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EXPERIMENTAL PLANT PHYSIOLOGY FOR BEGINNERS BY LUCY E. COX B. Sc. LECTURER IN BOTANY AND NTfUKE STUDY AT QFAYSTOKE PLACE TRAINING COLLEGE, LONDON WITH ILLUSTRATIONS LONGMANS, GREEN AND CO. 30 PATERNOSTER ROW, LONDON FOURTH AVENUE 30TH STREET, NEW YORK BOMBAY, CALCUTTA, AND MADRAS AU rights reserved PREFACE IN this book the main physiological facts gf plant-life ire connected together by a series of simple experi nents, all of which can be carried out without the use of any elaborate apparatus. As far as possible the inferences obtained in the working of one experiment form the starting-point for the next. The book i intended essentially as a guide to practical work, and every experiment should therefore be care fully worked through, not merely reaci. The best plan for a teacher to follow, in all physiological work, is to present a problem to the children, and encourage them to suggest the method by which it may be solved and to draw their own conclusions from the observations made. By a Standing Order of the London County Council, it must be stated that the Council accepts no responsi bility for the opinions or conclusions given in this book. L. E. C. CONTENTS SECTION I PAGE THE FOOD OF THE PLANT . . . . . . 1 CHAPTER 1 I. THE COMPOSITION OK THE SOIL .... 1 II. THE ABSORPTION OF FOOD FROM THE SOIL . . 2 CHAPTER II I. THE COMPOSITION OF THE AIR .... 32 II. THE ABSORPTION OF FOOD FROM THE AIR . . 43 SECTION II THE BREATHING OF THE PLANT ..... 70 SECTION III THE GROWTH OF THE PLANT 81 INDEX 109 vii EXPERIMENTAL PLANT PHYSIOLOGY SECTION I THE FOOD OP THE PLANT CHAPTER I T. THE COMPOSITION OF THE SOIL Introductory, The fact that as a plant develops it increases in weight, is one that needsno demonstration. The oak tree is obviously heavier than the acorn from which it grows. This increase in weight must have been caused by absorption of food-material on the part of the plant. Now the only available sources from which a plant can absorb food are the soil and the air. It is necessary to determine, therefore, whether the plant takes in food from one or both of these sources, and, further, what is the nature of the food taken in. The Composition of the Soil. The soil is composed of grains formed from the breaking down of rocks, to getner with a varying amount of humus or decaying animal and vegetable matter. The particles are loosely held together, and the spaces between are filled with air and water. As a great many of the substances contained in the soil are soluble in water they pass into solution thus the water ceases to be pure and becomes a solution of various salts. An analysis of this solution is beyond the scope of this book, and we must be content to use the results given to us by chemists. A 2 EXPERIMENTAL PLANT PHYSIOLOGY . The following is a list of the more common salts dissolved in the water of the soil made up of sodium and chlorine. calcium, sulphur, and oxygen. magnesium, sulphur, and oxygen., , sodium, sulphur, and oxygen, chlorine, nitrogen, oxygen, phosphorus, 1 calcium, magnesium, and potassium. Common table salt, Gypsum Epsom salts Glaubers salts Traces of chlorides, nitrates, and phos phates of calcium, magnesium, and potassium From this list it appears that the substances present called by the chemist elements are sodium, chlorine, calcium, magnesium, sulphur, oxygen, nitro gen, phosphorus, and potassium. It must be remembered that these are the morecommon elements present in solution in the soil, but they are not the only ones that may be present for instance, the important element, carbon, is often there. It is a compound of carbon, calcium bi-carbonate, that causes the hardness of water in limestone districts. But, as it will be shown later, carbon compounds in the soil are not necessary for plant-life. A plant thrives just as well irk. a soil that contains no carbon as in one in which this element is present. In the soil, then, certain substances are present that are available as food...