Imbibition

Imbibition — Diffusion Into a Solid

Imbibition is a special case of diffusion in which water is absorbed by solid, specifically colloidal, materials, causing them to swell and increase in volume. The classic examples are the uptake of water by dry seeds and by dry wood.

It still counts as diffusion because water is moving along a water-potential gradient — dry seeds and dry wood start out holding almost no water, so the gradient favouring uptake is very steep, and they absorb water readily. The swelling force this generates, the imbibitional pressure, is surprisingly powerful:

• Historically, people drove dry wooden wedges into cracks in rock and then wetted them — the imbibing wood swelled with enough force to split the rock.
• A germinating seed relies on the very same pressure to physically push its way up through the soil and emerge above ground. …