Hoagland, Dennis Robert

(b. Golden, Colorado, 2 April 1884; d. Oakland, California, 5 September 1949)

plant physiology

The son of Charles Breckinridge and Lillian May Burch, Hoagland spent his first eight years in Golden. During his later childhood he lived in Denver, where he attended East Denver High School. Majoring in chemistry, he graduated in 1907 from Stanford University. He accepted a position in 1908 as an instructor and assistant in the laboratory of animal nutrition at the University of California at Berkeley. In 1910 he was appointed assistant chemist in the Food and Drug Administration of the U.S. Department of Agriculture, working both in Berkeley and Philadelphia while engaged in a project evaluating the toxicity of aluminum, copper, and sulfur compounds as contaminants of canned foods and dried fruits.

In 1912 Hoagland entered the graduate school of the University of Wisconsin where he worked with E. V. McCollum in the Department of Agricultural Chemistry. In 1913 he received his master’s degree. The next year he joined the Berkeley faculty as an assistant professor in agricultural chemistry and became associate professor in 1922. He became professor in 1927, retiring in 1949. In 1922 a division of plant nutrition within the University of California Collge of Agriculture was established with Hoagland as its head. He also served as president of various organizations, including the American Society of Plant Physiologists, the Pacific Division of the American Association for the Advancement of Science, the Western Society of Naturalists, and the Western Society of Soil Science, and as consulting editor of the journal Soil Science and of the Annual Review of Biochemistry. He was elected a member of the National Academy of Sciences in 1934. In 1920 Hoagland married Jessie A. Smiley of San Francisco. She died in 1933. They had three sons, Robert charles, Albert Smiley, and Charles Rightmire.

Hoagland is best known for his research in process of salt absorption by plants, in soil and plant interrelations, and in the utilization of various elements in soil solutions. Upon his appointment to Berkeley in 1913 as an agricultural chemist, he undertook a systematic investigation of the giant kelps that grow off the California coast. There was at the time a great need for potash fertilizers in this country as a result of the wartime cessation of imports from Germany, and Hoagland believed that the kelps might be a potential source of potassium. Although his findings were not very encouraging, the investigation raised a number of questions that were to stimulate his later research. Specifically, Hoagland was impressed by the ability of kelp to accumulate and retain large amounts potassium, bromide, and iodide.

He found that the principal ions within the kelp cell often contained at far higher concentrations than in the solutions in which they grow. It was therefore important to know how the solutes penetrated, not merely to equality of concentration but to accumulations of far higher concentrations.

In the work of Hoagland and his co-workers, the internodal cells of the freshwater alga Nitella proved particularly useful in studying active secretion of solutes. These long, multinucleate internodal cells yielded drops of liquid from their vacuoles which, when analyzed, showed that virtually all the ionic constituents present in pond water had been accumulated in the cell. This was particularly true of potassium and chloride. Having found that the strength of the solution inside the cell varied according to the season of the year and to light conditions, Hoagland proceeded to study an ion which had not previously been present in the solution and which, once absorbed by the Nitella, could be determined chemically with great accuracy. Using the bromide ion, Hoagland, Hibbard, and Davis (1926) showed that the accumulation of bromide ion from the external solution was a function of the intensity of light, that it occurred little if at all in darkness and was affected by the duration and intensity of light during the daily period of illumination. Hoagland then realized that the Nitella cell was using its light energy to bring about the absorption of the salt through its metabolic processes, and in doing so expended its energy.

Work on thin disks cut from plant storage organs such as potato and artichoke tubers by Steward, first in England, and then later in Hoagland’s laboratory at Berkeley, drew attention to the role of oxygen pressure in this active accumulation process; and thus to the importance of aerobic metabolism in the process of ion intake (cf. Hoagland and Broyer, 1936; Steward and Broyer, 1934; Steward et al., 1936). Absorption of ions by excised roots of barley was soon shown to present similar features. Hoagland’s barley roots were grown in such a way that they contained little salt and had, therefore, a great ability to accumulate potassium bromide. This accumulation occurred when the solutions were appropriately aerated with an air stream free of carbon dioxide. An interesting discovery was that the barley roots accumulated sugar, which was supplied by the leaves during their growth; that when the roots had free access to salt, they rapidly replaced the previously accumulated sugar with the salt that would have been absorbed during growth, had it been freely available. Thus the process of accumulation of solute and salt was shown to be a normal concomitant of the active growth of cells. Metabolites elaborated in one part of the cell, or solutes from the external environment, are secreted into a vacuole as the cell grows. However, once large vacuoles have been produced which have built up within themselves a concentration of solute, there may be interchange with the external medium, entailing a more limited requirement for metabolism and active growth. These conclusions, directly derived from Hoagland’s laboratory work, induced plant physiologists to appreciate that the growing cell is a working molecular machine and that Fick’s diffusion law and passive permeability sensu stricto play a secondary role in active salt accumulation. Interestingly, biologists have yet to identify precisely how such energy is donated and how this secretory machine works.

Hoagland’s Lectures on the Inorganic Nutrition of Plants (Prather lectures at Harvard University), published in 1948, amply summarize his views and philosophy of plant nutrition. Our current understanding of the field owes much to his significant contributions. Following the discovery that plants could be grown in water containing salts, the composition of solutions was modified in various ways. The typical inorganic culture solution widely used today is associated with Hoagland’s name and was based on the proportions of macronutrients absorbed by tomatoes. This solution proved to be efficient for sand and water cultures for a wide range of plants, especially at high light intensities. Hoagland was also involved in the investigation of “little leaf,” a disease of deciduous fruit trees. He traced this and other dieback symptoms in the sandy soils of California to nutritional deficiencies caused by the absence of zinc; other required trace elements were also discovered at his laboratory.

BIBLIOGRAPHY

I. Original Works. Hoagland’s works include “General Nature of the Process of Salt Accumulation by Roots With Description of Experimental Methods,” in Plant Physiology, 11 (1936), 471–507, written with T. C. Broyer; and “The Influence of Light, Temperature, and Other Conditions on the Ability of Nitella Cells to Concentrate Halogens in the Cell Sap,” in Journal of General Physiology, 10 (1926), 121–146, written with P. L. Hibbard and A. R. Davis.

II. Secondary Literature. See two articles by D. I. Arnon: “Dennis Robert Hoagland 1884–1949,” in Plant Physiology, 25 (1950), iv–xvi, abridged in Science, 112 (1950), 739–742; and “Dennis Robert Hoagland 1884–1949,” in Plant and soil, 2 (1950), 129–144, abridged in Soil Science, 69 (1950), 1–5. See also W. P. Kelley, “Dennis Robert Hoagland 1884–1949,” in Biographical Memoirs. National Academy of Sciences, 29 (1956), 123–143, including a complete bibliography; National Cyclopedia of American Biography, XLVII (New York, 1965), 598–599; F. C. Steward and W. F. Berry, “The Absorption and Accumulation of Solutes by Living Plant Cells. VII. The Time Factor in the Respiration and Salt Absorption of Jerusalem Artichoke Tissue (Helianthus tuberosus) With Observations on Ionic Interchange,” in Journal of Experimental Botany, 11 (1934), 103–119; and F. C. Steward, W. E. Berry, and T. C. Broyer, “The Absorption and Accumulation of Solutes by Living Plant Cells. VIII. The Effect of Oxygen Upon Respiration and Salt Accumulation,” in Annals of Botany, 50 (1936), 345–366.

A. D. Krikorian