How do we know?
↻ One of the pages with a moving picture
A man grew a tree in a pot and weighed the soil.
- Inside a seed is a tiny baby plant, wrapped in a seed coat with a packed lunch of stored food.
- When it gets water, oxygen and the right warmth, water and oxygen soak in through the seed coat.
- The seed coat breaks open. The root comes out first, then the shoot with the stem and leaves.
- The leaves use sunlight, water and carbon dioxide from the air. Carbon from the air builds most of a plant’s dry weight.
Almost 400 years ago, Jan Baptista van Helmont grew a willow in a pot of soil for 5 years. The tree gained 75.4 kg, but the soil lost only 57 g! He guessed the wood came from water.
Today we know most of it comes from carbon in the air.
Even the biggest trees start tiny. General Sherman in Sequoia National Park, California, the world’s largest tree by volume, grew from a seed about the size of an oatmeal flake.
Wow number
1,400 tons The trunk of the General Sherman tree weighs nearly 1,400 tons, about as much as 10 train engines!
Myth or fact?
A tree’s wood is made mostly from soil. Myth. Most of a plant’s dry weight is built from carbon taken from the air.
A seed has a tiny plant with a root, stem and leaves inside. Fact. It waits inside the seed coat until conditions are right.
Think about it
Why do you think the root comes out before the shoot?
Where in the world?
Sequoia National Park, California, USA where General Sherman, the world’s largest tree by volume, grew from a seed about the size of an oatmeal flake — 36.5817° N, 118.7511° W.
Where these facts come from
Every number on page 62, and who measured it
This page tells us the parts of a seed: the seed coat, the baby plant and its food.
Journey to the Center of a Seed — KidsGardening, a group that helps kids learn by gardening
kidsgardening.org/resources/lesson-plans-journey-to-the-center-of-a-seed
We checked it on 31 October 2026
This page tells us what a seed needs to sprout, and that the root comes out first.
Germinating Seeds — West Virginia University Extension
extension.wvu.edu/lawn-gardening-pests/news/2021/02/01/germinating-seeds
We checked it on 31 October 2026
This page tells us that most of a plant's dry weight is carbon from the air.
31.1 Nutritional Requirements of Plants - Biology 2e — OpenStax, free college textbooks from Rice University
openstax.org/books/biology-2e/pages/31-1-nutritional-requirements-of-plants
We checked it on 31 October 2026
This page tells us how big and heavy the General Sherman tree is.
The General Sherman Tree — The U.S. National Park Service
nps.gov/seki/learn/nature/sherman.htm
We checked it on 31 October 2026
This page tells us that giant sequoia seeds are about the size of an oatmeal flake.
Giant Sequoias: From Oatmeal-Sized Seeds to Towering Groves — The U.S. Geological Survey, the government's Earth scientists
usgs.gov/news/giant-sequoias-oatmeal-sized-seeds-towering-groves
We checked it on 31 October 2026
This page tells us about van Helmont's willow tree test.
Carbon fixation – Biological Principles — A biology textbook from Georgia Tech, a science university
bioprinciples.biosci.gatech.edu/09-carbon-fixation
We checked it on 31 October 2026
This page tells us when van Helmont's willow test was published.
Van Helmont's weight balance and the willow experiment (Ortus medicinae) — Stemma Science, a website about the history of science experiments
stemmascience.org/en/node/van_helmont_1648
We checked it on 31 October 2026
This page also tells us when van Helmont's willow test was published.
Jan Baptist van Helmont — Wikipedia, a free online encyclopedia
en.wikipedia.org/wiki/Jan_Baptist_van_Helmont
We checked it on 31 October 2026
Has this changed?
How a seed grows is not going to change.
What changed was our idea of where wood comes from. Van Helmont guessed water, and today we know most of it is carbon from the air.
Words from this page
- seed coat
- The tough skin around a seed.
- shoot
- The part of a baby plant that grows up, with the stem and leaves.
- carbon dioxide
- A gas in the air that plants take in to build themselves.
Try it!
Watch a bean sprout in a bag.
1. Fold a damp paper towel and put it in a clear zip bag with 2 or 3 dry beans. 2. Tape the bag to a sunny window. Keep the towel damp, not soaking. 3. Check every day for a week and draw what you see. (Beans are for growing, not eating!)
What happens: after a few days the seed coats split and a little root pokes out first. Later a green shoot grows up.
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