THE ANGIOSPERMAE 1531 



3. Dehiscent Dry Fruits. The ripe fruit dehisces to release the seeds, 

 usually several, often many in each carpel. 



(«) Fruits formed of a single free carpel. 



(i) Follicle. A pod-like fruit which splits down one side, 

 generally the ventral side, and occasionally down part 

 of the other side. Examples: Aconitum, Delphinium. 



Among the follicles should be mentioned the remarkable woody fruits 

 of some Proteaceae, in which the fruit wall becomes extremely thick and 

 hard. Only one fruit is formed by each flower, which splits open to release 

 two flattened and delicately winged seeds. Examples: Banksia, Xylomelum, 

 the Woody Pear of Australia, Hakea and Grevillea. In some genera of the 

 family the fruit is indehiscent and one-seeded. The single follicles in this 

 family are unusual. Follicles are generally formed in groups from the 

 clustered carpels in apocarpic flowers. 



(ii) Legume. Like the follicle, this is the product of a single 

 free carpel. It is also many-seeded, but it difi^ers in 

 opening down the full length of both the ventral and 

 dorsal sutures, so that the fruit separates into two halves 

 or valves, with seeds attached alternately to the margin 

 in each half. When separating the valves usually twist 

 rapidly, causing the detachment of the seeds. The 

 tension which results in the sudden dehiscence and 

 tv/isting is due to the diflFerential shrinkage of the soft 

 outer tissues and an inner sclerotic layer of the carpel 

 wall, as the fruit dries in ripening. 



This is the simple legume as it is found in the majority of the Papilion- 

 aceae (Fig. 1394), but there are several variants. In the big genera Astragalus 

 and Oxytropis the united ventral margins grow inwards and form a longi- 

 tudinal septum dividing the seeds into two ranks. The valves in the fruit of 

 Carmichaelia have thickened margins, from which they are detached and 

 fall, the margin remaining like a frame with the seeds attached. 



A frequent form of legume is that called a lomentum in which the valves 

 are constricted between the seeds and break across transversely when 

 ripe, each one-seeded portion falling off as an indehiscent, or sometimes 

 dehiscent (Entada), unit. Example: Onobrychis. Lomentaceous fruits 

 are very common in the Mimosaceae and in many species the thickened 

 margin of the flattened legumes forms a frame, as above, from which 

 the lateral walls drop away separately. The legumes of some of the species 

 of the tropical genus Cassia, e.g., C. fistula, are of astonishing length, 

 up to three feet in some cases. They are blackish, hard, and cylindrical 

 and are provided internally with numerous cross-septa, dividing the fruit 

 into one-seeded portions, which however do not separate like lomenta. 

 These cylindrical fruits are indehiscent and only break up by decay or 

 damage. Other species of Cassia have long, flat pods which dehisce longi- 

 tudinally. 



