. 522) or dorsal sutures {fig. 515) ; or double 

 the number, if by all the sutures. "When there is a distinct axis 

 left after the separation of the valves, this is called the cohimella 

 {fig. 543, a). 2nd. Dehiscence, instead of taking place longi- 

 tudinally, or in a valvular manner, sometimes occurs in a 

 transverse direction, by which the upper part of the fruit sepa- 

 rates from the lower like the lid from a jar or box. 3rd. It may 

 take place in an irregular manner by little pores. We have thus 

 three kinds or classes of dehiscence, which are called respec- 



