Extratentacular budding always results in separate polyps, each with its own corallite wall. In the case of bushy corals such as "Acropora", lateral budding from axial polyps form the basis of the trunk and branches. The rate at which a stony coral colony lays down calcium carbonate depends on the species, but some of the branching species can increase in height or length by around a year (about the same rate as human hair grows). Other corals, like the dome and plate species, are more bulky and may only grow per year. The rate of aragonite deposition varies diurnally and seasonally. Examination of cross sections of coral can show bands of deposition indicating annual growth. Like tree rings, these can be used to estimate the age of the coral.