188 



GROWTH AND WORK OF PLANTS 



calyx, receptacle, etc., combined with it. The fruit may be 

 formed of a single simple pistil or it may be formed of several 

 simple pistils crowded together (aggregate, or collective fruits), or 

 there may be accessory parts of the flower which reinforce the 

 fruit (accessory or reinforced fruits). 



309. The pericarp. The wall of the ripened ovary is called 

 the pericarp. It is the part of the fruit which envelops the seed, 



and may consist of the car- 

 pels alone, or of the carpels 

 and the adherent part of 

 the receptacle, or calyx. In 

 many fruits the pericarp 

 shows a differentiation into 

 layers, or zones of tissue, 

 as in the cherry, peach, plum, 

 etc. The outer, which is here 

 soft and fleshy, is exocarp, 

 while the inner, which is 

 hard, is the endocarp. An 

 intermediate layer is some- 

 times recognized and is 

 called mesocarp. In such 

 cases the skin of the fruit 

 is recognized as the epicarp. 



Epicarp and mesocarp are more often taken together as 



exocarp. 



310. In general, fruits are dry or fleshy. Dry fruits may 

 be grouped under two heads. Those which open at maturity 

 and scatter the seed are dehiscent. Those which do not open 

 are indehiscent. 



II. INDEHISCENT FRUITS. 



311. The akene. The thin, dry wall of the ovary encloses the 

 single seed. It usually does not open and free the seed within. 

 Such a fruit is an akene. An akene is a small, dry, one-seeded, 

 indehiscent fruit. All of the crowded but separate pistils in. the 



Fig. 148. 



Section of drupe, or stone fruit of peach, 

 showing the fleshy exocarp, stony endocarp, and 

 the "meat" or embryo within. 



