Study
Ortus medicinae
van Helmont, J. B.
Ludovicus Elzevirius, Amsterdam, 1648
A willow shoot of known weight was planted in a measured quantity of dried soil in a covered pot and watered for five years, after which the tree and the soil were dried and weighed again.
- Studied in
- Salix
- Sample size
- 1 willow sapling grown in a weighed pot of soil
The willow gained roughly 74 kilograms while the soil lost only about 60 grams. Almost none of the tree had come out of the pot.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Van Helmont concluded that the added mass had come from the water, which was the only substantial input he had supplied.
How NatureHQ reads it
One of the most useful experiments ever performed for a wrong reason. The measurement was excellent and the conclusion was half right: hydrogen in the wood does come from water, but most of the mass is carbon and oxygen from air, which he had no way to weigh and no reason to suspect. The value for a reader is the structure of it — the soil was weighed, and it had not gone anywhere. Everything after that is about identifying which invisible input was responsible, which took another century and a half.
- A single plant with no replication or control.
- Air was not weighed and could not have been, so the actual source of the mass was outside the design.
- Mineral nutrients drawn from the soil are small in mass but not zero, and the balance was too coarse to resolve them well.
The willow, the pot of soil, and the five-year weigh-in
Does a growing tree eat the soil it stands in?
What this study is used for on NatureHQ
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