Heartwood formation is a genetically programmed process that happens spontaneously. Some uncertainty exists as as to if the wooden dies throughout heartwood formation, as it can still chemically react to decay organisms, but solely once. In the tree a knot is both the base of a facet department or a dormant bud. Where the variations between the 4 seasons are distinct, e.g. If the distinctiveness between seasons is annual (as is the case in equatorial regions, e.g. Singapore), these progress rings are referred to as annual rings. Where there might be little seasonal difference growth rings are prone to be indistinct or absent.