How do trees grow straight up, even on a slope? © Getty

How do trees grow straight up, even on a slope?

The only way is up thanks to specialised cells in tree roots and shoots.

Asked by: Te Chase, via email

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Trees (and most other plants) detect gravity using tiny structures within the cells of their roots and shoots called ‘statoliths’, which tell them which way is up (a process known as ‘gravitropism’). These pocket-shaped structures are also responsible for storing the plant’s food (in the form of starch).

Statoliths are drawn by gravity towards the bottom of their cell, telling the tree that this direction is down. The tree responds by growing its roots downwards and shoots upwards. If, however, the tree were blown onto its side, the statoliths would shift and settle against whichever part of the cell was now facing downwards. The tree would then use this information to re-orient itself and continue to grow its shoots vertically.

When trees grow, where does the matter come from? © Getty Images

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