Imbibition in plant seeds*

The mass of plant seeds varies over six orders of magnitude, and water permeation of the dry porous tissue is an essential requirement for germination. However, it is unclear if the imbibition process is similar across the full spectrum of seed sizes, or if variations in their porous structure lead to heterogeneous flow patterns. We describe imbibition in real and artificial plant seeds, using a combination of experiments and theory. In both systems, our experiments demonstrate that liquid permeates the substrate at a rate which decreases gradually over time. Tomographic imaging is used to confirm this by observation of the permeating liquid using an iodine stain. To rationalize the experimental data, we propose a model based on capillary action which predicts the temporal evolution of the radius of the wet front and the seed mass. The depth of the wetting front initially evolves as t^1/2 in accord with the Lucas-Washburn law. At later times, when the sphere is almost completely filled, the front radius scales as (1 − t/t_max)^1/2, where t_max is the time required to complete imbibition. The data obtained on both natural and artificial seeds are compared to the model.