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Jan Baptista van Helmont
He put a willow tree in a pot for five years and observed that the tree had increased in mass but the soil had not lost mass. This led him to conclude that the excess weight of the tree was derived from water. He later conducted another experiment that identified many gases. This would later be researched and linked to photosynthesis. Though he had misconceptions that plants derived nutrients from water, his research played a key role in the discovery of how water affects plant growth. -
John Woodward
To test van Helmont’s theory, Woodward grew mint plants and watered them with different samples of water, such as rainwater, river water, drainage water, and others. He noted that the plants expelled the water through pores in their leaves, accounting for the loss in water mass that van Helmont discovered. -
Stephen Hales
Stephen Hales was considered the father of plant physiology. His research showed that plants derive something from the atmosphere. He observed that the volume of air decreased when a plant was being grown in an enclosed atmosphere. -
Joseph Priestley
Joseph Priestley performed an experiment that proved the existence of oxygen and carbon dioxide, though he did not know it yet. He put a plant and a candle in a sealed container, and lit the candle. He noted that the candle went out almost immediately. He repeated the experiment a month later and found that the candle remained lit for a much longer period of time. Priestley concluded that plants can change the air composition, and somehow restore the air used by the candle. -
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Antoine Lavoisier
Antoine Lavoisier investigated the composition of air and water. Lavoisier sought to replace the “Phlogiston Theory” created by Ancient Greek alchemists and elaborated upon by scientists before Lavoisier’s time. In studying the composition of air, he formed the Oxygen Theory, which accounts for the “dephlogisticated air” that plants give off. -
Jan Ingen-Housz
Jan Ingen-Housz based his experiment on Priestley’s. He too put a plant and a candle in a transparent container. However, he did not light the candle. He let the container sit in the sunlight for two to three days, then covered it for several days. After this period, when he attempted to light the candle, it would not light. This determined that plants require light to survive. -
Jean Senebier
Jean Senebier created an experiment that showed that leaves that were submerged in water without carbon dioxide present did not produce oxygen. He did not coin the terms carbon dioxide and oxygen, calling them instead fixed air and dephlogisticated air, respectively. -
Nicolas de Sassure
Nicolas de Saussure repeated the earlier experiments of keeping plants in enclosed containers. This was, however, after carbon dioxide was named and thus he was able to observe that carbon dioxide is absorbed by plants during photosynthesis, and that it comes from the atmosphere and not the earth, as some earlier scientists believed. -
Julius Robert von Mayer
Julius Robert von Mayer found that the sun is the ultimate source of energy for plants.
He discovered that the absorption of light in plants occurs through a process called photosynthesis. -
Julius von Sachs
Sachs showed that the green pigment in leaves is called chlorophyll, and he explored the role it takes in photosynthesis. He also studied the role of light on the growth of starch, as well as the presence and purpose of starch in plants.