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Gravity and growth
By C. Cazeau in category FOLLOW-UP
Around 400 million years ago, the first forms of terrestrial life of aquatic origin colonized the continents. These were plants, and they were exposed to much greater mechanical forces on land than in the water. They adapted themselves so that their roots grew in the soil and aerial growth occurred above the ground. In these conditions, wood (and later, bone) had to be rigid enough to withstand breaking, and flexible enough to absorb elastic and plastic energy. Phylogeny and ontogeny therefore had to make them ‘fit’, and adaptable to their mechanical environmental pressures . These pressures constitute signals of utmost importance, affecting morphogenesis and growth, and can be separated into endogenous and exogenous forces. Endogenous forces include muscle forces in animals, and elastic tension or turgidity of stems in plants; external forces consist essentially of gravity in both kingdoms, as well as touch and wind in plants. This gravitational vector, present at the onset of life, is an inevitable and constant parameter of fixed orientation, constituting both an immutable landmark and a factor of physical restriction . Pre-dating all life, it has accompanied phylogenesis through time. The question here is how this vector influences ontogeny.
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