The histological similarities and differences between the boron-amenable disorders, internal cork, corky core, and drought spot, and the non-boron-amenable disorder, bitter pit, are presented. Blotchy pit is discussed as a borderline type, since one end of a graded series is similar to internal cork and the other is indistinguishable from bitter pit. On the basis of histology water core is not placed in either of the two groups.Starch retention, in localized or diffuse necrotic areas, is common to both groups of disorders. External papillations occur on the walls of cells in close proximity to the lesions. Abnormal meristematic activities coexist with boron deficiency. These are (1) a cork cambium partially or completely walling off a lesion, (2) massed linear cells, heavily papillated, and (3) reactivated individual cells or groups of cells. All three types of abnormal cells may be present in internal cork and drought spot, but no cork cambium occurs in corky core.