Hair follicles do not produce hairs continuously; growing phases alternate with periods of rest.In association with this alternation,follicle and shaft pass through a complex series of morphological change which is referred to as the hair cycle.During the growth phase,called the anagen phase,the follicle penetrats deep into the dermis; sections through its deepest portions show complex maturation patterns of cells as the various regions of the shaft are formed.
Cross section of a hailstone,photographed under polarized light,showing typical alternate growth layers of clear and opaque ice. This hailstone,which fell near coffeyville,is, in September 1970, is the largest ever in united state.