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“The most important chemical reaction on earth is photosynthesis,” said Robert DeFeo, chief horticulturist for the National Park Service. “We are all parasites upon it.” Essential though plants may be to our survival, Dr. Raven emphasizes that they are a radically different form of organism than are animals. Plants and animals have evolved along separate paths for hundreds of millions of years, ever since single cells began pooling their talents into multicelled beings. “Plants have evolved their multicellularity completely separately from animals, and any direct comparisons between the groups are wrong,” Dr. Raven said. “It’s as if plants evolved on Mars, and animals here.” In addition to their caloric self-sufficiency, plants can be envied for their eternal youthfulness. A plant elongates itself through constant cell growth in two zones of its body, at the very tips of the roots, which grow down into soil or other surface to which the plant clings, and the outer tips of the shoots, from which new leaves, flowers and fruits sprout. Whereas an animal, upon reaching maturity, has almost no young cells left in its body, Dr. Raven said, “in plants the ends of the roots and shoots are always juvenile, always growing, always babies.”
in new york times - science