Preface
The author has had in mind a two-fold purpose in the preparation of this book. First, it is hoped that it may serve as a text or reference book for collegiate students of plant science who are seeking a proper foundation upon which to build a scientific knowledge of how plants grow. The late Dr. Charles E. Bessey, to whom I owe the beginning of my interest in plant life, once said to me: "The trouble with our present knowledge of plant science is that we have had very few chemists who knew any botany, and no botanists who knew any chemistry." This may have been a slightly exaggerated statement, even when it was made, several years ago. But it indicated a very clear recognition by this eminent student of plants of the need for a better knowledge of the chemistry of plant cell activities as a proper foundation for a satisfactory knowledge of the course and results of plant protoplasmic activities. It is hoped that the present work may contribute something toward this desired end.
Second, the purpose of the writer will not have been fully accomplished unless the book shall serve also as a stimulus to further study in a fascinating field. Even the most casual perusal of many of its chapters cannot fail to make clear how incomplete is our present knowledge of the chemical changes by which the plant cell performs many of the processes which result in the production of so many substances which are vital to the comfort and pleasure of human life. Studies of the chemistry of animal life have resulted in many discoveries of utmost importance to human life and health. It requires no great stretch of the imagination to conceive that similar studies of plant life might result in similar or even greater benefit to human life, or society, since it is upon the results of plant growth that we are dependent for most of our food, clothing, and fuel, as well as for many of the luxuries of life.
The material presented in the book has been developed from a series of lecture-notes which was used in connection with a course in "Phyto-chemistry" which was offered for several years to the students of the Plant Science Group of the University of Minnesota. In the preparation of these notes, extensive use was made of the material presented in such general reference works as Abderhalden's "Biochemische Handlexikon" and "Handbuch der Biochemischen Arbeitsmethoden," Oppenheimer's "Handbuch der Biochemie des Menschen und der Tiere," Czapek's "Biochemie der Pflanzen," Rohmann's "Biochemie," Frankel's "Descriptive Biochemie," and "Dynamische Biochemie," Euler's "Pflanzenchemie," and Haas and Hill's "Chemistry of Plant Products"; as well as of the most excellent series of "Monographs on Biochemistry," edited by Plimmer, several numbers of which appeared in print prior to and during the period covered by the preparation of these lectures. Frequent use was made also of the many special treatises on individual groups of compounds which are mentioned in the lists of references appended to each chapter, as well as of articles which appeared from time to time in various scientific journals.
Hence, no claim is made of originality for the statements presented herein, except in an insignificant number of studies of enzyme action, and of the possible physiological functions of certain specific compounds. The only contributions which the writer has felt qualified to make to this general subject are those of an intense personal interest in the chemistry of plant processes and a viewpoint with reference to the relation of chemical processes to vital phenomena which will be apparent as the various subjects are presented.
The text has been prepared upon the assumption that the students who will use it will have had some previous training in elementary inorganic and organic chemistry. A systematic laboratory course in organic preparations, such as is required of students who are preparing to become professional chemists, is not at all a necessary requisite to the understanding of the chemistry of the different groups of plant compounds as here presented; but it is assumed that the student will have had such previous training as is now commonly given in a one-year collegiate course in "General Chemistry," or a year's work in general inorganic chemistry followed by a brief course in "Types of Carbon Compounds" or "Elements of Organic Chemistry," such as is usually required of students who are preparing for advanced work in agricultural science, in animal or human nutrition, etc.
An attempt has been made to arrange the material in such a way as to proceed from simpler chemical principles and substances to those of more complex structures. This results in an arrangement of the groups to be studied in an order which is quite different than their biological significance might suggest. It is believed, however, that in the end a more systematic understanding and a more orderly procedure is obtained in this way than would result from the treatment of the groups in the order of their relative biological importance.
CONTENTS
| [Introduction] | Page |
| Development of biological science; characteristics of protoplasm;plant and animal life, similarities and differences; protoplasmicactivity essentially chemical changes; objects of study of thechemistry of plant life | xiii-xvi |
| [CHAPTER I]—Plant Nutrients | |
| Definitions; the plant food elements; available and unavailableforms; the value of the different soil elements as plant foods;functions of the different plant food elements in plant growth;inorganic plant toxins and stimulants; references | 1-15 |
| [CHAPTER II]—Organic Components of Plants | |
| Plants as synthetic agents; types of changes involved in plantgrowth; groups of organic compounds found in plants; physiologicaluse and biological significance defined; physiologicaluses of organic groups | 16-20 |
| [CHAPTER III]—Photosynthesis | |
| Definitions; physiological steps in photosynthesis; formaldehyde,the simplest carbohydrate structure; the condensation offormaldehyde into sugars; theories concerning photosynthesis;the production of starches and sugars; references | 21-29 |
| [CHAPTER IV]—Carbohydrates | |
| Importance, nomenclature, and classification; groups of carbohydrates;isomeric forms of monosaccharides; chemical constitutionof monosaccharides; characteristic reactions ofhexoses; the occurrence and properties of monosaccharides;disaccharides; trisaccharides; tetrasaccharides; the relationof molecular configuration to biochemical properties; polysaccharides,dextrosans, levulosans, mannosans, and galactosans;physiological uses and biological significance of carbohydrates;references | 30-66 |
| [CHAPTER V]—Gums, Pectins, and Celluloses | |
| Relation to carbohydrates; groups; the natural gums and pentosans;mucilages; pectins; celluloses; physiological uses of celluloses; referencess | 67-75 |
| [CHAPTER VI]—Glucosides | |
| Definition; general structure; hydrolysis of the natural glucosides;general properties; the phenol glucosides; the alcohol glucosides;the aldehyde glucosides; the oxycumarin glucosides; the cyanophoricglucosides; the mustard-oil glucosides; the pigmentglucosides; the digitalis glucosides; the saponins; physiologicaluses; biological significance; references | 76-93 |
| [CHAPTER VII]—Tannins | |
| General properties; occurrence; chemical constitution; classes;some common tannins; physiological uses; biological significanceof tannins in fruits; references | 94-101 |
| [CHAPTER VIII]—Pigments | |
| Types and classes; the chlorophylls, chemical constitution, similarityof chlorophyll and hæmoglobin, properties of the chlorophylls;the carotinoids, carotin, xanthophyll, lycopersicin, andfucoxanthin; phycoerythrin and phycophæin; the anthocyans;the anthoxanthins; the production of ornamental pigments inflowers, etc.; the functions of pigments; references | 102-123 |
| [CHAPTER IX]—Organic Acids, Acid Salts, and Esters | |
| Chemical constitution; some common organic acids; physiologicaluses of organic acids; biological significance of fruit acids andesters | 124-128 |
| [CHAPTER X]—Fats and Oils, Waxes, and Lipoids | |
| General composition; fats and oils, occurrence, chemical constitution,acids which occur in natural fats, alcohols which occur innatural fats, hydrolysis and synthesis of fats, extraction of oilsfrom plant tissues, identification of fats and oils, physiologicaluse; the waxes; the lipoids, lecithin, other plant phosphatides,plant cerebrosides, physiological uses of lipoids; references | 129-145 |
| [CHAPTER XI]—Essential Oils and Resins | |
| Definitions, classes, occurrence; the essential oils; the resins;physiological uses and biological significance of essential oils;references | 146-150 |
| [CHAPTER XII]—The Vegetable Bases | |
| Composition and groups; the plant amines; alkaloids; the purinebases; the pyrimidines; the nucleic acids, composition anduses; references | 151-163 |
| [CHAPTER XIII]—Proteins | |
| Importance; general composition; amino-acids and peptid units;individual amino-acids; composition of the plant proteins;general properties of proteins; classification; differences betweenplant and animal proteins; extraction of proteins from planttissues; synthesis in plants; physiological uses; references | 164-180 |
| [CHAPTER XIV]—Enzymes | |
| Reaction velocities; enzymes as catalysts; general properties;extracellular and intracellular enzymes; chemical nature;nomenclature and classification; occurrence and preparation;general and individual enzymes; nature of enzyme action;accelerators and inhibitors; coenzymes and antienzymes;zymogens; physiological uses; further studies needed; references | 181-201 |
| [CHAPTER XV]—The Colloidal Condition | |
| "Colloids" and "crystalloids"; the colloidal condition a dispersionphenomenon; nomenclature and classification; conditionsnecessary to the formation of sols; gel-formation; generalproperties of colloidal solutions; suspensoids and emulsoids;adsorption; catalysis affected by the colloidal condition;industrial applications of colloidal phenomena; natural colloidalphenomena; references | 202-220 |
| [CHAPTER XVI]—The Physical Chemistry of Protoplasm | |
| Heterogeneous structure of protoplasm; protoplasm a colloidal gel;water; salts; osmotic pressure; surface boundary phenomena;electrical phenomena; acidity and alkalinity; summary; vitalphenomena as chemical and physical changes; references | 221-238 |
| [CHAPTER XVII]—Hormones, Auximones, Vitamines, and Toxins | |
| External and internal stimulants; hormones; vitamines; auximones,toxins | 221-238 |
| [CHAPTER XVIII]—Adaptations | |
| General discussion; adaptations, accommodations, and adjustments;chromatic adaptations; morphological adaptations; accommodations;concluding statements | 249-258 |
| [Index] | 259-268 |
INTRODUCTION
The history of biological science shows that the conceptions which men have held concerning the nature of plant and animal growth have undergone a series of revolutionary changes as the technique of, and facilities for, scientific study have developed and improved. For a long time, it was thought that life processes were essentially different in character than those which take place in inanimate matter, and that the physical sciences had nothing to do with living changes. Then, too, earlier students had only vague notions of the actual structure of a living organism. Beginning with the earliest idea that a plant or an animal exists as a unit organism, to be studied as such, biological science progressed, first to the recognition and study of the individual organs which are contained within the organism; then to the tissues which make up these organs; then (with the coming into use of the microscope as an aid to these investigations) to the cells of which the tissues are composed; then to the protoplasm which constitutes the cell contents; and finally to the doctrine of organic evolution as the explanation of the genealogy of plants and animals, and the study of the relation of the principles of the physical sciences to the evolutionary process. The ultimate material into which organisms are resolved by this process of biological analysis is the cell protoplasm. But protoplasm is itself made up of a complex system of definite chemical compounds, which react and interact according to the laws of physical science. Hence, any study of the chemistry of plant growth is essentially a study of the chemical and physical changes which take place in the cell protoplasm.
Protoplasm differs from non-living matter in three respects. These are (1) its chemical composition; (2) its power of waste and repair and of growth; and (3) its reproductive power. From the standpoint of chemical composition, protoplasm is the most complex material in the universe. It not only contains a greater variety of chemical elements, united into molecules of enormous size and complexity, but also a greater variety of definite chemical compounds than exist in any other known mixture, either mineral or organic in type. One of the first problems in the study of protoplasm is, therefore, to bring this great variety of complex compounds into some orderly classification and to become familiar with their compositions and properties. Again, living matter is continually undergoing a process of breaking down as a result of its energetic activities and of simultaneously making good this loss by the manufacture of new protoplasm out of simple food materials. It also has the power of growth by the production of surplus protoplasm which fills new cells, which in turn produce new tissues and so increase the size and weight of individual organs and of the organism as a whole. Hence, a second field of study includes the chemical changes whereby new protoplasm and new tissue-building material are elaborated. Finally, living material not only repairs its own waste and produces new material of like character to it, but it also produces new masses of living matter, which when detached from the parent mass, eventually begin a separate existence and growth. Furthermore, the plant organism has acquired, by the process of evolution, the ability not only to produce an embryo for a successive generation but also to store up, in the tissues adjacent to it, reserve food material for the use of the young seedling until it shall have developed the ability to absorb and make use of its own external sources of food material. So that, finally, every study of plant chemistry must take into consideration the stored food material and the germinative process whereby this becomes available to the new organism of the next generation. Also, the chemistry of fertilization of the ovum, so that a new embryo will be produced, and the other stimuli which serve to induce the growth phenomena, must be brought under observation and study.
A further step in the development of biological science has been to separate the study of living things into the two sciences of botany and zoology. From the standpoint of the chemistry of the processes involved this segregation is unfortunate. It has resulted in the devotion of most of the study which has been given to life processes and living things to animal chemistry, or "physiological chemistry." As a consequence, biochemistry, which deals with the living processes of both plants and animals, is yet in its infancy; while phytochemistry is almost a new science, yet its relation to the study of plants can scarcely be less vital than is that of physiological chemistry to studies of animal life.
The common conception that plant life and animal life are antithetical or complementary to each other has much to justify it. Animals breathe in oxygen and exhale carbon dioxide; while plants use the carbon dioxide of the air as a part of the raw material for photosynthesis and exhale oxygen. Plants absorb simple gases and mineral compounds as raw food materials and build these up into complex carbohydrates, proteins, fats, etc.; while animals use these complex compounds of plant origin as food, transforming parts of them into various other forms of structural material, but in the end breaking them down again into the simple gases and mineral compounds, which are expelled from the body through the excretory organs. Thus it would seem that the study of the chemistry of plant life and of animal life must necessarily deal with opposite types of phenomena.
But one cannot advance far into the study of the biochemistry of plants and animals before he discovers marked similarities in the chemical principles involved. Many of the compounds are identical in structure, undergo similar changes, and are acted upon by similar catalysts. Plant cells exhibit respiratory activities, using oxygen and giving off carbon dioxide, in exactly the same way that animal organisms do. The constructive photosynthetic processes of green plants are regulated and controlled by a pigment, chlorophyll, which is almost identical with the blood pigment, hæmatin", which regulates the vital activities in the animal organism, differing from the latter only in the mineral element which links the characteristic structural units together in the molecule. Many other points of similarity in the chemistry of the life processes of plants and animals will become apparent as the study progresses. It is sufficient now to call attention to the fact that these vital processes, in either plants or animals, are essentially chemical in character, and subject to study by the usual methods of biochemical investigations.
The protoplasm of the cell is the laboratory in which all the changes which constitute the vital activities of the plant take place. All of the processes which constitute these activities—assimilation, translocation, metabolism, and respiration—involve definite chemical changes. In so far as it is possible to study each of these activities independently of the others, they have been found to obey the ordinary laws of chemical reactions. Thus, the effect of the variations in intensity of light upon photosynthesis causes increase in the rate of this activity which may be represented by the ordinary responses of reaction velocities to external stimuli. Similarly, the effect of rises in temperature upon the rate of assimilation and upon respiration are precisely the same as their effect upon the velocity of any ordinary chemical reaction. Within certain definite ranges of temperature, the same statement holds true with reference to the rate of growth of the plant, although the range of temperature within which protoplasm lives and maintains its delicate adjustment to the four vital processes of life is limited; beyond a certain point, further rise in temperature does not produce more growth but rather throws the protoplasmic adjustment out of balance and growth either slows up markedly or stops altogether.
Hence, we may say that the methods by which the plant machine (protoplasm) accomplishes its results are essentially and definitely chemical in character and may be studied purely from the standpoint of chemical reactions, but the maintenance of the machine itself in proper working order is a vital phenomenon which is largely dependent upon the external environmental conditions under which the plant exists. A study of the phenomena resulting from the colloidal condition of matter is throwing a flood of light upon the mechanism by which protoplasm accomplishes its control of vital activities. But we are, as yet, a long way from a complete understanding of how colloidal protoplasm acquires and maintains its unique ability of self-regulation of the conditions necessary to preserve its colloidal properties and of how it elaborates the enzymes which control the velocity of the chemical reactions which take place within the protoplasm itself and which constitute the various processes of vital activity.
The object of this study of the chemistry of plant growth is to acquire a knowledge of the constitution of the compounds involved and of the conditions under which they will undergo the chemical changes which, taken all together, constitute the vital processes of cell protoplasm.