DEHISCENT FRUITS. 



257 



by giving way only on the margins within the sutures, where the 

 placentas are united ; and when the valves fall off, the placentas are 

 left in the form of three arched repla or frames, to which the seeds 

 are attached. In the case of a free central placenta, when the valves 



separate, it is sometimes difficult to tell whether the dehiscence is 

 septicidal or loculicidal, inasmuch as there are no dissepiments, and 

 the placentas and seeds form a column in the axis. Their number, 

 as well as their alternation or opposition, as compared with the sepals, 

 will aid in determining whether the valves are the entire carpeUary 

 leaves, as in septicidal dehiscence, or only halves united, as in loculi- 

 cidal. In some instances, as in Linum catharticum, the fruit opens 

 first by loculicidal dehiscence, and afterwards the carpels separate in 

 a septicidal manner. 



535. Another mode in which fruits open is transversely, the dehis- 

 cence in this case being called circumscissile (circum, around, and 

 stindo, I cut). In such cases, the fruit or seed-vessel may be supposed 

 to be formed by a number of articulated leaves like those of the 

 Orange, the division taking place where the laminae join the petioles. 

 In this dehiscence, the upper part of the united valves falls off in the 

 form of a lid or operculum, as in Anagallis (fig. 458), and in Hyos- 

 cyamus (fig. 459), and hence the fruit is often denominated operculate 

 (operculum, a lid). In some instances the axis seems to be prolonged 



Fig. 455. Fruit or mature carpel of Geranium sanguineum. c, Persistent calyx, o, Axis 

 prolonged as a beak. 1 1, The styles, at first united to the beak, and afterwards separating from 

 below upwards, along with the carpels, o o, which dehisce by their dorsal suture, s. Stigmas. 

 The fruit is sometimes called gynobasic. 



Fig. 456. Siliqua of Cheiranthus Cheiri, Wallflower, dehiscing by two valves, v v, which 

 separate from a frame or replum, r. gr, Seeds arranged on either margin, s, Two-lobed stigma. 



Fig. 457. Capsule of Orchis maculata at the period of dehiscence. c, Remains of the limb of 

 the calyx crowning the fruit v v, Segments of the pericarp which are detached in the form ot 

 valves, p p, Arched repla or placentas which remain persistent, and bear the seeds. 



S 



