OP THE FRUIT. 765 



when first formed, it'produdes similar changes to the leaves ; but 

 when of other colours than green, and more especially when 

 succulent, it evolves carbonic acid gas at all times, instead of 

 oxygen gas, as in the former cases, under the influence of solar 

 light. 



The chemical constitution of fruits varies according to their 

 nature and age. When the pericarp is of a dry nature, it com- 

 monly assumes a whitish or brownish colour, and its cells become 

 incrusted with hardened matters Qignine). Under such circum- 

 stances, no further changes take place in its chemical con- 

 stitution, and its vital activity ceases. When the pericarp, 

 however, becomes of a succulent nature whilst ripening, it 

 assumes various tints ; transpiration goes on from its outer 

 cells, the contents of which thus becoming of a denser nature, 

 absorb the watery matters from those within them, and these 

 in like manner react upon the contents of those within them, 

 so that there is a constant passage of fluid matters from the 

 surrounding parts by endosmotic action into the pericarp 5 in 

 this way, therefore, it continues to enlarge, until it has arrived 

 at maturity, when transpiration nearly ceases from the deposi- 

 tion of waxy matter in or upon the epidermal cells, and the 

 stalk by Avhich it is supported to the plant becomes dried up. 



Tiie chemical constitution of succulent pericarps varies ac- 

 cording to their age. When first formed they have a like com- 

 position with leaves, and have but little or no taste. After a 

 time they acquire an acid flavour from the formation of vegetable 

 acids, and salts with an acidreaction. The nature of these acids 

 and salts varies in different fruits ; thus the Grape contains 

 tartaric acid chiefly and bitartrate of potash, the Apple, mahc 

 acid, and the Lemon, citric acid. As the pericarp ripens, sac- 

 charine matter is formed, and the quantity of free acids dimi- 

 nishes, partly from their conversion into other matters, and 

 partly from their combination with alkalies. In order that these 

 changes may be properly eff'ected, it is necessary that the fruit 

 be exposed to the sun and air, for if grown in the dark, it will 

 continue acid; and will be moreover, much less sweet when de- 

 veloped in diifused daylight, than when freely exposed to the 

 sun. As fruits ripen they evolve carbonic acid gas, as already 

 noticed, give ofi" watery fluids, and a sensible elevation of 

 temperature may be noted. 



The origin of the sugar of fruits, and even its nature, is not 

 satisfactorily detei'mined. • According to most observers, ripe 

 fruits contain grape sugar, but M. Buignet has lately stated, that 

 the sugar which is primarily formed in acid fruits is cane sugar 

 (C,2 H,, 0,,), and that during the process of ripening, this 

 sugar is gradually changed into interverted sugar (C,2 H12 O12), 

 but very often there remains in the ripe fruit a mixture of these 

 two sugars. The origin of the sugar is variously attributed 



