Contribution to the History of Photosynthesis: Charles Barnes and Conway MacMillan

Charles Barnes (1858-1910) and Conway MacMillan (1867-1929).

Charles Reid Barnes and MacMillan were responsible for the term “photosynthesis”.

Prof. Barnes, an American botanist, was born in Madison, Indiana in 1858.

He acquired a degree from Hanover College in 1877 and then studied at Harvard University.

From 1882 to 1887, he taught botany at Purdue University after which he went to the University of Wisconsin.

Beginning in 1898, he was with the University of Chicago as a professor of plant physiology (Purdue University 2011).

Prof. Conway MacMillan was likewise an American botanist.

He became the first chair of the Department of Botany of the University of Minnesota which position he held until 1907.

The department was established in 1889 (University of Minnesota 2006).

In August 1893, the Botanical Section of the American Association for the Advancement of Science held a meeting in Madison, Wisconsin.

In this meeting, Barnes read a paper in which he proposed the use of the term photosyntax and, as an alternative, photosynthesis, for the biosynthetic, light-dependent process in green plants by which carbon dioxide is reduced to organic matter.

This paper was published in 1893 in the Botanical Gazette (Barnes CR. 1893. On the food of green plants. Bot. Gaz. 18:403-411, cited by Gest 2002).

Accordingly, Barnes defined photosyntax as the “synthesis of complex carbon compounds out of carbonic acid, in the presence of chlorophyll, under the action of light.”

He argued that the various terms used to refer to the process such as ‘assimilation’, ‘assimilation proper’, and ‘assimilation of carbon’ are inappropriate and confusing.

He noted that “assimilation has long been used in animal physiology to designate the appropriation of digested food by the different tissues and its conversion into the substances of those tissues.

However, in that same Madison meeting, Prof. Conway MacMillan expressed a preference for the word ‘photosynthesis’ which Charles Barnes himself proposed as an alternative term.

For some reason, Barnes rejected MacMillan’s suggestion and at the same time emphasized his preference for the word ‘photosyntax’ in a paper published in 1896.

But in his ‘So-called “Assimilation” published in 1898, he wrote: “It is not important whether photosyntax or photosynthesis, or some other word, finally comes into general use to describe the manufacture of carbohydrates by green tissues under the action of light.”

Photosynthesis has since become the accepted term.

In 1963, Ruben Kamen (1913-1943) suggested the following definition of photosynthesis that applies to both oxygenic (O2 is evolved) and anoxygenic (no O2 is evolved) photosynthesis:

“Photosynthesis is a series of processes in which electromagnetic energy is converted to chemical-free energy which can be used for biosynthesis.”

Thirty years later in a 1993 paper, Howard Gest of the Indiana University proposed the following revised definition:

Photosynthesis is a series of processes in which electromagnetic energy is converted to chemical energy used for biosynthesis of organic cell materials; a photosynthetic organism is one in which a major fraction of the energy required for cellular synthesis is supplied by light” (Gest 2002).

Note: The list of Literature Cited is on the Mainpage.

Further reading: What is Photosynthesis

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Ben Bareja

Ben Bareja, the owner-founder-webmaster of This website was conceptualized primarily to serve as an e-library for reference purposes on the principles and practices in crop science, including basic botany. Read more here

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