faint lines which appear in the dark portion of the surface are the prints of the threads forming the sack.
Though the effect of the sunlight upon the color of apples is so well known, the nature of the pigment formed and the changes which it may undergo are not well understood. It is apparent from chemical studies that iron is present in its composition and this has led to the belief in some quarters that a soil rich in iron compounds is a factor of prime importance for the production of highly colored fruit. As a matter of fact, iron is also necessary to the production of chlorophyll in the leaves,
Print of a Leaf upon the Surface of an Apple about One Half Natural Size.
and since the ash of the leaves contains a larger proportion of iron than that of the fruit, it seems fair to suppose that soils containing sufficient iron for proper chlorophyll development also have an abundance for the formation of pigment in the fruit.
Even more obscure are the causes which lead to the formation of pigment in certain varieties while it is absent or nearly so in others. While the color is no doubt greatly influenced by heredity, this fact takes us but a short step nearer the solution of the problem. It was formerly held that not only the color but also the form, size and flavor of an apple might be greatly influenced by the variety furnishing the
