482 



HUTCHINSON'S POPULAR BOTANY 



FIG. 595. LUPIN 



(Lupinus). 

 The fruit is a legume. 



term is simply a diminutive of the latter a fact which 

 gives the key to a definition. BrieHy, indeed, a silicula 

 is a broad and very short siliqua. The ubiquitous 

 Shepherd's Purse (Capsella bursa-pastoris) offers the 

 readiest example of this form of fruit ; but, for variety's 

 sake, we have chosen for illustration a silicula of the 

 Evergreen Candytuft (Iberis sempervirens, fig. 603). 



It will be noticed that the capsule, follicle, legume, 

 siliqua, and silicula are all forms of dry dehiscent fruits. 

 Fleshy or succulent pericarps 

 have no place in this fivefold 

 group. Nevertheless there are 

 two forms of dehiscent fruits in 

 which the characteristic alluded 

 to is met with namely, the suc- 

 culent capsule and the dehiscent 

 drupe. 



The green prickly husk of 

 the Horse-chestnut (^Esculus kip- 

 pocantanum, fig. 590) is a peri- 

 carp, which, when ripe, splits 

 into valves and sets free the 

 large red-brown seeds the so-called "nuts." It is 

 a succulent capsule. So, too, is the unarmed fruit 

 of the nearly related Sweet Buckeye (Pavia, flavci), 

 whose native habitat is the mountainous districts 

 of Tennessee and North Carolina. 



The Walnut (Juglans regia) is a dehiscent drupe. 

 Its green fleshy covering consists of epicarp and 

 mesocarp. The hard shell enclos- 

 ing the seed is endocarp. The 

 fleshy covering, which is rich in 

 tannin, protects the unripe seed 

 from nut-cracking animals; but 



when the seed is ripe, the envelope splits and curls away, 

 and the so-called "nut" (whose development is really 

 analogous with that of a plum-stone) drops to earth. It 

 is still protected by the thin but stony shell, and even 

 when that is broken there is the bitterness of the skin to 

 give the seed a final chance. 



The curious hooked fruits of the Martynias are sub- 

 drupaceous capsules. Frank Buckland used to say of 

 Martynia proboscidea that its fruits must have been created 

 "for the express purpose of sticking to the tails of the 



FIG. 596. STOCK 



(Matthiola annua). 



A siliqua, and the same dehiscing. 



FIG. 597. LUCERNE 

 { Medicago saliva). 



The fruit is a spiral 

 legume. 



