Botanical term: “Imbibe”. Most seeds can remain dry-dormant for long periods of time. When they take in moisture to capacity, they are said to “imbibe” it, or to “become imbibed”. Some seeds, like the beans used for food, noticeably swell. Others, like tree seeds such as apples and maples, do not look much different. In these cases, the main change is internal texture. The plant embryo, which was hard and brittle when dry, becomes leathery or soft.
The state of “being imbibed” with moisture is distinct from simply “wetted”. Seeds with an impervious coat may not become imbibed, even when soaked in water. On the other hand, many seeds will become fully imbibed when placed in soil that seems scarcely moist to the touch.