Central to the success of vascular plants is their ability to pull water from the soil. But to pull water from the soil, these plants need roots, and these roots need to be able to grow belowground. Without sunlight to power photosynthesis, growing roots depend on carbohydrates imported from aboveground. Thus, vascular plants develop a second transport tissue, the phloem, capable of moving carbohydrates efficiently across the entire length of the plant. The phloem supports not only the growth of roots, but also the development of non-photosynthetic organs such as reproductive structures and stems.

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