THE ANGIOSPERMAE 1535 



In septate fruits there are three patterns of longitudinal dehiscence. Locu- 

 Ucidal: The carpels may split down their dorsal sutures, thus opening directly 

 into each loculus. Septicidal: the splits separate the carpels entirely from 

 each other, thus dividing each septum into two. Septifragal: the carpels 

 split opposite the outer end of each septum, the outer walls being detached 

 and the septa remaining attached to the central axis. 



All but a minority of capsules dehisce by one or other of these methods. 

 The exceptional cases may be mostly classified under the three following 

 types. Porose: the carpel walls open by means of small localized openings, 

 where the tissues split apart. A common example of this is the capsule of 

 the Poppv, whose outer wall shrinks in drying and separates from the 

 stigma-bearing cap of the fruit, leaving a gap all round under the edge ot the 

 cap. The gap is divided into pores by the outer edges of the false septa, 

 which are exposed by the opening. The seeds are scattered by the shaking 

 of the capsule on its long stalk in the wind. Circumscissile : the line of dehis- 

 cence girdles the capsule transversely, detaching a lid. This is not common 

 but is seen in Plantago, Anagallis and Hyoscyamiis, all well-known plants. 

 Valvate: the capsule opens at the top by the separation of the tips of the 

 carpels, which bend outwards, exposing the interior. The fruits of the 

 Caryophyllaceae are valvate in many genera. 



When a capsule is unilocular the mode of dehiscence is naturally some- 

 what modified, as there are no septa. In such types the carpels usually 

 separate at their edges, which is most nearly analogous to septifragal 

 dehiscence. The circumscissile capsule of Atiagallis (see above) is an 

 exception. 



Capsules which dehisce longitudinally mostly separate into as many 

 segments as there are carpels, but occasionally there are supernumerary 

 splits. For instance, the capsule of Datura consists of two carpels but the 

 capsule wall splits into four valves. The dehiscence is truly septifragal but 

 each carpel splits secondarily along its midrib, opposite the false septum 

 formed by the placentae (Fig. 1397). 



Dehiscence of fruits is generally brought about by the shrinkage of 

 the pericarp in drying but in the fruits with stony endocarps to be des- 

 cribed later, it is the swelling of the contained seeds as they take up water 

 which forces open the hard shell around them. 



If some akenes can be regarded as reduced follicles, others may 

 equally be looked upon as reduced capsules. This is the case with the Nut 

 where reduction has, by definition, occurred. The inferior nut or glans 

 of Corylus arises from a bicarpellary ovary of which one only is fertile. The 

 septum adheres to the inside of the pericarp, except for its central strand, 

 which remains, attached to the ripe seed, as a woody cord at the top of 

 which is attached the shrivelled ovule of the infertile carpel (Fig. 1398). 

 The samara of Fraxinus has the same structure except for the wing, the 

 plane of which is perpendicular to the septum. The samara of I'hmis is a 

 parallel case, though one carpel is sterile from the beginning. The cremo- 

 carps also may be classed as reduced bicarpellary capsules, in their case 



