Who discovered that and ...how?
I don't know the who.
Or rather, I do. Nice music from time to time.
I know the how better: you remove the foliage from the plant and weigh it. You put it in a nitrogen and oxygen rich atmosphere, no CO2. Then you add a certain mass of water.
Wait a little.
Weigh the leaf. Take the water, weigh that too.
If the leaf has increased weight, it has taken up water. If the mass of water has decreased by the same amount, it's in the foliage.
"But what about the cut site?! That's a huge opening!"
Absolutely! A smart scientist would cover that wound with something that keeps water out.
"Were the scientists who first worked on this very smart?"
No. Not at all, they were curious. So it took possibly 50-100 years to be confirmed.
Nowadays we put carbon isotopes into water, and see where they end up. Not sure if that can be done with things like oxygen or hydrogen, I think it's possible and it's probably been done.
"But water uptake is not the same as drinking!"
Absolutely.
So we do cuttings and put a bunch in water, and a bunch under mist, while never letting any wounds touch the water and see which ones live the longest. It's the misted ones. They take in water, and breathe it out again. That's respiration.
The ones floating in water, take water in but hardly breathe it out again. That's not respiration, that's osmosis.
It depends on how you define drinking of course. One or two beers is drinking in my book, but I know people who say a six pack is drinking and anything less is just refreshing.
