A mature tree's primary growth is found b. in its developing leaves on young branches.
Young branches where leaves are developing are where an ancient tree's main growth takes place. Plants would continue to develop as long as their environment contained the nutrients they needed to do so because they are organisms with indeterminate growth.
In an ancient tree, the apical meristems at the ends of stems and the tips of roots still experience primary growth or lengthening. The lateral roots of an elderly tree also experience main growth. They still produce new leaves on immature branches due to the apical meristems found in their apical buds.
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