A History of the Ecological Sciences, Part 28: Plant Growth Studies During the 1700s

Abstract

During the 1600s naturalists made significant progress in describing and illustrating plant anatomy. Development of microscopes both stimulated and aided such studies. Foremost contributors were Marcello Malpighi (Adelmann 1966, I:384–417, 423–426, Belloni 1974), and Nehemiah Grew (Metcalfe 1972, LeFanu 1990), and to a lesser extent, Antoni van Leeuwenhoek (Egerton 2006a:54–55). They found minute pores (stomata) that seemed to indicate that plants interact with the air (Nash 1957:335). Achievements in plant physiology during the 1600s were more modest. Botanical researchers had established that over time a tree seedling in a tub with a weighed amount of dirt gains weight if watered regularly (apparently showing that wood came from water), and that cuttings from some plants gain weight if their stems are left in water (Egerton 2004). In 1724, Richard Bradley supported the hunch of two correspondents that plants draw nourishment from the air, and Jethro Tull ridiculed him for it (Egerton 2006b:120). A detailed documentary history by Leonard K. Nash, Plants and the Atmosphere 1957, includes a helpful flow chart of ideas and discoveries, 1650–1804, and Oliver Morton's book on photosynthesis and the economy of nature has a concise history of discoveries during the 1700s (2007:325–343). Stephen Hales (1677–1761) is generally considered the founder of plant physiology (Clark-Kennedy 1929, Nash 1957:336–343, Guerlac 1972, Alan and Schofield 1980, Morton 1981:246–253, Harré 1983:52–58, Allan 2004), which relegates his predecessors to the status of precursors. He went to Cambridge University in 1696 and studied to become a clergyman. His interest in science was awakened in 1703 after William Stukeley arrived. Although Hales was 10 years older than Stukeley, they became close friends. Together they attended lectures and demonstrations in science, conducted various experiments, and went on field trips around Cambridge to collect plants, using John Ray's Cambridge flora (1660). Stukeley's map of where they collected survives and is reproduced, as is his portrait, by Clark-Kennedy (1929: Plates 3, 5). About 1706 Hales experimented on blood pressure in dogs. Yet his new scientific interests did not divert him from becoming a clergyman in 1709, at Teddington, a village on the Thames River (Clark-Kennedy 1929: Plate 14). In 1712–1713 he resumed experiments on blood pressure, and in 1718 he and Stukeley were elected fellows of the Royal Society of London. I cut off all the leaves of this plant, and laid them in five several parcels, according to their several sizes, and then measured the surface of a leaf of each parcel, by laying over it a large lattice made with threads, in which the little squares were ¼ of an inch each; by numbering of which I had the surface of the leaves in square inches, which multiplied by the number of leaves in the corresponding parcels, gave me the area of all the leaves; by which means I found the surface of the whole plant, above ground, to be equal to 5616 square inches, or 39 square feet. He then measured the length of the root system. There were eight main roots, 15 inches long. He selected one of them with lateral rootlets attached and weighed it; then he measured its length plus the length of all rootlets; then he weighed the other seven main roots with rootlets attached and found that “the sum of the length of all the roots to be no less than 1448 feet. Next, he used a complex calculation to determine the surface area of all the roots, which was 15.8 square feet, which was three-eighths of the aboveground surface area. Finally, he measured the velocity of water movement in that plant, given the fact that it perspired 20 ounces of water in a 12-hour day. That was not the end of his experiment, but this summary and quotation illustrate his thoroughness. He found that his sunflower (before he dismantled it) “perspired”(now transpired) an average 1 lb., 4 oz. of water in 12 hours. His discovery of transpiration was of fundamental importance. Was the water lost merely evaporated, or was there also root pressure pushing water up the stem? To find out (in Chapter 3), in experiment 34, on 30 March at 3 pm, he cut off a grapevine stalk 7 inches above the ground and attached a glass tube to it (the joint sealed with melted beeswax and turpentine). There was no action, so he filled the tube 2 feet high with water, which was absorbed by the stem down to 3 inches of the bottom by 8 pm. During the night, “it rained a small shower”(Hales 1961:57). At 6:30 am the water in the tube was 3 inches higher than it had been at 8 pm. The temperature was 43° (Fahrenheit). And so on, through experiment 39 and figures 17–20, to demonstrate the existence of root pressure. Hales not only made important discoveries about water relations in plants, he also investigated plant interactions with air (Chapter 5). He acknowledged that both Grew and Malpighi had thought that air is carried in the largest vessels of wood. Perhaps that is why Hales studied stems rather than leaves. The vacuum pump had been developed in the 1600s and he used one in these experiments. Exactly what air is had not yet been determined, and so he did not explore the roles of oxygen and carbon dioxide. One historian of chemistry commented (Partington 1957:91) [Hales'] chemical work—probably under Newton's influence—is entirely quantitative, and is a good example of the poor results obtained when the qualitative chemical characters of the substances investigated are neglected, but his experiments inspired both Black and Priestley. This is more concise than Partington's later conclusion (1962:112–122). Like many a pioneering scientist, Hales had to invent not only experimental techniques, but also experimental equipment. He illustrated his experiments, described his equipment, and explained how to duplicate his experiments. His studies of airs may have arisen from his plant research, but those studies were not limited to plants. The vacuum pump was helpful, but insufficient. He therefore invented two versions of a pneumatic trough (Fig. 3). Hale's book was widely read and appreciated. Hale's pneumatic troughs; his figures 33 and 38 from Plates 15 and 17, respectively; r--r in fig. 38 is an “iron retort” made from a gun barrel in which one end was melted shut. Buffon translated it into French (1735) and others translated it into German (1747) and Italian (1750). His investigative techniques and instruments helped stimulate a chemical revolution in the second half of the 1700s. Previously, we saw that John Ray discussed tree ring growth in 1660 and explained that the side of a tree facing the equator grows faster than the opposite side (Egerton 2005:302). On 29 April 1749 Carl Linnaeus (Egerton 2007a) departed on his last exploration, to Skåne in southwestern Sweden. Just before reaching Kristianstad, he saw a recently-cut oak and marked the tree rings that were especially narrow and especially broad. Later, he consulted meteorological records and established that the narrow rings correlated with cool summers and the broad rings with warm summers (Linnaeus 1751:68–69, Caddy 1886–1887, II:356, Blunt 1971:196). This was a beginning of dendrochronology, though later developments were not indebted to these observations published in Swedish. In 1754 a prominent Geneva naturalist, Charles Bonnet (1720–1793) published a book on the function of leaves in plants. His fame rests primarily on his demonstration of parthenogenesis in aphid, but after his eyesight declined, he shifted his research to this topic (Bonnet 1948:146–151). In a biographical article, a fellow Swiss, P. E. Pilet, claimed (1970:286) In the Researches, Bonnet grouped five memoirs, all of which were of prime importance for plant biology: He precisely described the characteristics of the nutrition of leaves and of their transpiratory phenomena. However, a historian of photosynthesis (Nash 1957: chart at 362) concedes only that Bonnet confirmed Hales' opinion that plants have an important interaction with air, and that Bonnet made a significant observation which he misinterpreted. Recent historians of Geneva botany (Naef 1987:340–341) and general botany (Morton 1981:359, note 70) agree with Nash's assessment of Bonnet's work on plant growth. Joseph Black (1728–1799) also benefited from Hales' book. He was the son of a Scottish wine merchant who lived in Bordeaux. In 1740 he went to school in Belfast, and about 1744 he entered the University of Glasgow and became the student assistant to the professor of chemistry. In 1752 he transferred to the University of Edinburgh, where he earned an M.D. degree in 1754 (Partington 1962:130–143, Ihde 1964:35–38, Guerlac 1970). His Latin dissertation was on a chemical subject, the effect of alkaline substances to relieve acid indigestion. After further experiments, he published his most important work: Experiments Upon Magnesia Alba, Quicklime, and Some Other Alcaline Substances (Black 1756, partly reprinted by Leicester and Klickstein 1952:81–91). The most important aspect of this research was an incidental discovery. He found a component of air he called “fixed air” (carbon dioxide), which he could identify by a lime water (aqueous calcium hydroxide) test which caused a white precipitate (calcium carbonate). He also found from experiments on birds and small mammals that fixed air did not support life or even the flame of a candle. Black's other important discoveries concern heat and are not relevant here, though of indirect ecological importance—latent heat and specific heat. Black's demonstration that ordinary air contained a particular kind of air that could be identified opened a door to the search for other kinds of air, and two other Englishmen soon walked through it. Henry Cavendish (1731–1810) was the son of Lord Charles Cavendish, who himself conducted important research on heat, electricity, and magnetism. The son inherited wealth and devoted his life to scientific research (Jungnickel and McCormmach 1996, McCormmach 1971, 2004). He identified “inflammable air” (hydrogen) in 1766 (partly reprinted by Leicester and Klickstein 1952:134–142), which he thought might be the principle of fire, “phlogiston” (Partington 1962:302–362, Ihde 1964:38–40). Phlogiston was the vague “flammable principle,” really a theory of combustion, that had grown uncritically since Georg Ernst Stahl (c.1660–1734), an influential physician–chemist (Partington 1961:653–686, L. S. King 1975, Teich 1982:363–368) had expounded it in his textbook, Fundamenta Chymicae (1723). A candle, for example, gives off phlogiston when it burns; if it burns in an enclosed space, it goes out when the air is saturated with phlogiston. Cavendish's most important discovery was the composition of water (1784; reprinted in Leicester and Klickstein 1952:142–153). In contrast to Cavendish, Joseph Priestley (1733–1804) was from a working-class family, but after his mother died, he lived with a childless aunt who was well off and paid for his education in a dissenting academy (Schofield 1997, Freimarck 1999, Freimarck 2004a, b). This observation led me to conclude, that plants, instead of affecting the air in the same manner with animal respiration, reverse the effects of breathing, and tend to keep the atmosphere sweet and wholesome, when it is become noxious, in consequence of animals living and breathing, or dying and putrefying in it. That the vegetable creation should restore the air which is spoiled by the animal part of it, looks like a rational system, and seems to be of a piece with the rest [of how nature works]. Thus fire purifies water…by distillation, when it raises it in vapours, and lets it fall in rain; and further still by filtration, when, keeping it fluid, it suffers that rain to percolate the earth. We knew before, that putrid animal substances were converted into sweet vegetables, when mixed with the earth, and applied as manure; and now, it seems, that the same putrid substances, mixed with the air, have a similar effect. The strong thriving state of your mint in putrid air seems to shew that the air is mended by taking something from it, and not by adding to it. Franklin hoped this new discovery would “give some check to the rage of destroying trees that grow near houses…” We now know, of course, that Franklin was only half right in concluding that mint mended the air by taking something from it (CO2), and not by adding to it, since a photosynthesizing plant does add oxygen to the air. Priestley further discovered (1773:217–218) that both plants and mice die in nitrous air. Priestley's early experiments led to his being awarded the Royal Society's Copley medal in 1773. The president of the Royal Society, his friend Sir John Pringle, spoke at the presentation, and in doing so explained that winds take vitiated air to plants “for our relief, and for their nourishment” (Pringle 1774). Pringle's speech was published for a wider audience than read Priestley's scientific paper, and it publicized a new dimension to the balance of nature concept: air exhaled by animals is poisonous to other animals but stimulates plants, which, in turn, produce air that is good for animals. Many of Priestley's experiments were collected into two works: Experiments and Observations on Different Kinds of Airs (three volumes, 1774–1777) and another three volumes under a similar title in 1779–1786. Priestley's most famous discovery was of “dephlogisticated air” (oxygen), which he collected on 1 August 1774 by heating mercuric oxide hot enough to separate the elements, and published his discovery in 1775 (Conant 1950:34–48, Leicester and Klickstein 1952:112–122, Partington 1962:256–262). In spring and summer of 1778 Priestley conducted more experiments on plants that continued to give him mixed results, but he finally realized that dephlogisticated air was only produced by plants in sunlight; merely providing heat in the dark did not stimulate plants to purify air (quoted in Nash 1952:366). This research, published in 1779, still contained some confusion and so was not definitive (partly reprinted in Leicester and Klickstein 1952:122–125, Nash 1957:358–369). His final report on his experiments on plant growth (Priestley 1790:247–347) cleared up some of his confusion, but since he never gave up the phlogiston theory, others who did give it up soon gained a better understanding than his (Teich 1982:368–373). The French Revolution began in 1789, and as it progressed, both Priestley's politics and religion became very unpopular in England. On the second anniversary of the storming of the Bastille, 14 July 1791, a Birmingham mob burned the Unitarian Meeting House and then the houses of Priestley and other dissenters. As the most reviled man in England, he fled to America in 1794. Jan Ingen-Housz (1730–1799) was the son of a prosperous Dutch merchant and pharmacist, and both father and son became friends with Sir John Pringle when he was stationed near their Brenda home with the British Army. Because the family was Catholic in a Protestant country, Ingen-Housz went to the Catholic University of Louvain in Belgium for his M.D. degree, summa cum laude in 1753. He then spent a year at the University of Leiden, probably upon Pringle's advice. Next, he practiced medicine in Brenda until his father died in 1764, and then moved to London. He became an expert at smallpox inoculation, and in 1768 George III recommended him to Empress Maria Theresa to inoculate her family. She appointed him court physician for life, and he lived in Vienna until 1788, though he frequently visited Paris and London. In 1788 he settled in Paris until the storming of the Bastille on 14 July 1789 alarmed him. He departed for Belgium and The Netherlands, where, as an Austrian courtier, he was viewed with suspicion, and so he returned to live in London (van der Pas 1973, Smit 1980, Ingen Housz 2005). Ingen-Housz became interested in plant growth after reading Priestley's first article and Pringle's Royal Society speech when Priestley won the Copley Medal. However, his Austrian responsibilities prevented him from investigating the subject until the summer of 1779, which he spent in England and conducted the extensive experiments reported in Experiments upon Vegetables, Discovering Their Great Power of Purifying the Common Air in the Sun-shine, and of Injuring it in the and at partly reprinted in Leicester and Klickstein He the of Priestley's results plants air (Partington Nash and with extensive from his and both and Morton is Morton's with chemical of oxygen only in in of plants. of oxygen in the is produced by all of plants in of oxygen in of carbon at of oxygen on the of on not heat. is produced on the surface of leaves. In Ingen-Housz translated his book into and others translated it into Dutch and Priestley some of and in Ingen-Housz discussed with his how to and Schofield only was he his discoveries Priestley was still in the there were other with he conducted One of his was the Geneva who was a of Bonnet a history of his early research on plants, that he began in He was by of the French of Experiments Ingen-Housz had discovered that in water a leaf no “dephlogisticated air” water no leaf no but he did not draw the important conclusion from this discovery that They both knew that pump water was in “fixed air” and that plants produce dephlogisticated air in pump in his nature that fixed air be for plants to dephlogisticated air. This was his most important discovery (Nash Morton Ingen-Housz considered to be of his work from the of the and of the experiments the used and the However, the acknowledged of one experiments by another is not In he was to conclusion that plants the atmosphere at night, but in 1788 he that his further experiments did it, though he it less important than Ingen-Housz thought (Nash some from who him that his in that air” mixed with air” “fixed air” was (Nash Partington the in which was being in by who in the in contrast to the Partington Ihde Guerlac 1973, 1996, However, was to experiments by Cavendish, and Priestley to if he could That research but was not limited the of plant growth. out to the phlogiston The that his was that in the of the weighed less than the and in the of the weighed more than the yet both were explained in the same of phlogiston. In the of phlogiston had a in the of a made little progress in his revolution until Priestley came to Paris two after he had discovered “dephlogisticated air” in 1774 and him about it. then several before his experiment in April that air is not a and that air is of the or in the revolution by him and three partly reprinted in Leicester and Klickstein Partington After work on animal respiration, was inspired by Priestley and experiments to plant growth and he his chemical understanding in doing so chemical revolution with the French Revolution (Conant his textbook, a after the storming of the Priestley was to America of the French was his of it, a of the in the of plants they grow in in or in it is that the plants not the from these and water is to does not air, water it that one may that if some of plants relieve the water of its by with the the oxygen from the plant by the of Ingen-Housz had to the of both and his 1789, in the second of his he had some of chemistry and an of the chemical of However, he did not yet that carbon is in leaves and oxygen into the air. He finally in an on the of Plants and the of up to in was like Priestley doing so in it was not the was to with a new was the son of a who was primarily a but broad interests botany and Although the son a education at he science from his father and Hales was the founder of plant it the of to the status of a science, with its of theory and specific (Morton He never the of phlogiston he the new chemistry from the His first was an extensive published in the article the understanding of and carbon and the for his which is the of

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