Agronomy: A Course in Practical Gardening for High Schools

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Preface

This book has been prepared to meet the needs of high schools in cities and towns where agriculture is taught, and in which the problems that confront the teacher are in some respects different from those that come up in rural communities. The environment of the city child makes it undesirable to emphasize in his case the growing of stock, the production and care of milk, the breeding of animals, and the cultivation of field crops. There is, however, much information of a practical nature regarding the cultivation of plants which he finds necessary for the fullest enjoyment of his surroundings. Though not engaged in growing crops for a livelihood, he is, nevertheless, interested in the cultivation of vegetables and flowers, the making of lawns and their care, the planting of shrubbery, the trimming of trees, and similar matters. In the present volume it has been the aim, therefore, to develop the subject of agriculture from the urban viewpoint, though the matters discussed are fundamental to any system of cultivating plants and are as applicable to rural communities as elsewhere. Furthermore, it is expected that the book will also serve as a practical guide to that part of the general public which, though no longer in school, takes an interest in the cultivation of plants in lawn, garden, and orchard.

Agronomy, as outlined in the following pages, is regarded as a division of agriculture coordinate with animal husbandry. The latter division, though often included in books of this kind, is as distinct from agronomy as zoology is from botany, and has been omitted from this book partly because the subject of agronomy is alone sufficient for one semester's work,

578474 vi AGRONOMY

and partly because city children are not brought much into contact with farm animals. Animal husbandry may well be taught as a separate course, and, if given in the semester following that in which agronomy is given, will afford the pupil a year's continuous work in agriculture. The practical nature of the matter here presented has been proved by several seasons' work with classes in a large citj'^ high school. No directions for work have been given that have not been tried out with such classes.

Agronomy differs from the usual botanical course of the high school in that it is largely the practice of an art rather than the study of a science. It seeks to make the student physically proficient as well as mentally alert. Although usually given after a course in botany, it is by nature an excellent introduction to the more technical study, since it enables the student to bring to bear upon it a considerable first-hand knowledge of plants and plant habits. In the highschool curriculum botany may be considered as existing for the sake of the drill it gives in observation and deduction, as well as for the information it affords, and it is therefore proper that it should be based largely upon experiment. In agronomy, however, experiment has a much smaller place. The fundamentals have so long been a matter of common knowledge that they need not be made the subjects for experiment, though the possibility of proving any phase of the work by this means should not be overlooked.

The course in agronomy here presented is designed to cover a half year of work in the laboratory and school garden and to be given in the spring semester. It is essentially an outdoor course in doing things, with the culture, propagation, and amelioration of plants as the central theme. It presupposes a school garden in which the pupil can carry out the work of cultivating and training plants, and the chief end of the course will be missed if this book is used merely as a

PREFACE vii

convenient source of material for recitations. Few schools are so situated as to make the possession of a school garden absolutely impossible. If the school grounds are not large enough, a vacant lot in the vicinity may be secured by rent or purchase, or the home garden of one of the pupils may be used. Some successfully managed school gardens are ten minutes' walk from the school building. Wherever located the garden ought to be securely fenced against the depredations of the small boy and other irresponsible folk, and a certain degree of permanency should be secured for the plantings, if possible, since at least pai-t of the plants grown will be perennials, . which improve with the years if left undisturbed. Whenever practicable, the school garden should be a part of the school property.

Classes seldom need to be encouraged to take an interest in gardening, but the teacher should see to it that the work is properly planned in advance, that time is allowed for cultivating the crops, and that such experiments are carried on in the experimental plots as will deepen the interest and value of the work to the student. The food, fiber, and drug plants little known in the region may be grown, the many varieties of common vegetables may be tested, and attractive flowers cultivated. Room should also be found for growing all sorts of aberrant plants that may be discovered by the class, such as those possessing double flowers, f asciated stems, color variations, and variations in the cutting of leaves. As a general thing, the crops planted should be such as mature before school closes for the summer or which do not mature until autumn. In the first group are lettuce, spinach, cress, radishes, onions, and turnips; in the second are carrots, parsnips, and salsify. The many forms of radishes now offered by seedsmen are excellent subjects for showing the great variation that may occur in a single plant part. A few experiments may be carried on for a series of years, especially such as viii AGEONOMY

pertain to the training of special shrubs, trees, and viiies, and the propagation or breeding of plants. The greatest success attends a class in which each pupil is allotted space for an individual garden, though two pupils may work in partnership with good results.

Every effort should be made to have the student secure first-hand information. A single visit to an implement store, for instance, will give him more information of real value than hours of recitation about implements which he has never seen or examined. For the same reason frequent field trips to parks, market gardens, nurseries, greenhouses, public gardens, and the like should be made. These trips should, if possible, be taken in the hours allotted to agronomy in the school day and should be counted as part of the regular work. In many cases the period for this study may come last in the day's program, thus allowing pupils to take as much additional time for the work after school as they desire. There is always a tendency on the part of the teacher to assume more knowledge of familiar things than the student possesses, and for this reason it is well to carry out all the exercises suggested, though at first glance some may appear too simple to be worth while.

To the end that the pupils be made conversant with the literature of the subject, they should be encouraged to consult the reference works named at the end of each chapter, as well as more general works such as Bailey's " Cyclopedia of American Horticulture " and '' Cyclopedia of American Agriculture." Each student should also be encouraged to write to the national government for such publications on plants as may interest him. Upon application, the Superintendent of Documents, Government Printing Office, Washington, D. C, will send a list of publications to which a price is attached, and the Editor and Chief of the Division of Publications, Department of Agriculture, will send a monthly list of free

PREFACE ix

publications. In the case of the more expensive publications the pupil's representative in Congress or his senator may secure them free. The publications of his own state agricultural experiment station will also be most useful, and those of other states may often be obtained. All available pamphlets of the kind should, of course, be in the school library. It is often possible to secure enough duplicates of the more important publications to allow one for each member of the class. The pupils should also be supplied with the catalogues of reliable seedsmen and growers of nursery stock. These may usually be had upon request, and the writing of a letter for this purpose may well be made a part of the class work.

At the time the work in agronomy is begun the weather is not likely to be favorable for work in the open, but there are, fortunately, many matters of theory and fact that may be discussed in the classroom before the season for gardening begins, and some of the experiments may also be performed. The book has been arranged, as far as practicable, to follow the progress of the seasons, but in the early weeks of the course the theoretical may overshadow the practical, and matters may be discussed that will not be taken up in a practical way until much later. By looking ahead and selecting those exercises that may be performed as well at one time as at another, the student will be enabled to approach the real work of the course with considerable theoretical knowledge that can be tested later by practice.

One cannot deal intelligently with plants without knowing their names and relationships, and it is recommended that the identification of plants by the use of a good manual of botany be made part of the course. For this work the strictly technical manuals are better than the more popular volumes, since they not only give the names but teach exactness, increase the vocabulary, and familiarize the pupil with the use of scientific keys. The small preliminary instruction needed for the use of

X AGRONOMY

such a manual may be given in the early part of the course, thus preparing the student to name the flowers as fast as they appear.

It is not easy to overestimate the value of all sorts of collections for use in connection with agronomy. The accumulation of striking objects with which to illustrate the course is, however, not a matter of a single year, for the specimens must be secured a few at a time as they are found. Soil maps, typical fungi, seed collections, samples of soils and fertilizers, mineral specimens and pictures of unusual crops, specimen plants, and unfamiliar farming operations all add to the attractiveness and interest of the course. If the school does not possess a museum in which these may be kept, they should be carefully preserved in the laboratory or classroom.

In most cases specific directions for performing an experiment or for carrying on the other work of the course have been omitted from this book, since the conditions in different schools are likely to vary, and the teacher will naturally prefer to work these out to fit his own local conditions. Indeed, in many instances, the planning of the work may be left to the student. No doubt mistakes will be made, but one may learn much from his mistakes. If the pupils have not had an earlier course in botany, or if it is desired to go deeper into the subject of the organization of the plant than is here presented, the author's " Laboratory Botany for the High School " may be found useful.

The sources of the illustrations in this volume are for the most part indicated in connection with the illustrations themselves, but the author takes this opportunity to acknowledge his indebtedness to the Bateman Manufacturing Company, Greenloch, New Jersey ; Wagner s Park Conservatories, Sidney, Ohio ; The Lord and Burnham Company, New York ; and S. L. Allen, Philadelphia, for the loan of photographs and other material. Several illustrations that originally appeared

PREFACE xi

in Duggar's " Fungous Diseases of Plants " and Bergen and Caldwell's " Practical Botany " have been secured through the kindness of the authors of these books. Other drawings in the book are the work of the author's pupils, and the data for the tables of precipitation were supplied by Mr. F. M. Muhlig, United States weather observer at Joliet. The author is especially indebted to his friends, Mr. A. T. Weaver of the American Steel and Wire Company and Mr. Mark Bennitt of the H. L. Hollister Land Company, Chicago, for the use of numerous excellent photographs, and to them, as well as to the others mentioned, he extends his sincere thanks.

For a careful reading of the entire proof and for many helpful suggestions in connection therewith, the author is under deep obligations to his colleague. Professor E. F. Downey of the Flower Technical High School, Chicago; to Professor Grant Smith, Chicago Teachers' College ; and to Professor John H. Schaffner, head of the department of botany, Ohio State University. To his failure to adopt in some instances the sug-^ gestions made, must be attributed such errors as may be detected. By far the larger number of drawings in the book are the work of the author's wife, Ida Martin Clute, and to her he is further indebted for invaluable assistance in preparing the text and in correcting the proofs.

WILLARD X. CLUTE Joliet, Illinois

Contents

PAGE

Chapter I. A Lesson In Chemistry 1

Chemical elements. Atoms and molecules. Chemical formulas. Chemical compounds. Distribution of the elements. Elements found in plants. Potassium. Sodium. Magnesium. Calcium. Aluminum. Iron. Manganese. Oxygen. Hydrogen. Nitrogen. Chlorine. Carbon. Phosphorus. Sulphur. Silicon. Practical exercises.

Chapter II. Origin Of The Soil 11

What the soil is. Depth of the soil. The subsoil. Origin of the soil and subsoil. Weathering. Weathering by decomposition. Weathering by disintegration. Work of glaciers. Modifications of the bed rock. Table of rocks. Changes in mantle rock. Practical exercises.

Chapter III. Types Of Soils 25

Named for their origin. Sedentary soils. Lacustrine soils. JEolian soils. Volcanic soils. Colluvial soils. Glacial soils. Alluvial soils. Soil constituents. Sand and clay contrasted. Loam. Alkali soils. Acid soils. A test for acid soils. Artificial soils. Practical exercises.

Chapter IV. Conditions Affecting Soil Fertility . 38

Structure. The air. Air in the soil. Temperature. Variations in temperature. Other factors that modify temperatures. The Fahrenheit and centigrade scales. Precipitation. Water in the soil. The water table. Drainage. Irrigation. Dry farming. Physiologically dry soils. Practical exercises.

Chapter V. The Organization Of The Plant .... 65

The great plant groups. The regions of the plant. Cellular structure of the plant. Roots. Taproots. Structure of the root. Root hairs. Osmosis. The stem. Structure of the stem. Buds. Leaves. Internal structure of the leaf. Formation of plant food. Transpiration. The flower. Pollination. The fruit. The seed. Life cycle of plants. The rest period of plants. Genera, species, and varieties. Scientific names. Practical exercises.

• • •

xni xiv AGRONOMY

PAGE

CHAITER VI. THE ELEMENTS NEEDED BY PLANT'S ... 95

SiHirce of the elements. Selective absorption. Use of water to the plant. Root pressure. Carbon dioxide. Nitrogen. Calcium and magnesium. Potassium and phosphorus. Sulphur and iron. Chlorine, silicon, and others. Practical exercises.

CHAPTER XIU FERTILIZERS 101

The available mineral in the soil. Toxic substances in the soil. Elements that may be lacking. Sources of the needed elements. Manures. Green manuivs. Nitritication. Bacteria and nitrification. Nitrogen fixation. Mycorrhizas. Soil inoculation. Denitrifying bacteria. Harmful oriraiiisiiis in the soil. Limiting factors in plant growth. Practical exercises.

CHAPTER VIIL THE PLANT IN RELATION TO TEMPERA- TURE, LIGHT, AND MOISTURE 113

Growth temperature. Hardy and tender plants. Cardinal jx^ints. Acclimatization. Frost. Locality and frost. How cold kills plants. Other effects of cold. How plants avoid the effects of cold. Artificial protection from the cold. Treatment of frostbitten plants. Effects of heat. Protection from heat. Need of light. Effects of lack of light. Blanching. Protection from light. Effects of overwatering. Time to water. Effects of lack of water. Water and plant forms. Practical exercises.

CHAPTER IX. GARDEN MAKING 129

Location of the garden. Preparing the soil. The garden plan. How to plant. When to plant. Autumn seed bed. Germination. Seed testing. Double cropping. Transplanting. Inducing plants to fruit. Thinning. Labels. Saving seed. Seed packets. Practical exercises.

CHAPTER X. TILLAGE 149

Need for tillage. Pulverizing the soil. Mulches. Work of earthworms and ants. Rotation of crops. Practical exercises.

CHAPTER XI. FORCING AND RETARDING PLANTS .... 157

Nature of the process. Retarding. Greenhouses and hothouses. Hotbeds. Cold frames. Forcing single hills. Etherization. Forcing plants in the window garden. Practical exercises.

CHAPTER XII. WEEDS 164

Definition of a weed. Harmfulness of weeds. Nature of weeds. Eradicating weeds. Purslane. Spreading amaranth. Green amaranth. Tumbleweed. Pigweed. Russian thistle. Spotted spurge.

CONTENTS • XV

PAGE

Dandelion. Plantain. Common bindweed. Black bindweed. Prickly lettuce. Ragweed. Wild mustard. Oxeye daisy. Canada thistle. Quack grass. Crab grass. Foxtail. Old witch grass. Buttercup. Wild carrot. Sorrel. Other weeds. Practical exercises.

CHAPTER XIII. PROPAGATION . . , 181

Natural methods. Typical forms for propagation. Artificial propagation. Cuttings. Hardwood cuttings. Layering. The sand box. Budding. Method of budding. Grafting. Different forms of grafting. Inarching. Grafting wax. Effect of stock on cion. Practical exercises.

CHAPTER XIV. DECORATIVE PLANTING 197

Purpose. Lawn making. Paths and lawn planting. Care of the lawn. The border. Arrangement of the plants. Shrubs for winter effects. Naming the shrubs and trees. Herbaceous plants. Arrangement of herbaceous perennials. Hedges. Bulbs. Carpet bedding. Formal planting. Transplanting shrubs and trees. Transplanting herbaceous perennials. Mulching and heeling in. Treatment of woodlands. Enemies of the forest. Practical exercises.

CHAPTER XV. PRUNING 216

Purpose of pruning. Time to prune. Pruning implements. Methods of pruning. Making the cut. Specimens needing little pruning. Pruning special crops. Thinning. Heading in. Root pruning. Girdling. Cavities and broken limbs. Topiary work. Practical exercises.

CHAPTER XVI. PLANT DISEASES 230

Origin. Number of plant diseases. Rots. Wilts. Blights. Leaf spot. Molds and mildews. Smuts. Rusts. Wound parasites. Other plant diseases. Sprays and spraying. Bordeaux mixture. Lime-sulphur wash. Ammoniacal copper carbonate. Potassium sulphide solution. Preventive measures. Practical exercises.

CHAPTER XVII. INSECT PESTS 246

How insects injure plants. Metamorphoses of insects. Forms of insects that cause injury. Cutworms. Cabbage worm. Currant worm. Tomato worm. Corn-ear worm. Tent caterpillar. Codlin moth. Curculio. Cankerworms. Borers. Elm-leaf beetle. Cucumber beetle. Blister beetles. Potato beetle. May beetles. Plant lice, or aphids. Squash bug. Mealy bug. Scale insects. Preventing attacks of insects. Poisons for chewing insects. Remedies against sucking insects. Spray pumps. Other aids in fighting insects. Practical exercises.

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PAGE

CHAPTER XVIII. PLANT BREEDING 258

Need for breeding. Basis for breeding. Inducing variation. Hybrids and hybridizing. Producing the cross. Mendel's law. Selection. Roguing. Xenia. Parthenogenesis. Practical exercises.

CHAPTER XIX. THE ORIGIN OF SPECIES 272

Evolution. Struggle for existence. Natural selection. Results of variation. Darwinian theory. Mutation theory. Practical exercises.

CHAPTER XX. OUR CULTIVATED PLANTS 277

Origin. Edible parts of plants. Root crops. Leaf crops. The legumes. Solanaceous fruits. Gourd fruits. The grasses. Bush fruits. Tree fruits. New fruits. Practical exercises.

Appendix

Seventy-five Shrubs Useful for Planting 286

Fifteen Woody Vines Desirable for Arbors and Porches . 288 Fifty Desirable Herbaceous Perennials 289

INDEX 291

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Chapter I

Chemical elements. The earth's crust, the animals and plants upon it, and the multitude of substances with which we are familiar are composed of a small number of simpler forms of matter, known as chemical elements^ combined in various ways. A chemical element may be defined as a substance that has not been resolved into simpler substances, and as thus defined there are only about eighty chemical elements in the world. Gold may be taken as an illustration. Though it be divided into particles too small to be visible in the microscope, or heated until it becomes liquid, or subjected to strong currents of electricity, it is still gold and nothing else. A few chemical elements may be found " native," that is, uncombined with others, but usually two or more unite to form chemical compounds. By far the larger number are always found thus combined. Oxygen may be cited as a familiar example of an element that exists both free and combined. As a free gas it forms about one fifth of the air we breathe ; combined with other elements it makes up about half of the water and rock of the earth's crust. Chemical elements are often grouped as metals and nonmetah^ the metals being greatly in the majority. Usually the metals may be distinguished by names ending in um. The difference between a metal and a nonmetal, however, is not easily defined. A

metal is supposed to have the following properties : it must exist as a solid and liave *a 'irietallic luster, must be capable of conducting heat and electricity, must be opaque, hard, malleable, ductile, and capable of forming compounds with oxygen. Probably no single metal has all these properties, but no substance would be accepted as a metal that did not possess many of them. Iron, nickel, copper, and mercury are among the more familiar metals. Carbon, sulphur, and phosphorus may be named as examples of the nonmetals. Theoretically, at least, each chemical element may exist as a solid, a liquid, or a gas, but many have not yet been produced in all three of these conditions. Increasing the temperature will make many of the ordinary solids liquid, and the reverse of this process, combined with pressure, serves to liquefy even the lightest gases. Water, while not a chemical element, will serve to illustrate this change of state. In its more familiar form it is a liquid, but if heated to 212° F. it becomes a gas, and if cooled below 32° F. it becomes a solid.

Atoms and molecules. An atom is the smallest part of a chemical element that can enter into combination with other parts. Atoms may therefore be said to be the units of which more complex compounds are built. Not very much is known regarding the size of atoms, but they are estimated to be about one hundred-millionth of an inch in diameter and to bear about the same relation to the size of a tennis ball that the latter bears to the earth. Atoms usually do not long exist as such, but combine with other atoms to form molecules^ which are the smallest enduring particles of a compound, just as the atoms are the smallest part of a chemical element. All the atoms of a single chemical element are exactly alike, otherwise it would not be a chemical element.

Chemical formulas. Atoms have the same relation to chemical compounds that letters have to words, and the chemist is therefore able to write a definite formula for the molecule of every substance. Each element has its own chemical symbol, usually the initial of its name, as C for carbon and P for phosphorus. When the initial is duplicated in the list of symbols, one more distinguishing letter may be added, as Ca for calcium and Pt for platinum. Occasionally an element may be given the initial of an older name, as in the case of K for potassium, where the initial stands for kalium. Iron has the symbol Fe, derived from ferrum. The student familiar with the names of the elements readily recognizes the kinds of atoms that form a given compound when its formula is read. When more than one atom of a kind enters into the combination, the number is written below the line and immediately following the symbol. Thus the formula CO^, representing a molecule of carbon dioxide, is seen to consist of one atom of carbon united with two atoms of oxygen. The molecule of water is written H^O. In this two atoms of

Table of the More Common Chemical Elements

Name

Symbol

Name

Symbol

Aluminum

Antimony (stibium) . .

Argon

Arsenic

Barium

Bismuth

Boron

Bromine

Calcium

Carbon

Chlorine

Cobalt

Copper (cuprum) . .

Fluorine . . . . . .

Gold (aurum) ....

Hydrogen

Iodine

Iron (ferrum) ....

Al

Sb

A

As

Ba

Bi

B

Br

Ca

C

CI

Co

Cu

F

Au

II I

Fe

Lead (plumbum) . . .

Lithium

Magnesium ....

Manganese ....

Mercury (hydrargyrum)

Nickel

Nitrogen

Oxygen

Phosphorus ....

Platinum

Potassium (kalium) . .

Silicon

Silver (argentum) . .

Sodium (natrium)

Sulphur

Tin (stannum) . . .

Tungsten (wolfram) Zinc

Pb Li Mg Mn

Hg

Ni

N

P

Pt

K

Si

Ag

Na

S

Sn

W

Zn hydrogen are joined to one of oxygen. When symbols in parenthesis are followed by a number written below the line, as Ca(N0g)2, it signifies that the elements and quantities in parenthesis are to be multiplied by the number so written. Calcium phosphate (C^^C^O^}^ would also be correctly written CagP^Og.

Chemical compounds. When salt and sand, or charcoal and sulphur, are stirred up together, the result is a mere mechanical mixture. In a chemical compound an entirely new substance is formed, which may possess characteristics quite unlike those of the combining elements. Under certain conditions charcoal and sulphur may be made to form a chemical union in which two atoms of sulphur join with one of carbon to produce carbon disulphide (CS^). Sulphur, as everybody knows, is a yellow solid and carbon a black solid, but the carbon disulphide formed by their union is neither black, yellow, nor a solid, but is a colorless liquid resembling water. Moreover, while either pure carbon or sulphur may be eaten without harm, when they are chemically combined they form a deadly poisonous liquid, which, exposed to the air, soon turns to a heavy, suffocating, and highly inflammable gas. Again, when carbon is burned in the air, as in ordinary wood and coal fires, one atom of carbon unites with two of oxygen and forms a colorless, suffocating gas known as carbon dioxide (CO^). In a similar way sulphur may be burned to form sulphur dioxide (SOg). Calcium carbide, from which acetylene gas is produced, is another union of carbon and is represented by the formula CaC^. It is interesting to note that all the chemical elements unite with others in definite and unvarying proportions. No matter how much oxygen may be present when carbon is burned, the molecule of carbon dioxide formed always consists of two atoms of oxygen and one of carbon. Carbon, however, may be made to form other combinations with oxygen. When there is a lack of oxygen, carbon monoxide (CO) may be formed. Some- elements, oxygen and carbon for instance, readily combine with a great many others, while some, like nitrogen and argon, are called inert, and only with difficulty can be made to unite with others. In chemical reactions heat is often evolved. A good illustration of this is seen in the heat that results from the union of oxygen and carbon when wood or coal is burned^ or when water is added to quicklime in the process of making mortar.

Distribution of the elements. The different elements are very unequally distributed. Some, like radium, are found in very minute quantities and always in combination with other elements, while others may form vast deposits which are nearly pure. Only about forty of the elements are at all common, while but five of these form 96 per cent of the planet on which we live. These five in the order of their abundance are oxygen, silicon, aluminum, iron, and calcium. Since the soil consists of particles from many kinds of rocks, it contains a considerable number of chemical elements, but only sixteen that are at all abundant, namely, oxygen, silicon, carbon, sulphur, hydrogen, chlorine, phosphorus, fluorine, aluminum, calcium, magnesium, potassium, sodium, iron, manganese, and barium.

Elements found in plants. Fifteen of the sixteen common chemical elements in the soil are found in plants. Of these, seven are metals and eight are nonmetals. In the first group are potassium, sodium, magnesium, calcium, aluminum, iron, and manganese ; in the second are oxygen, hydrogen, nitrogen, chlorine, carbon, phosphorus, sulphur, and silicon. Several of these are not regarded as essential to plant growth, as is also true of lithium, zinc, copper, boron, and fluorine, which are occasionally found in plants in certain regions. Some of the characteristics of the fifteen elements usually found in plants are given below.

Potassium (K) is a soft white metal, lighter than water. It quickly oxidizes or unites with oxygen when exposed to the air, and must be kept in oil or other substances that do not contain oxygen. It does not occur in the free state, but is always combined with other elements, as carbonates, sulphates, silicates, and chlorides. Potash is an oxide of potassium, and feldspar and mica consist largely of this element. Potassium is present in the ash of all plants, is found most abundantly in the growing parts, and is essential -to plant life.

Sodium (Na) is a soft, waxy, lustrous white metal much like potassium in appearance and always occurs combined with other elements. It oxidizes even in water and must be kept in fluids lacking oxygen. Its various combinations are abundant in the rocks. Sodium chloride (NaCl) is rock salt. What we commonly call soda is an oxide or carbonate of sodium. Chile saltpeter, or nitrate of soda, is largely used as a fertilizer. Sodium, while usually found in plants, is known to be nonessential, though it may take the place of potassium in neutralizing some of the acids formed in them. The chemical symbol is taken from natrium^ the name by which it was formerly known.

Magnesium (Mg) is a light, silvery white, moderately hard metal which is malleable but not very tenacious. It is not found native, but forms many compounds. It is permanent in dry air, but tarnishes in the presence of moisture. Burned in oxygen, it produces a blinding light and forms magnesium oxide (MgO), or magnesia. Dolomite and asbestos contain much magnesium, and Epsom salts is the sulphate of this element. Magnesium is found in most parts of the plant, but less abundantly than calcium, except in the seeds, where it is usually more abundant.