When it’s dry outside, pine cones open up to disperse seed. Pine cones are the most common example of a hygromorph, which changes shape based on humidity levels. The cells inside the cone are dead, and the triggered response is completely automatic. When they’re dry, a small section of the outer layer of the scale near the mid-rib shrinks, pulling the whole scale back and opening it up. When it’s damp, the moisture causes the layer to expand in such a way that it closes the cone.
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