In 1649, Jan Baptista Van Helmont did the first biological experiment in which the ingredients were measured accurately and all changes noted precisely. Van Helmont began by transplanting the shoot of a young willow tree into a large bucket of soil. He weighed the willow and then the soil separately. If the willow tree formed its tissues by absorbing the nutrients from the soil then the soil should lose weight as the plant grew. Van Helmont carefully kept the soil covered so that absolutely nothing could interfere with his experiment.

Naturally, Van Helmont had to water the willow tree or else it wouldn’t grow. He concluded that the water he was adding helped carry the nutrients to the tree and then simply evaporated into the air.

For five years, Van Helmont waited patiently, watching the tree grow until finally he removed it from the pot, shook off all the soil and and weighed the plant. In five years the willow tree had added 164 pounds to its original weight. Then, for the second part of the experiment, Van Helmont dried and weighed the soil. Had it lost 164 pounds to the weight of the tree? No. It had only lost 2 ounces!

From this, Van Helmont concluded that the willow tree drew its nutrients, not from the soil but from water. Accidentally, he made a mistake and said that the material that made up the bark, wood, roots and leaves came from the water he had added over the five years!

The next big important step in the understanding of photosynthesis came in the early 1770’s. Joseph Preistly, the British man who received the recognition of discovering oxygen, found that a piece from a mint plants could restore the air in a container with a burning candle, so that it could be used again. Accidentally, one day, Joseph Preistly placed the candle in a dark corner of his laboratory. Since the mint plant could not photosynthesize, the candle’s flame extinguished. Unfortunately, Mr. Preistly never did really understand that great role which light played in his experiment.

Several years later, in 1979, a Dutch physician, Jan Ingenhousz, wanted to find out whether flowers really did help cure illnesses. After many