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Dennis Robert Hoagland

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Dennis Robert Hoagland
BornApril 2, 1884
Golden, Colorado, United States
DiedSeptember 5, 1949 (1949-09-06) (aged 65)
Oakland, California, United States
Alma materStanford University (Bachelor)
University of Wisconsin-Madison (Master)
Known forHoagland solution, Active transport, Nitella, Plant-soil interrelationship, Plant nutrition, Hoagland and Knop medium
AwardsNewcomb Cleveland Prize
Scientific career
FieldsPlant physiology
Soil chemistry
InstitutionsUniversity of California, Berkeley
Doctoral studentsDaniel I. Arnon
InfluencesWilhelm Knop
Julius von Sachs

Dennis Robert Hoagland (April 2, 1884 – September 5, 1949) was an American chemist and plant scientist working in the fields of plant nutrition, agricultural chemistry, and physiology. He was Professor of Plant Nutrition at the University of California at Berkeley from 1927 until his death in 1949. Hoagland is commonly known for discovering the active transport of nutrients in plants, using innovative model systems under controlled experimental conditions, such as solution culture. He developed an artificial nutrient solution, universally known as Hoagland solution.[1]

Discover more about Dennis Robert Hoagland related topics



A chemist is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms. Chemists carefully measure substance proportions, chemical reaction rates, and other chemical properties. In Commonwealth English, pharmacists are often called chemists.



Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude the fungi and some algae, as well as the prokaryotes. By one definition, plants form the clade Viridiplantae which is sister of the Glaucophyta, and consists of the green algae and Embryophyta. The latter includes the flowering plants, conifers and other gymnosperms, ferns and their allies, hornworts, liverworts, and mosses.

Plant nutrition

Plant nutrition

Plant nutrition is the study of the chemical elements and compounds necessary for plant growth and reproduction, plant metabolism and their external supply. In its absence the plant is unable to complete a normal life cycle, or that the element is part of some essential plant constituent or metabolite. This is in accordance with Justus von Liebig’s law of the minimum. The total essential plant nutrients include seventeen different elements: carbon, oxygen and hydrogen which are absorbed from the air, whereas other nutrients including nitrogen are typically obtained from the soil.

Agricultural chemistry

Agricultural chemistry

Agricultural chemistry is the study of chemistry, especially organic chemistry and biochemistry, as they relate to agriculture—agricultural production, the processing of raw products into foods and beverages, and environmental monitoring and remediation. These studies emphasize the relationships between plants, animals and bacteria and their environment. As a branch of agricultural science, agricultural chemistry studies the chemical compositions and reactions involved in the production, protection, and use of crops and livestock. Its basic science aspects embrace, in addition to test-tube chemistry, all the life processes through which humans obtain food and fiber for themselves and feed for their animals. Its applied science and technology aspects are directed toward control of those processes to increase yields, improve quality, and reduce costs. One important branch of it, chemurgy, is concerned chiefly with utilization of agricultural products as chemical raw materials.



Physiology is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical and physical functions in a living system. According to the classes of organisms, the field can be divided into medical physiology, animal physiology, plant physiology, cell physiology, and comparative physiology.



Professor is an academic rank at universities and other post-secondary education and research institutions in most countries. Literally, professor derives from Latin as a "person who professes". Professors are usually experts in their field and teachers of the highest rank.

Active transport

Active transport

In cellular biology, active transport is the movement of molecules or ions across a cell membrane from a region of lower concentration because a region of higher concentration—against the concentration gradient. passive transport requires cellular energy to achieve this movement. There are two types of active transport: primary active transport that uses adenosine triphosphate (ATP), and secondary active transport that uses an electrochemical gradient.



A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excreted by cells to create non-cellular structures, such as hair, scales, feathers, or exoskeletons. Some nutrients can be metabolically converted to smaller molecules in the process of releasing energy, such as for carbohydrates, lipids, proteins, and fermentation products, leading to end-products of water and carbon dioxide. All organisms require water. Essential nutrients for animals are the energy sources, some of the amino acids that are combined to create proteins, a subset of fatty acids, vitamins and certain minerals. Plants require more diverse minerals absorbed through roots, plus carbon dioxide and oxygen absorbed through leaves. Fungi live on dead or living organic matter and meet nutrient needs from their host.

Model organism

Model organism

A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Model organisms are widely used to research human disease when human experimentation would be unfeasible or unethical. This strategy is made possible by the common descent of all living organisms, and the conservation of metabolic and developmental pathways and genetic material over the course of evolution.



Hydroponics is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops or medicinal plants, without soil, by using water-based mineral nutrient solutions in aqueous solvents. Terrestrial or aquatic plants may grow with their roots exposed to the nutritious liquid or in addition, the roots may be mechanically supported by an inert medium such as perlite, gravel, or other substrates.



Artificiality is the state of being the product of intentional human manufacture, rather than occurring naturally through processes not involving or requiring human activity.

Hoagland solution

Hoagland solution

The Hoagland solution is a hydroponic nutrient solution that was newly developed by Hoagland and Snyder in 1933, modified by Hoagland and Arnon in 1938, and revised by Arnon in 1950. It is one of the most popular artificial solution compositions for growing plants, in the scientific world at least, with more than 17,000 citations listed by Google Scholar. The Hoagland solution provides all essential elements for plant nutrition and is appropriate for supporting normal growth of a large variety of plant species.


Private life

Dennis Hoagland was the son of Charles Breckinridge Hoagland (1859 – 1934) and Lillian May Hoagland (1863 – 1951). He spent his first eight years in Golden and during his later childhood he lived in Denver. He attended the Denver public schools and in 1903 entered Stanford University. In 1920, Dennis R. Hoagland married Jessie A. Smiley. She died suddenly of pneumonia in 1933. He was left with the responsibility of bringing up three young boys named Robert Charles, Albert Smiley, and Charles Rightmire.[2]


Hoagland graduated from Stanford University (1907) with a major in chemistry. In 1908 he became an instructor and assistant in the Laboratory of Animal Nutrition at the University of California at Berkeley, an institution with which he would be associated for the remainder of his life. There he worked in the fields of animal nutrition and biochemistry. In 1910 he was appointed assistant chemist in the Food and Drug Administration of the U.S. Department of Agriculture until 1912 (Schmidt and Hoagland, 1912), when he entered the graduate school in the department of agricultural chemistry with Elmer McCollum at the University of Wisconsin, receiving his master's degree in 1913 (McCollumn and Hoagland, 1913). In the fall of that year he became assistant professor of agricultural chemistry and in 1922 associate professor of plant nutrition at Berkeley.[3]


Brief overview

During World War I, Hoagland tried to substitute the lack of imports of potassium-based fertilizers from the German Empire to the United States with plant extracts from brown algae, inspired by the ability of giant kelp to absorb elements from seawater selectively and to accumulate potassium and iodide many times in excess of the concentrations found in seawater (Hoagland, 1915). Based on these findings he investigated the ability of plants to absorb salts against a concentration gradient and discovered the dependence of nutrient absorption and translocation on metabolic energy using innovative model systems under controlled experimental conditions (Hoagland, Hibbard, and Davis, 1926). During his systematic research, mainly by solution culture technique, and inspired by a principle of Julius von Sachs, he developed the basic formula for the Hoagland solution, whose composition was originally patterned after the displaced soil solution obtained from certain soils of high productivity (Hoagland, 1919)1. His research also led to new discoveries on the need and function of trace elements required by living cells, thus establishing the essentiality of molybdenum for the growth of tomato plants (Arnon and Hoagland, 1940; Hoagland, 1945). Hoagland was able to show that various plant diseases are caused by a lack of trace elements such as zinc (Hoagland, Chandler, and Hibbard, 1931, ff.), and that boron, manganese, zinc, and copper are indispensable for normal plant growth (Hoagland, 1937). He took special interest in soil-plant interrelationships addressing, for example, the physiological balance of soil solutions and the pH dependence of plant growth, in order to gain a better understanding on the availability and absorption of nutrients in soils and solutions (Hoagland, 1916, 1917, 1920, 1922; Hoagland and Arnon, 1941). Hoagland and his associates, including his research assistant William Z. Hassid,[4] thus contributed to the understanding of fundamental cellular physiological processes in green plants that are driven by sunlight as the ultimate form of energy (Hoagland and Davis, 1929; Hoagland and Steward, 1939, 1940; Hoagland, 1944, 1946).[5]

Hoagland's and Knop's solutions

Dennis Hoagland was the first to develop a new type of solution based on the composition of the soil solution (Hoagland, 1919)1. He also developed the first successful concept for distinguishing between concentration and total amount of nutrients in a solution (Johnston and Hoagland, 1929). The term Hoagland solution was first mentioned by Olof Arrhenius in 1922 with reference to the Hoagland publication of 1919 where he defined an optimum nutrient solution as "the minimum concentration which gave maximum yield and beyond there was no further improvement".[6][7] The respective solution published by Hoagland in 1920 was applied to investigate plant growth parameters of barley in comparison with Shive's solution.[8] The growth of Alfalfa in a modified Hoagland solution was investigated at various pH values in the 1920s.[9] Around the 1930s Hoagland and his associates[4] investigated diseases of certain plants, and thereby, observed symptoms related to existing soil conditions such as salinity. In this context, Hoagland undertook water culture experiments with the hope of delivering similar symptoms under controlled laboratory conditions. For these experiments the Hoagland solution (0) including macronutrients, iron, and the supplementary solutions A and B, was newly developed to investigate certain diseases of the strawberry in California (Hoagland and Snyder, 1933).

Hoagland's research was supported by the plant pathologists H. E. Thomas and W. C. Snyder, and influenced by another pioneer of plant nutrition and hydroculture, William Frederick Gericke.[10] Gericke's groundbreaking results in applying the principles of water culture to commercial agriculture inspired him to expand his research on the subject finally resulting in the Hoagland solutions (1) and (2) (Hoagland and Arnon, 1938, 1950).[11] The composition and concentration of macronutrients of the Hoagland solutions (0) and (1) can be traced back to Wilhelm Knop's four-salt mixture[12] and the molar ratio to experimental results of Hoagland and his associates (cf. Tables (1) and (2)). Knop's solution, in contrast to Hoagland's solution, was not supplemented with trace elements (micronutrients), with the exception of iron, because the chemicals were not particularly pure in Wilhelm Knop's day. Micronutrients were, without knowing it, already present as impurities in the macronutrient salts. More highly purified chemicals and more sensitive methods for analysing trace concentrations were developed from 1930 and onwards.[13]

Knop's four-salt mixture

Table (1). Knop's four-salt mixture (1865)[14]

Macronutrient salts Quantities in solution
KNO3 0.25
Ca(NO3)2 1.00
MgSO4•7H2O 0.25
KH2PO4 0.25

Table (2). Composition and full concentration of macronutrients in Hoagland's solution (0, 1, 2) and in Knop's solution[14][15][16]

Macronutrients Hoagland's solution (0, 1) Hoagland's solution (2) Knop's solution
Quantities in solution
µmol/L µmol/L µmol/L
K+ 6,000 6,000 4,310
Ca2+ 5,000 4,000 6,094
Mg2+ 2,000 2,000 1,014
15,000 14,000 14,661
- 1,000 -
2,000 2,000 1,014
1,000 1,000 1,837

Hoagland's students included Daniel Israel Arnon who modified the composition of macronutrients of the Hoagland solution (2) (cf. Table 2) and the concentration of micronutrients (B, Mn, Zn, Cu, Mo, and Cl) of the Hoagland solutions (1) and (2) (cf. Table (3)) as a result of joint efforts,[17] and Folke Karl Skoog.[4] In contrast to the Murashige and Skoog medium, neither vitamins nor other organic compounds are provided as additives for the Hoagland solution, but only essential minerals as ingredients. Murashige and Skoog concluded that the promotion of growth of tobacco callus cultured on White's modified medium is due mainly to inorganic rather than organic constituents in aqueous tobacco leaf extracts added.[18]


Table (3). Composition and full concentration of essential micronutrients in Hoagland's solution (0, 1, 2)[15][16]

Micronutrients Hoagland's solution (0) Hoagland's solution (1, 2)
Quantities in solution
µmol/L µmol/L
B(OH)4 9.88 46.25
Mn2+ 1.97 9.15
Zn2+ 0.34 0.77
Cu2+ 0.22 0.32
- 0.50* or 0.11**
0.18 -
Cl 3.93 18.29

As an additional micronutrient, 9 µM ferric tartrate (C12H12Fe2O18) is added to the Hoagland solution formulations (0, 1, 2), corresponding to a concentration of 18 µmol/L Fe3+. Solution (2) contains ammonium and nitrate salts and may sometimes be preferred to solution (0, 1) (cf. Table 2) because the ammonium ion delays the development of undesirable alkalinity (Hoagland and Arnon, 1938, 1950). However, it is toxic to most crop species and is rarely applied as a sole nitrogen source.[19]

Disputed hypotheses

Hoagland concluded that solutions of radically different concentrations and salt proportions did not affect the yield of a crop to any important extent.[8] More recent studies, however, revealed that growth differences persisted among the commonly used nutrient solutions with already small differences in concentration.[20] As an example, Hoagland's solution (2) led to increased growth of fig trees in high-tunnel and open-field conditions, respectively.[21] One important central aspect of Hoagland's hypothesis that water culture was rarely superior to soil culture ("Yields are not strikingly different under comparable conditions") is questionable (Hoagland and Arnon, 1938, 1950). For example, water culture led to highest biomass and protein production of hydroponically grown tobacco plants compared to other growth substrates, cultivated in the same environmental conditions and supplied with equal amounts of nutrients.[22]

In contrast to Gericke, Hoagland regarded solution culture primarily as a method for discovering scientific laws, while Gericke emphasized that hydroponics wasn't yet a precise science. The authors' differing views are illustrated by the following quotations: "Its commercial application is justifiable under very limited conditions and only under expert supervision" (Hoagland and Arnon, 1938, 1950, The Water Culture Method for Growing Plants Without Soil); "Indeed, it is obvious that since hydroponics requires a larger expense per unit of area than does agriculture, either yields must be larger, or there must be other compensations, if the method is to succeed commercially. And experience has already shown that it can succeed" (Gericke, 1940, Complete Guide to Soilless Gardening). Not surprisingly, the history of hydroponics has proved Gericke right in his claims about the commercial use of this technique.[23]

Awards and honors

Hoagland became a Fellow of the American Association for the Advancement of Science (AAAS) in 1916 and member of the National Academy of Sciences in 1934.[24] In recognition of his many discoveries, the American Society of Plant Physiologists elected Dennis Hoagland as president in 1932[25] and awarded him the first Stephen Hales Prize in 1929.[26] In 1940, together with Daniel I. Arnon, he received the AAAS Newcomb Cleveland Prize for the work "Availability of Nutrients with Special Reference to Physiological Aspects".[27] In 1944 he published his Lectures on the Inorganic Nutrition of Plants subtitled "Prather Lectures at Harvard University" which he was invited in 1942 to give at Harvard University.[28] In 1945 he was elected member of the American Academy of Arts and Sciences.[29]

The Dennis R. Hoagland Award, first presented by the American Society of Plant Biologists in 1985,[30] and Hoagland Hall, which is home to the Atmospheric Science program as well as the Environmental Health and Safety office at the UC Davis, are named in his honor.[31]


Standard nutrient solutions

Nowadays the most common solutions for plant nutrition and plant tissue cultivation are the formulations from Hoagland and Arnon (1938, 1950),[32] and Murashige and Skoog (1962).[33] The basic formulas of Hoagland and Arnon are being replicated by modern manufacturers to produce liquid concentrated fertilizers for plant breeders, farmers, and average consumers. Even the names of Hoagland, Knop, Murashige and Skoog are used as a brand for innovative products, e.g., Hoagland's No. 2 Basal Salt Mixture or Murashige and Skoog Basal Salt Mixture, which are commonly used as standard chemicals in plant science. The Hoagland and Knop medium was specially formulated for plant cell, tissue and organ cultures on agar.

Hoagland and many other plant nutritionists used over 150 different nutrient solution recipes during their careers (cf. Table (4).[7] In fact, several nutrient recipes refer to a standard name although they have little to do with the original formula. For example, as described by Hewitt, several recipes have been published under the name of "Hoagland", and to this day confusion may arise from a loss of memory about the original composition.[34]

Table (4). Composition of selected standard nutrient solutions modified according to Hewitt (Table 30A). Full concentration of the (essential) elements as ppm.[7]

Reference Ca Mg Na K B Mn Cu Zn Mo Fe Cl N P S Comment
Sachs (1860) 266 48 95 386 145 139 78 177 First published standard formula
Knop (1865) 244 24 168 206 57 32 Knop's four-salt mixture
Shive (1915) 208 484 562 148 448 640 Shive's best solution
Hoagland (1919)1 200 99 12 284 18 158 44 123 Based on the soil solution
Hoagland (1920) 172 52 190 158 38 67 Hoagland's optimum solution
Hoagland & Snyder (1933) 200 48.6 235 0.11 0.11 0.014 0.023 0.018 1.0 0.14 210 31 64 Hoagland's solution (0)
Hoagland & Arnon (1938)* 200 48.6 235 0.50 0.50 0.02 0.05 0.048 1.0 0.65 210 31 64 Hoagland's solution (1)
Hoagland & Arnon (1950)** 160 48.6 235 0.50 0.50 0.02 0.05 0.011 1.0 0.65 210 31 64 Hoagland's solution (2)
Jacobson (1951) 10.5 5.0 2.9 Jacobson's solution
Hewitt (1952, 1966) 160 36 31 156 0.54 0.55 0.064 0.065 0.048 2.8 168 41 48 Long Ashton nutrient solution

Hybrid nutrient solutions

Hybrid nutrient solutions consisting of macronutrients of a modified Hoagland solution (1), micronutrients of a modified Long Ashton solution, and iron of a modified Jacobson solution, combine the physiological properties of different standard solutions to create a balanced nutrient solution that enables optimum plant growth diluted to 13 of the full solution (cf. Table (5)).[15][35]

Table (5). Composition of a hybrid nutrient solution modified according to Hoagland and Arnon (1938), Jacobson (1951), and Hewitt (1966). Full elemental concentration in ppm.[15][35]

Reference Ca Mg Na K B Mn Cu Zn Mo Fe Cl N P S Comment
Nagel et al. (2020) 200 48.6 0.023 246 0.54 0.55 0.064 0.065 0.048 5.0 0.71 210 31 67 Hybrid nutrient solution

Hoagland's legacy

Dennis Hoagland was considered a leading scientist in his field of research and his lingering research merit was to initiate and to establish the solution named after him, thereby, creating the basis for a balanced plant nutrition that is still valid today.[16] The Hoagland solution is not only used on earth, but has also proven itself in plant production experiments on the International Space Station.[36] The findings of Hoagland and his associates are relevant to the sustainable use of natural resources such as soil, water and air, water and nutrient use efficiency in crop production and the production of healthy plant foods.[37] Hoagland's fundamental scientific contributions and widely cited publications are of historical relevance to research in modern plant nutrition, plant physiology, and soil chemistry, which is reflected in the following bibliography.[38]

Discover more about Biography related topics

Golden, Colorado

Golden, Colorado

Golden is a home rule city that is the county seat of Jefferson County, Colorado, United States. The city population was 20,399 at the 2020 United States Census. Golden lies along Clear Creek at the base of the Front Range of the Rocky Mountains. Founded during the Pike's Peak Gold Rush on June 16, 1859, the mining camp was originally named Golden City in honor of Thomas L. Golden. Golden City served as the capital of the provisional Territory of Jefferson from 1860 to 1861, and capital of the official Territory of Colorado from 1862 to 1867. In 1867, the territorial capital was moved about 12 miles (19 km) east to Denver City. Golden is now a part of the Denver–Aurora–Lakewood, CO Metropolitan Statistical Area and the Front Range Urban Corridor.



Denver is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 a 19.22% increase since the 2010 United States census. It is the 19th-most populous city in the United States and the fifth most populous state capital. It is the principal city of the Denver–Aurora–Lakewood, CO Metropolitan Statistical Area and the first city of the Front Range Urban Corridor.



Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances. Chemistry also addresses the nature of chemical bonds in chemical compounds.

Animal nutrition

Animal nutrition

Animal nutrition focuses on the dietary nutrients needs of animals, primarily those in agriculture and food production, but also in zoos, aquariums, and wildlife management.



Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and metabolism. Over the last decades of the 20th century, biochemistry has become successful at explaining living processes through these three disciplines. Almost all areas of the life sciences are being uncovered and developed through biochemical methodology and research. Biochemistry focuses on understanding the chemical basis which allows biological molecules to give rise to the processes that occur within living cells and between cells, in turn relating greatly to the understanding of tissues and organs, as well as organism structure and function. Biochemistry is closely related to molecular biology, which is the study of the molecular mechanisms of biological phenomena.

Food and Drug Administration

Food and Drug Administration

The United States Food and Drug Administration is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food safety, tobacco products, dietary supplements, prescription and over-the-counter pharmaceutical drugs (medications), vaccines, biopharmaceuticals, blood transfusions, medical devices, electromagnetic radiation emitting devices (ERED), cosmetics, animal foods & feed and veterinary products.

Elmer McCollum

Elmer McCollum

Elmer Verner McCollum was an American biochemist known for his work on the influence of diet on health. McCollum is also remembered for starting the first rat colony in the United States to be used for nutrition research. His reputation has suffered from posthumous controversy. Time magazine called him Dr. Vitamin. His rule was, "Eat what you want after you have eaten what you should."



A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Many sources of fertilizer exist, both natural and industrially produced. For most modern agricultural practices, fertilization focuses on three main macro nutrients: nitrogen (N), phosphorus (P), and potassium (K) with occasional addition of supplements like rock dust for micronutrients. Farmers apply these fertilizers in a variety of ways: through dry or pelletized or liquid application processes, using large agricultural equipment or hand-tool methods.

German Empire

German Empire

The German Empire, also referred to as Imperial Germany, the Kaiserreich, the Second Reich, as well as simply Germany, was the period of the German Reich from the unification of Germany in 1871 until the November Revolution in 1918, when the German Reich changed its form of government from a monarchy to a republic.

Brown algae

Brown algae

Brown algae, comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and polar regions. They are dominant on rocky shores throughout cooler areas of the world. Most brown algae live in marine environments, where they play an important role both as food and as a potential habitat. For instance, Macrocystis, a kelp of the order Laminariales, may reach 60 m (200 ft) in length and forms prominent underwater kelp forests. Kelp forests like these contain a high level of biodiversity. Another example is Sargassum, which creates unique floating mats of seaweed in the tropical waters of the Sargasso Sea that serve as the habitats for many species. Many brown algae, such as members of the order Fucales, commonly grow along rocky seashores. Some members of the class, such as kelps, are used by humans as food.

Macrocystis pyrifera

Macrocystis pyrifera

Macrocystis pyrifera, commonly known as giant kelp or bladder kelp, is a species of kelp, and one of four species in the genus Macrocystis. Despite its appearance, it is not a plant; it is a heterokont. Giant kelp is common along the coast of the northeastern Pacific Ocean, from Baja California north to southeast Alaska, and is also found in the southern oceans near South America, South Africa, Australia, and New Zealand. Individual algae may grow to more than 45 metres long at a rate of as much as 60 cm (2 ft) per day. Giant kelp grows in dense stands known as kelp forests, which are home to many marine animals that depend on the algae for food or shelter. The primary commercial product obtained from giant kelp is alginate, but humans also harvest this species on a limited basis for use directly as food, as it is rich in iodine, potassium, and other minerals. It can be used in cooking in many of the ways other sea vegetables are used, and particularly serves to add flavor to bean dishes.

Chemical element

Chemical element

A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler substances by any chemical reaction. The number of protons in the nucleus is the defining property of an element, and is referred to as its atomic number – all atoms with the same atomic number are atoms of the same element. Almost all of the baryonic matter of the universe is composed of chemical elements. When different elements undergo chemical reactions, atoms are rearranged into new compounds held together by chemical bonds. Only a minority of elements, such as silver and gold, are found uncombined as relatively pure native element minerals. Nearly all other naturally occurring elements occur in the Earth as compounds or mixtures. Air is primarily a mixture of the elements nitrogen, oxygen, and argon, though it does contain compounds including carbon dioxide and water.

Source: "Dennis Robert Hoagland", Wikipedia, Wikimedia Foundation, (2022, December 2nd),

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The Determination of Aluminum in Feces. With C. L. A. Schmidt. J. Biol. Chem., 11(4) :387-391.


Studies of the Endogenous Metabolism of the Pig as Modified by Various Factors. (I.-III.). With E. V. McCollum. J. Biol. Chem., 16(3) :299-315, 317-320, 321-325.


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Physiological Aspects of Soil Solution Investigations. Calif. Agr. Exp. Sta. Hilg., 1(11) :227-257.


Some Phases of the Inorganic Nutrition of Plants in Relation to the Soil Solution: 1. The Growth of Plants in Artificial Culture Media. Sci. Agr., 6(5) :141-151.

Some Phases of the Inorganic Nutrition of Plants in Relation to the Soil Solution: 2. Soil Solutions as Media for Plant Growth. Sci. Agr., 6(6) :177-189.

Effect of Certain Alkali Salts on Growth of Plants. With J. S. Burd and A. R. Davis. (20) Abstract. Nature and Promise of Soil Solution. (21) Abstract of Papers Read Before Pan-Pacific Scientific Congress, Australia.

The Influence of Light, Temperature, and Other Conditions on the Ability of Nitella Cells to Concentrate Halogens in the Cell Sap. With P. L. Hibbard and A. R. Davis. J. Gen. Phys., 10(1) :121-146.

The Investigation of the Soil from the Point of View of the Physiology of the Plant. 4th Int. Conf. Soil Sci. Rome, 1924, 3 :535-544.


The Synthesis of Vitamin E by Plants Grown in Culture Solutions. With H. M. Evans. Am. J. Phys., 80(3) :702-704.

Recent Experiments Concerning the Adequacy of Artificial Culture Solutions and of Soil Solutions for the Growth of Different Types of Plants. With J. C. Martin. Proceedings and Papers of the First Int. Cong. Soil Sci., 3 :1-12.

Resume of Recent Soil Investigations at the University of California. Mo. Bull. Calif. Dept. Agr., 16(11) :562-568.


First International Congress of Soil Science, Fourth Commission, Soil Fertility. (Summary.) Soil Sci., 25(1) :45-50.

The Influence of One Ion on the Accumulation of Another by Plant Cells with Special Reference to Experiments with Nitella. With A. R. Davis and P. L. Hibbard. Plant Phys., 3(4) :473-486.

An Apparatus for the Growth of Plants in Controlled Environment. With A. R. Davis. Plant Phys., 3(3) :277-292.


Minimum Potassium Level Required by Tomato Plants Grown in Water Cultures. With E. S. Johnston. Soil Sci., 27(2) :89-109.

The Intake and Accumulation of Electrolytes by Plant Cells. With A. R. Davis. Protoplasma, 6(4) :610-626.


Fertilizer Problems and Analysis of Soils in California. Calif. Agr. Exp. Sta. Cir., 317 :1-16.

Accumulation of Mineral Elements by Plant Cells. Contrib. Marine Biol., pp.  131–144.

Recent Advances in Plant Physiology. Ecology, 11(4) :785-786.


Little-Leaf or Rosette in Fruit Trees, I. With W. H. Chandler and P. L. Hibbard. Proc. Am. Soc. Hort. Sci., 28 :556-560.

Absorption of Mineral Elements by Plants in Relation to Soil Problems. Plant Phys., 6(3) :373-388.


Little-Leaf or Rosette of Fruit Trees, II: Effect of Zinc and Other Treatments. With W. H. Chandler and P. L. Hibbard. Proc. Am. Soc. Hort. Sci., 29 :255-263.

Mineral Nutrition of Plants. Annu. Rev. Biochem., 1 :618-636.

Some Effects of Deficiencies of Phosphate and Potassium on the Growth and Composition of Fruit Trees under Controlled Conditions. With W. H. Chandler. Proc. Am. Soc. Hort. Sci., 29 :267-271.


Little-Leaf or Rosette of Fruit Trees, III. With W. H. Chandler and P. L. Hibbard. Proc. Am. Soc. Hort. Sci., 30 :70-86.

Mineral Nutrition of Plants. Annu. Rev. Biochem., 2 :471-484.

Nutrition of Strawberry Plant under Controlled Conditions. (a) Effects of Deficiencies of Boron and Certain Other Elements, (b) Susceptibility to Injury from Sodium Salts. With W. C. Snyder. Proc. Am. Soc. Hort. Sci., 30 :288–294.

Absorption of Potassium by Plants in Relation to Replaceable, Non-Replaceable, and Soil Solution Potassium. With J. C. Martin. Soil Sci., 36 :1-33.

Methods for Determining Availability of Potassium with Special Reference to Semi-Arid Soils. Trans. 2nd Commission and Alkali Subcommission of the International Soc. Soil Sci. Kjobenhavn (Danmark). Vol. A, pp.  25–31.


Little-Leaf or Rosette of Fruit Trees, IV. With W. H. Chandler and P. L. Hibbard. Proc. Am. Soc. Hort. Sci., 32 :11-19.

The Potassium Nutrition of Barley with Special Reference to California Soils. Proc. Fifth Pacific Science Congress, pp.  2669–2676.


Little-Leaf or Rosette of Fruit Trees, V: Effect of Zinc on the Growth of Plants of Various Types in Controlled Soil and Water Culture Experiments. With W. H. Chandler and P. L. Hibbard. Proc. Am. Soc. Hort. Sci., 33 :131-141.

Comments on the Article by A Kozlowski on "Little Leaf or Rosette of Fruit Trees in California". With W. H. Chandler. Phytopathology, 25(5) :522-522

Absorption of Potassium by Plants and Fixation by the Soil in Relation to Certain Methods for Estimating Available Nutrients. With J. C. Martin. Trans. Third Inter. Cong. Soil Sci., 1 :99-103.


Little-Leaf or Rosette of Fruit Trees, VI: Further Experiments Bearing on the Cause of the Disease. With W. H. Chandler and P. R. Stout. Proc. Am. Soc. Hort. Sci., 34 :210-212.

The Plant as a Metabolic Unit in the Soil-Plant System. Essays in Geobotany in Honor of Wm. A. Setchell. Univ. Calif. Press, pp. 219–245.

General Nature of the Process of Salt Accumulation by Roots with Description of Experimental Methods. With T. C. Broyer. Plant Phys., 11(3) :471-507.


Some Aspects of the Salt Nutrition of Higher Plants. Bot. Rev., 3 :307-334.


The Water-Culture Method for Growing Plants without Soil. With D. I. Arnon. Calif. Agr. Exp. Sta. Cir., 347, pp.  1-39.*

Fertilizer Problems and Analysis of Soils in California. Calif. Agr. Exp. Sta. Cir., 317 :1-16 (Revision).


A Comparison of Water Culture and Soil as Media for Crop Production. With D. I. Arnon. Science, 89 :512-514.

Upward and Lateral Movement of Salt in Certain Plants as Indicated by Radioactive Isotopes of Potassium, Sodium, and Phosphorus Absorbed by Roots. With P. R. Stout. Am. J. Bot., 26(5) :320-324.

Metabolism and Salt Absorption by Plants. With F. C. Steward. Nature, 143 :1031-1032.


Salt Absorption by Plants. With F. C. Steward. Nature, 145 :116-117.

Hydrogen-Ion Effects and the Accumulation of Salt by Barley Roots as Influenced by Metabolism. With T. C. Broyer. Am. J. Bot., 27 :173-185.

Upward Movement of Salt in the Plant. With T. C. Broyer and P. R. Stout. Nature, 146 :340-340.

Minute Amounts of Chemical Elements in Relation to Plant Growth. Science, 91 :557-560.

Methods of Sap Expression from Plant Tissues with Special Reference to Studies on Salt Accumulation by Excised Barley Roots. With T. C. Broyer. Am. J. Bot., 27(7) :501-511.

Crop Production in Artificial Culture Solutions and in Soils with Special Reference to Factors Influencing Yields and Absorption of Inorganic Nutrients. With D. I. Arnon. Soil Sci., 50(1) :463-485.

Salt Accumulation by Plant Cells with Special Reference to Metabolism and Experiments on Barley Roots. Cold Spring Harbor Symposia on Quantitative Biology, Vol. 8.

Some Modern Advances in the Study of Plant Nutrition. Proc. Am. Soc. Sugar Beet Tech., Part 1 :18-26.


Water Culture Experiments on Molybdenum and Copper Deficiencies of Fruit Trees. Proc. Am. Soc. Hort. Sci., 38 :8-12.

Physiological Aspects of Availability of Nutrients for Plant Growth. With D. I. Arnon. Soil Sci., 51(1) :431-444.

Aspects of Progress in the Study of Plant Nutrition. Trop. Agr., 18 :247.


Accumulation of Salt and Permeability in Plant Cells. With T. C. Broyer. J. Gen. Physiol., 25(6) :865-880.


Metabolic Activities of Roots and Their Bearing on the Relation of Upward Movement of Salts and Water in Plants. With T. C. Broyer. Am. J. Bot., 30(4) :261-273.

Composition of the Tomato Plant as Influenced by Nutrient Supply, in Relation to Fruiting. With D. I. Arnon. Bot. Gaz., 104(4) :576-590.


General Aspects of the Study of Plant Nutrition. Sci. Univ. Calif., pp. 279–294.

The Investigation of Plant Nutrition by Artificial Culture Methods. With D. I. Arnon. Biol. Rev. Cambr. Phil. Soc., 19(2) :55-67.

Lectures on the Inorganic Nutrition of Plants. (Prather Lectures at Harvard University). Published by Chronica Botanica Co. Waltham, Mass.


Molybdenum in Relation to Plant Growth. Soil Sci., 60(2) :119-123.

Potassium Fixation in Soils in Replaceable and Non-Replaceable Forms in Relation to Chemical Reactions in the Soil. With J. C. Martin and R. Overstreet. Soil Sci. Soc. Am. Proc., 10 :94-101.


The Nutrition and Biochemistry of Plants, Currents in Biochemical Research. Interscience Publ. Inc. N. Y., pp.  61–77.

Little-Leaf or Rosette of Fruit Trees, VIII: Zinc and Copper Deficiency in Corral Soils. With W. H. Chandler and J. C. Martin. Proc. Am. Soc. Hort. Sci., 47 :15-19.


Trace Elements in Plants and Animals by Walter Stiles. Rev. Arch. Biochem., 13 :311-312.

Fertilizers, Soil Analysis, and Plant Nutrition. Calif. Agr. Exp. Sta. Cir., 367 :1-24.


Minute Amounts of "Minor" Elements Essential in Addition to "Regular" Fertilizer. Agr. Chem.

Some Problems of Plant Nutrition. With D. I. Arnon. Sci. Mo., 67(3): 201-209.


Fertilizers, Soil Analysis, and Plant Nutrition. Calif. Agr. Exp. Sta. Cir., 367 :1-24 (Revision).

1950 (posthumous)

Absorption and Utilization of Inorganic Substances in Plants. With P. R. Stout. Chap. VIII of Agricultural Chemistry, ed. by Frear, Van Nostrand.

The Water-Culture Method for Growing Plants without Soil. With D. I. Arnon. Calif. Agr. Exp. Sta. Cir., 347, pp.  1-32 (Revision).**

Availability of Potassium to Crops in Relation to Replaceable and Non-Replaceable Potassium and to Effects of Cropping and Organic Matter. With J. C. Martin. Soil Sci. Soc. Am. Proc., 15 :272-278.

Courtesy of The National Academy of Sciences Archives, and without these entries it would not have been possible.

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