Transpiration is the process that plants go through to release water through their stomata. Stomata are small openings on leaf surfaces. During a dry period, the plant will wilt, with most stomata closed, to conserve as much water as possible. Also, if the drought lasts long, the plant will develop thicker cuticles in its new growth to adapt to the lack of water available, and probably put out smaller leaves–because there are stomata on the leaves, having smaller ones will cut down on the amount of water lost through them.
jvanderlee: thank you for this great answer!
Great answer! One thing I want to clarify though is that wilting itself isn’t an adaptive response to drought.
To understand it you have to know about turgor pressure. Normally plant cells are full of water. So much water that it presses out on their cell walls, the same way hair or helium presses out on a balloon. When a balloon is completely inflated it’s hard to squeeze because there is so much air on the inside pressing out, but if you let a little air out of the balloon, it shrinks and becomes more flexible. The same thing happens to plant cells when they can’t get enough water. They become softer, which results in wilting.
jamesandgiantcorn: thanks for the clarification about wilting. I have another question about this– if wilting is caused by a lack of water pressure in the plant cells, how come over watering plants also can cause them to have a “wilting” appearance? I’m assuming there is a different process occurring– like the cells dying?
That’s a good question. I’m not sure this is always the answer, but often overwatering can actually cause the roots to begin rotting. When that happens, the stem and leaves of the plant aren’t getting enough water, even as the roots are dying from too much. I’ll look into it tomorrow and see if there are also other reasons.
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