APPLE DISEASES 27 
area; in the case of stippen there is no evidence of such 
structures. 
Bitter-pit, or stippen, is frequently confused with hail marks, 
and bruises of various kinds. In the case of any such injuries, 
however, the skin has the appearance of having been pushed in 
rather than shrunken, and also mechanical injuries often show 
a broken skin, a feature not characteristic of stippen. Scab is 
distinguished as follows: it shows at first as a velvety, then as 
a corky, lesion, not depressed. The various apple-rot lesions 
are not depressed until much larger than stippen-spots. San 
José scale marks are sometimes regarded as bitter-pit lesions, 
but the former does not show the plain depression of the latter. 
Most growers will not mistake other diseases for bitter-pit. 
Cause of stippen. 
Stippen is a non-parasitic disease, one in which the primary 
cause is not certainly known, but one for which all parasitic 
organisms, such as bacteria and fungi, are in no way responsible. 
The common opinion of those who have given some consider- 
ation to this phase of the subject is that the pits result from a 
disturbed water relationship. As to the nature of this disturb- 
ance, however, authorities are not entirely agreed. 
Since every grower has his own opinion in regard to the cause 
of this disease it may be of interest to give some of the theories 
of those who have most carefully investigated it. In order to 
make these theories clear it is first necessary to have clearly in 
mind the general structure of the apple-fruit and the nature of 
the spots. The flesh of the growing apple is made up of rather 
large egg-shaped cells within which the living substance of the 
fruit is enclosed, together with the water and mineral substance 
brought up as food from the roots, and the starch made by the 
leaves and green fruit. As the fruit ripens the starch is con- 
verted into sugar. Passing from the twig into the fruit, by 
way of the fruit stem, are large numbers of sap-tubes which, as 
they enter the base of the fruit, separate, and, branching, permeate 
