14 DAY TRIAL // Many grasses have very peculiar seed dispenser mechanisms, mostly on account of the fact that they are rather small themselves. As a result, they have to ensure the best rate of survival for their offspring. Over the course of millions of years, these plants evolved to create seeds that are equipped with various types of protrusions, which ensure that the seeds are driven into the ground each day. In other words, most hulls on these seeds are completed with bristle-like projections called awns, which in turn are covered with tiny barbs, all of which are pointing away from the seed.
What this does for the seed seems useless until you take into account the fact that the ground is swelling and compressing each day, as humidity is either added or removed from the soil. When a seed lands with its tip pointed downwards, it's only able to penetrate the ground over a short distance. However, if they fall in the correct position, as in if they remain vertical, each time the ground swells or compresses, the tiny barbs on their awns ensure that they are driven a small length further down into the soil. Over the course of a few days, the seeds reach the proper depth, and begin their development.
This effect is one of the main reasons why these seeds are so much trouble to get rid of when they get trapped in the hair or skin of animals. When they enter nostrils, ear canals, or other soft tissue on the beasts' bodies, they tend to lodge themselves in there, and hold on with a firm grip, LiveScience informs. Despite knowing about this mechanism for many years, experts continue to conduct investigations into how the seeds act on whatever surface they come across, only to be able to further advance downwards, and benefit from all the spoils of the underground.
Researchers from the Harvard University, led by expert Igor M. Kulic, focused their efforts on understanding how the foxtail grass Hordeum murinum works. They placed seeds on various shaking surfaces, including paper, fabric, fur, rubber, and others. They noticed that the awns always moved “seedward,” making up for highly-effective ratchets. Kulic even designed a mathematical model of the mechanical system, saying it is “nature's most efficient ratchet.” Further details of the research appear in the latest issue of the scientific journal Proceedings of the Royal Society B.