138 ELEMENTARY AGRICULTURAL CHEMISTRY 



tend to favour the growth of leaves and twigs rather than 

 fruit. Fruits are, as a rule, very rich in w^ater, contain sugar 

 and generally some vegetable acid, to which their characteristic 

 taste is partly due. We can only very briefly consider the 

 chemical character of some of the principal typical fruits. 



Apples {Pf/rus malus). — An immense number of varieties 

 of this fruit are known, differing very much in size, shape, 

 colour, and flavour. Doubtless their composition will also 

 vary greatly. They usually contain about 85 per cent. 

 of water, about 12 per cent, of carbohydrates (chiefly sugar), 

 about 0*4 per cent, of ash, 1 per cent, of crude fibre, and 0*2 

 per cent, of albuminoids. The acidity is due to malic acid 

 ^HgC^H/ ) V which may amount to from 0*2 to 1 per cent, of 

 the juice. The diflference in " sweetness " of different apples 

 is mainly due to the propoition of malic acid present. The 

 sugar present is partly cane sugar (sucrose), partly invert 

 sugar, which is a mixture of dextrose and levulose. In green, 

 immature apples starch is found, sometimes to the extent of 

 5 per cent., but as the fruit ripens the starch disappears and 

 the sugars increase. Cellulose is present to the extent of 

 about 1 per cent., pentosans up to about 5 per cent., and 

 pectin, or perhaps more accurately pectose, from 0*2 to 0-6 

 per cent. The gelatinising property of pectin is of importance 

 in the preparation of apple jelly. 



The following analyses of American Baldwin apples will 

 show the changes which occur during ripening : 



