Natures wonders: open sesami (Introduction)

by David Turell , Saturday, October 21, 2023, 17:05 (189 days ago) @ David Turell

How it spreads seeds:

https://www.wsj.com/public/resources/documents/5ROSrjoB1ANAAUM9mSdR-WSJNewsPaper-10-21-...

The sesame seeds are neatly lined up inside each compart ment, protected from the world as
they grow.

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In the case of sesame, the plant needs to disperse the fully grown seeds by opening each capsule in a way that will let the seeds blow away on the wind. So the structure of the
capsule has a very specific pattern. Each of its four compartments is made up of a long C-shaped trough, with the seeds on the inside. A compartment wall has three layers: The first two are made of stiff cells full of cellulose microfibrils, but the outer one is quite different, made from a much more open and disorganized collection of soft cells with no stiff microfibrils.

The two inner layers hardly change when they dry out or get wet, but the outer layer is like a soft but strong sponge. When the capsule is growing, that layer is thick and plump because it’s full of water, but as the seeds ripen it starts to dry out. It loses so much water that it shrinks to 30% of its original thickness; it also shrinks asymmetrically. This leaves the whole outer layer in tension, a bowstring primed to fire.

When the tension gets too much— pop!—each compartment pulls away from the others by breaking at the line of weakness where the compartments join, snapping back and outward, away from the center. At the same time, the C-shapes open up, flattening the compartment walls. Seeds can come flying out at this point, or they can wait until the wind picks them up and carries them off. It’s thought that this sudden reveal is the origin of the phrase “Open sesame,” made famous in the story of Ali Baba in “One Thousand and One Nights.”

Comment: Viewed as a purposeful design, there is no way a Darwin theory can explain this irreducibly complex mechanism.