If we are struggling to understand a concept we often find it useful to compare one thing with another. I think this tree metaphor is very useful for understanding all sorts of mysteries about growth and change.
As trees and other plants mature over time, new structures appear. Developments may be obvious, as when flowers or other reproductive structures first appear, or more subtle, like the maturing of xylem or phloem.
BUT – this does not necessarily mean that earlier structures disappear. Indeed they often spread up and out with the branches or down into the ground with the roots…The structures that appear when a tree is a tiny seedling are still present in a huge tree – at the very tips of the branches and roots. (1)
See the full description of tree growth here – (1)http://trees.tennessee.edu/concepts.html
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