322 THE FRUIT. 



it undergoes various transformations, analogous to those which take 

 place in other parts of the plant. 



588. Most pulpy fruits are tasteless or slightly bitter during their 

 early growth ; at which period their structure and chemical com- 

 position is similar to that of leaves, consisting of cellular with some 

 woody tissue ; and their action upon the atmosphere is likewise the 

 same (346). In their second stage, they become sour, from the 

 production of acids (353), such as tartaric acid in the grape ; the 

 citric in the lemon, orange, and the cranberry ; the malic in the 

 apple, gooseberry, &c. At this period they exhale very little ox- 

 ygen, or even absorb that substance from the surrounding air. 

 The acid increases until the fruit begins to ripen, when it gradu- 

 ally diminishes, and sugar is formed. In the third stage, or that of 

 ripening, the acids, as well as the fibrous and cellular tissues, grad- 

 ually diminish as the quantity of sugar increases ; the latter be- 

 ing produced partly at the expense of the former, by transforma- 

 tions which are very intelligible to the chemist, and which he can 

 partially imitate. A chemical change, similar to that of ripening, 

 takes place when the green fruits are cooked ; the acid and the 

 mucilaginous or other products, by the aid of heat reacting upon 

 each other, are both converted into sugar. Mingled with the sac- 

 charine matter, a large quantity of vegetable jelly (83) is also 

 produced in most acidulated pulpy fruits, existing in the form of 

 pectine and pectic acid. These arise from the reaction of the 

 vegetable acids during ripening upon the dextrine and other assim- 

 ilated neutral products accumulated in the fruit. 



589. Frequently different parts of the thickness of the pericarp 

 undergo dissimilar changes during fructification and ripening ; the 

 inner portion hardening while the exterior becomes fleshy, or vice 

 versa. When the walls of a pericarp are thus distinguished into 

 two separable portions, the exterior receives the name of EPICARP, 

 or EXOCARP, and the interior that of ENDOCARP. When the exte- 

 rior part is fleshy or pulpy, as in the peach (Fig. 447) and plum, 

 it is termed the SARCOCARP ; and the hard shell or endocarp which 

 contains the seed is called the PUTAMEN. 



590. Often the walls of the pericarp preserve a nearly uniform 

 texture throughout, becoming either entirely membranaceous, as in 

 many capsules or pods ; or fleshy, as in the berry ; or indurated 

 throughout, as in the acorn. 



591. A part, and in membranaceous or other dry fruits the 



