Seeds Drill Into Soil

light brown wheat stalks fill the frame, sticking all directions with a blurry background

Biological Strategy

Wild wheat

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Image: Hans Braxmeier / Pixabay / Free non-commercial use

Move in/on Solids

To obtain needed resources or escape predators, some living systems must move on solid substances, some must move within them, and others must do both. Solids vary in their form; they can be soft or porous like leaves, sand, skin, and snow, or hard like rock, ice, or tree bark. Movement can involve a whole living system, such as an ostrich running across the ground or an earthworm burrowing through the soil. It can also involve just part of a living system, such as a mosquito poking its mouthparts into skin. Solids vary in smoothness, stickiness, moisture content, density, etc, each of which presents different challenges. As a result, living systems have adaptations to meet one, and sometimes multiple, challenges. For example, some insects must be able to hold onto both rough and slippery leaf surfaces due to the diversity in their environment.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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The awn of wild wheat grass drills the seed into the soil by absorbing moisture, causing the awn to unwind.

“The dispersal unit of wild wheat [Triticum turgidum] bears two pronounced awns that balance the unit as it falls. We discovered that the awns are also able to propel the seeds on and into the ground. The arrangement of fibrils causes bending of the awns with changes in humidity. Silicified hairs that cover the awns allow propulsion of the unit only in the direction of the seeds. This suggests that the dead tissue is analogous to a motor. Fueled by the daily humidity cycle, the awns induce the motility required for seed dispersal.” (Elbaum et al. 2007:884)

Last Updated September 14, 2016

References

Web page

Needle and thread grass

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Reference

Journal article

The Role of Wheat Awns in the Seed Dispersal Unit

Science | 10/05/2007 | R. Elbaum, L. Zaltzman, I. Burgert, P. Fratzl

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