MATUEATIOK OP THE FEUIT. 76 



changes that occur in the secretions of fruits,, are heat 

 and light ; without which the peculiar qualities of 

 fruits are imperfectly formed, especially in species 

 that are natives of countries enjoying a high summer 

 temperature. It is found that among the effects of a 

 high temperature and an exposure to bright light, is 

 the production of sugar and of certain flavours ; and 

 that under opposite circumstances, acidity prevails.* 

 As sugar is more rich in carbon than vegetable acids, 

 and has no free oxygen as they have, the sweetness 

 of pulpy fruits ripened under bright sunshine may 

 be understood to arise from the decomposition of 

 carbonic gas, and the expulsion of oxygen, being 

 greater under sunshine than in the shade. Another 

 cause may be, the greater facility with which vegeta- 

 ble acids enter into combination with gum and starch, 

 and so form sugar, at a high than at a low tempera- 

 ture.f 



100. One of the most essential of the alterations 



* [Fruits remain acid in cold summers: on the other hand, nearly 

 all the trees of tropical climates produce oils, caoutchouc, and other 

 substances -which contain little or no oxygen. G.] 



f For Table of the Proportions of Carbon and Water in a few of 

 the commonest Vegetable Secretions, vide next page. 



The gummy, mucilaginous, and gelatinous parts appear very sus- 

 ceptible of changing into sugar ; thus M. Couverehel found that, if 

 Apple jeUy is treated with a vegetable acid dissolved in water, a 

 sugar like that of Grape sugar is the resiilt ; that the gvun of Peas 

 placed with oxalic acid in a temperature of 125°, is converted into 

 sv^ar ; that the gum obtained from starch, mixed with the juice of 

 green Grapes, renders it saccharine ; and, finally, that tartaric acid, 

 assisted by heat, produces the same effect ; which is what causes 

 most fruits to become sweet when cooked. (De GandoUe, Phya. Veg., 

 p. 68S. 



