Plant-Water Relations

Why Water Dominates Plant Physiology

Water is not just one input among many for a plant — it is central to essentially every physiological process, because the protoplasm of a living cell is, at its core, water with countless molecules dissolved in it and particles suspended within it.

How much water a plant actually holds varies enormously:

• A watermelon is over 92% water by weight.
• Most herbaceous (soft-stemmed) plants have only about 10–15% dry matter, meaning roughly 85–90% of their fresh weight is water.
• Even within one plant, woody tissue holds comparatively little water while soft, actively growing tissue holds much more.
• Even a seed that looks bone-dry still holds a small amount of water — without it the seed's tissues could not remain alive. …