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There's a genus of plants known as Typha, or cattail. They have seeds like of dandelion, that form thick heads. Such a head may be cut off from the plant and be used for, say, decorative purpose, but when the spring comes, seeds will spread out their 'hairs' and fly away. It looks like an absolutely dry piece of plant - no life in it - suddenly gets alive.

I suggest that it may be a daytime prolongation of a that causes it to spread seeds, but I wonder if anyone knows what sort of cellular/biochemical mechanics is at work here.

Cattail head spread its seeds

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According to LeRoy G. Holm's World Weeds: Natural Histories and Distribution:

Seeds are protected from germinating in the stalk by the swelling of the pistillodes that are distributed throughout the inflorescence. In humid conditions, they swell and keep the spike intact. They can swell 15 to 20% in 15 min in 100% relative humidity. Upon drying, the pistillodes shrivel, air again reaches the seed, and the perianth hairs spread. Their collective pressure causes the inflorescence to burst, releasing the fruits to the air. If they fall on water, the hairs close and the pericarp releases the seed which then sinks.

So it's all about the humidity!

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  • $\begingroup$ So the plant should get completely dry to let its seeds free. Wow. $\endgroup$ – Usurer Mar 27 '18 at 10:34

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