Stems Resist Buckling

close up photograph of green and purple veined plant

Biological Strategy

Plants

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Manage Compression

When a living system is under compression, there is a force pushing on it, like a chair with a person sitting on it. When evenly applied to all sides of a living system, compression results in decreased volume. When applied on two sides, it results in deformation, such as when pushing on two sides of a balloon. This deformation can be temporary or permanent. Because living systems must retain their most efficient form, they must ensure that any deformation is temporary. Managing compression also provides an opportunity to lessen the effects of other forces. Living systems have strategies to help prevent compression or recover from it, while maintaining function. For example, African elephant adults weigh from 4,700 to 6,048 kilograms. Because they must hold all of that weight on their four feet, the tissues of their feet have features that enable compression to absorb and distribute forces.

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Prevent Buckling

When a living system undergoes compression to the extent that it causes structural damage, it results in buckling. For example, if a person pushes down on the top or the side of a paper cup, the cup’s wall will eventually give way, or buckle. Although a living system could add material to strengthen a structure, this requires expending precious energy. Instead, it must use energy and materials conservatively to avoid buckling, strengthening structures through careful placement of materials to resist, absorb, or deflect compressive forces. For example, instead of one long, tubular stem, some plants like bamboo have stronger nodes scattered along their stems. When compressed, these nodes keep the round stems from taking on an oval shape that weakens the structure and could result in buckling.

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Plants

Phylum Plantae (“plants”): Angiosperms, gymnosperms, green algae, and more

Plants have evolved by using special structures within their cells to harness energy directly from sunlight. There are currently over 350,000 known species of plants which include angiosperms (flowering trees and plants), gymnosperms (conifers, Gingkos, and others), ferns, hornworts, liverworts, mosses, and green algae. While most get energy through the process of photosynthesis, some are partially carnivores, feeding on the bodies of insects, and others are plant parasites, feeding entirely off of other plants. Plants reproduce through fruits, seeds, spores, and even asexually. They evolved around 500 million years ago and can now be found on every continent worldwide.

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The stems of many plants resist buckling using low-density foam cores.

Image: Louisa Howard, Charles Daghlian, Dartmouth Electron Microscope Facility /

Scanning electron microscope image of x-section through Oryza sativa [Rice] stem, showing vascular bundles arranged in two rings and central pore(usually filled with mucilage, but collapsed in this image).

Image: Louisa Howard, Charles Daghlian, Dartmouth Electron Microscope Facility /

Scanning electron microscope image of Oryza sativa [Rice] stem. High magnification of Oryza stem 1 image, showing a closer view of vascular bundles and cortex.

Image: Louisa Howard, Charles Daghlian, Dartmouth Electron Microscope Facility /

Scanning electron microscope image of longitudinal section of Oryza sativa [Rice] stem. Image shows cuts through the vascular cells and cortex cells. Starch granules are visible inside vascular cells and chloroplasts are visible inside cortex cells.

“Anyone who has squashed an empty metal can knows about the second form of buckling; it’s called ‘local buckling’ or ‘Brazier buckling…Local buckling does occur in biological columns–it’s certainly involved in the lodging of slender crop plants in wind storms, and it can be deliberately induced in any dandelion stem. A low-density foam core reduces susceptibility, and many plants (but not dandelions!) have such cores.” (Vogel 2003:378)

Last Updated September 14, 2016

References

Book

Comparative Biomechanics: Life's Physical World, Second Edition

17/06/2013 | Steven Vogel

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