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Table 1. Historical Context of Helmont's Willow Experiment: Douglas Allchin's Fabrications versus Reality

Allchin (2002) Fabrications Reality Based Mainly on Literature Review in Hershey (2003)
"Jean Baptiste van Helmont, a Dutch physician from the early 16th century." Helmont (1579-1644) was born in Brussels, Belgium so was Belgian (Pagel 1972, 1982). Helmont was not even alive in the early 16th century.
"Concerns about distilled water in the context of an experiment done centuries before anyone understood the concept are grossly misplaced and distort the process of science." Helmont said "But I moystened the Earthen Vessel with Rain-water, or distilled water." (Helmont 1662). His use of distilled water was an important part of his experiment because he understood that less pure water sources would have added dry weight to his soil. The crux of his experiment was to measure the change in dry weight of his 200 pounds of soil to determine if the plant gained weight from the soil (Helmont 1662). Helmont even went to the trouble and expense of covering the lid of the pot with a tin-coated iron lid to keep out dust (Helmont 1662). Distillation was in use hundreds of years before Helmont was born and was a standard technique for alchemists such as Helmont (Multhauf 1956).
Carbon dioxide was "a substance wholly outside his (Helmont's) conception" Helmont coined the term gas and described several sources of carbon dioxide gas, which he called gas sylvestre, including the bubbles in wine, belches and in the gas that accumulated in mines (Leicester and Klickstein 1963, Pagel 1972). He experimentally determined that when he burned 62 pounds of oak charcoal, it produced 61 pounds of carbon dioxide gas and 1 pound of ash (Leicester and Klickstein 1963).
"Helmont's experiment was well designed and interpreted appropriately in the context of its own time." Helmont ignored the well-known fact that plants contained large amounts of water so he misdesigned the experiment to measure soil dry weight but plant fresh weight (Krikorian and Steward 1968). He should have measured dry weight for both. The metal lid with many holes that covered his pot would not have kept out dust as Helmont proposed. The dust would have simply accumulated on the lid and been washed into the pot when it rained (Hershey 2003). Helmont's conclusion ignored his data that two ounces of soil were missing, which indicated that the plant may require a tiny amount of soil. Helmont did not keep track of the water added to the pot so had no data to show that enough water had been added to the pot to account for the gain in plant weight. Helmont ignored his data that burning 62 pounds of oak charcoal produced 61 pounds of carbon dioxide and one pound of ash. Helmont ignored the ancient knowledge (Tisdale and Nelson 1975) that crop yield would decline when crops were grown in the same field for many years unless manure was added.
"We might even credit van Helmont for his experimental strategy in isolating the relevant soil system within the boundaries of a pot. " The consensus of modern historians is that Helmont got the idea for his experiment from Nicolaus of Cusa's 1450 book, which described a virtually identical thought experiment (Hoff 1964, Howe 1965, Krikorian and Steward 1968, Pagel 1982). Trees, especially oranges, were commonly grown in pots in Helmont's era and overwintered in caves or orangeries (Muijzenberg 1980). Plants have been grown in pots for over 3,000 years (Baker 1957).
"Helmont was also probably well aware that plants do not grow outside soil. There was certainly no existing evidence then to suggest that the substrate of soil was not relevant in some respect." Sir Francis Bacon (1627) described his experiments that involved growth of terrestrial plants in water. Herbals of Helmont's era, such as Gerard (1633) described free-floating aquatic plants such as "ducks meate" (Lemna spp.) or "frogge-bit" (Hydrocharis morsus-ranae). Such plants were common in Europe, and as a physician, Helmont studied medicinal plants (Pagel 1982). Therefore it is likely that Helmont knew of the existence of aquatic plants.
"He even buried his pot in the earth, as if the location was a significant parameter to keep constant." No one knows why Helmont sunk his pot in the ground because Helmont did not say. The most logical reason was to prevent the wind from toppling the pot and spilling the soil, which would have ruined the experiment (Hershey 1991). Gerard (1633) has a drawing of a planted pot sunk in the ground so Helmont was not the originator of the technique.
"This pair of examples is historically outlandish. Van Helmont is both praised and ridiculed as a scientist in the same text. He is both hero and fool." Helmont was considered both hero and fool in his own era because he had many mystical beliefs that were considered bizarre even in his lifetime. Even Robert Boyle, who admired Helmont's scientific work, distanced himself from Helmont because of Helmont's "extravagencies" and "untruths" (Walton 1980). Helmont's "combination of mysticism, magic, alchemy, and new science irritated even his contemporaries" (Heinecke, 1995).
"To assess his hypothesis about the role of water, he should have grown the willow hydroponically - that is, in water alone. And he should have used distilled water, so as to exclude the role of minerals in the water." The term "hydroponics" was not introduced until 1937 by William Frederick Gericke (1937) so represents an anachronism when discussing Helmont's 1648 experiment. It does not maintain the proper historical context that Allchin (2000, 2002) considered so important. Hershey (1991) did not use the term. Allchin (2000, 2002) also misdefined hydroponics. It uses mineral nutrient solutions, not just water.

Literature Cited

Allchin, D. 2002. How not to teach history in science. The Pantaneto Forum. July. (This is a slightly different, online-only version of Allchin 2000).

Allchin, D. 2000. How not to teach historical cases in science. Journal of College Science Teaching. 30:33-37.

Bacon, F. 1627. Sylva Sylvarum. London: J. Haviland.

Baker, K.F. 1957. The UC System for Growing Healthy Container-Grown Plants. (University of California Agricultural Experiment Station Manual 23). Berkeley, CA: University of California.

Gerard, J. 1633. The Herbal or General History of Plants. NewYork: Dover.

Gericke, W.F. 1937. Hydroponics - Crop production in liquid media. Science. 85, 177-178.

Heinecke, B. 1995. The mysticism and science of Johann Baptista van Helmont (1579-1644). Ambix. 42(2),65-78.

Helmont, J.B. van. 1662. Oriatrike or Physick Refined. London: Lodowick Loyd. (translated by John Chandler).

Hershey, D.R. 2003. Misconceptions about Helmont's willow experiment. Plant Science Bulletin 49:78-84.

Hershey, D.R. 1991. Digging deeper into Helmont's famous willow tree experiment. American Biology Teacher 53:458-460.

Hoff, H.E. 1964. Nicolaus of Cusa, van Helmont, and Boyle: The first experiment of the renaissance in quantitative biology and medicine. Journal of the History of Medicine and Allied Sciences, 19, 99-117.

Howe, H.M. 1965. A root of van Helmont's tree. ISIS, 56, 408-419.

Krikorian, A.D. and Steward, F.C. 1968. Water and solutes in plant nutrition: With special reference to van Helmont and Nicholas of Cusa. BioScience, 18, 286-292.

Leicester, H.M. and Klickstein, H.S. 1963. A Source Book in Chemistry 1400-1900. Cambridge MA: Harvard University Press.

Muijzenberg, E.W.B. van den. 1980. A History of Greenhouses.Wageningen. The Netherlands: Institute for Agricultural Engineering.

Multhauf, R. 1956. The significance of distillation in Renaissance medical chemistry. Bulletin of the History of Medicine, 30, 329-346.

Pagel, W. 1982. Joan Baptista van Helmont, reformer of science and medicine. New York: Cambridge University Press.

Pagel, W. 1972. Helmont, Johannes (Joan) Baptista van. pp. 253-259, vol. 6. IN: Gillespie, C.C. (ed.). Dictionary of Scientific Biography. New York: Scribner.

Tisdale, S.L. and Nelson, W.L. 1975. Soil Fertility and Fertilizers. New York: Macmillan.

Walton, M.T. 1980. Boyle and Newton on the transmutation of water and air, from the root of Helmont's tree. Ambix, 27(1),11-18.