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BOTANY AS AN EXPERIMENTAL SCIENCE IN LABORATORY AND GARDEN OXFORD UNIVERSITY PRESS AMEN HOUSE, E.C. 4 London Edinburgh Glasgow New York Toronto Melbourne Capetown Bombay Calcutta Madras Shanghai HUMPHREY MILFORD PUBLISHER TO THE UNIVERSITY hy ie d h i ip : f BOTANY AS AN EXPERIMENTAL SCIENCE IN LABORATORY AND GARDEN By LILIAN J. CLARKE D.Sc. (Lonp.), FS. FORMERLY HEAD OF SCIENCE DEPARTMENT JAMES ALLEN’S GIRLS’ SCHOOL, DULWICH OXFORD UNIVERSITY PRESS LONDON : HUMPHREY MILFORD 1935 ‘In my laboratory I find that water of Lethe which causes that I forget everything but the joy of making experiment.’ ROBERT BOYLE ‘In a great variety of articles very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.’ JOSEPII PRIESTLEY, 1774 PRINTED IN GREAT BRITAIN PREFACE OTANY at the James Allen’s Girls’ School for many years has been taught by means of observations and experiments made by the girls themselves in laboratory and garden. No text-books are used until post-Matriculation work is reached. The girls make their own books, and in them are re- corded not only the results of their own experiments, but the results of hundreds of other experiments made during the course of many years. It is wrong in biological work, as in other branches of science, to generalize from a few facts. Professor Bateson, in the Huxley Centenary number of Nature said: ‘No one better than Huxley knew that some day the problems of life must be investigated by the methods of physical science, if biological speculation 1s not to degenerate into a barren debate.’ Of biological science Huxley said: “The subject-matter 1s different from that of other sciences, but the methods of all are identical; and these methods are: 1. Observation of facts, including experiments. 2. Comparison and classification, the results of the process being named: GenéreMPFspositions. 3. Deduction. 4. Verification. Such are the methods of all science whatsoever.’ The time allotted to a lesson at J.A.G.S. is often short, but if the results of experiments are recorded, year after year, there can be accumulated a mass of evidence to which reference can be made. But the reference should not be made until after the members of a class have made their own experiments, and the results have been summarized. In this way there can be a training in scientific method as well as a discovery of facts. There is the training in manipulation, in recording results, in comparing individual results with those obtained by others, and in drawing conclusions from a great number of facts. Any results which differ from the majority are not slurred over, but carefully examined, and possible explanations of the dis- crepancies are often suggested by the girls themselves. vi PREFACE There are recorded at J.A.G.S. the results of more than 4,000 experiments made to see if pollen is necessary for the for- mation of fruit. The leaves of more than 350 species have been tested to see if they form starch in the light, and nearly 300 experiments have been made to see if there are pores in leaves, and if so, how they are distributed. Since the end of last century more importance has been paid at the James Allen’s Girls’ School to the plant as a living organism than to any other branch of Botany. As a rule the experiments are made by the girls themselves, every girl, either alone, or with a partner, setting up and carrying out the experi- ments in the laboratory or garden. The only exceptions to this in pre-Matriculation classes are those experiments involving the use of a clinostat or auxanometer, and those showing the respiratory coefficient, anaerobic respiration, and the growth of the root into mercury. It must be remembered, however, when examining the results of experiments, that these experiments have been made by young inexperienced girls, often with very simple apparatus, and that the time in which to make the experiments 1s strictly limited, the longest unbroken period being one hour twenty minutes 1n the School Certificate form and the form below it. It is impossible for the teacher to verify all results in a short lesson, but it is good for pupils to have responsibility, and to feel the recorded results must depend on their own unaided work. It has been found that the fact that they were helping to build up the school records does appeal to the girls’ sense of responsibility. An objection has been made that this experimental method demands more time than is usually allotted. At Dulwich an unusual amount of time has not been given to Botany. ‘The ex- periments on pollination, for example, were for many years done by girls who had only one lesson of one hour per week for Botany, and in earlier days still, by classes of forty girls who had only forty minutes. The experiments could only be made on fine days in the summer term, and only part of the time could be given to the experimental work. Great stress is laid on control experiments, the necessity for which is readily appreciated by the girls, and arouses their critical faculties. The experimental method of studying Botany has been greatly PREFACE vil helped by the development of Botany Gardens. The gardens have been made gradually in response to the needs of the work. They have become, in many cases, out-of-door laboratories, and the work indoors and out of doors is one. The gardening work itself is voluntary and always has been, but there has never been a lack of volunteers. In the laboratory, in classes up to and including the School Certificate examination class, the compound microscope is not used, except in studying a green alga, such as Spirogyra, and the minute structure of a leaf. Much can be seen with the aid of a good hand-lens, for example, in a piece of wood. The structure in sections of dicotyledonous stems, monocotyledonous stems, lenticels, maize grains, and the mouth parts of insects mounted whole, show well, viewed by a magnifying glass in a special slide holder. Malpighi made his classical discoveries with a simple microscope no better than a half-crown lens of the present day. He was the first to observe the capillaries (1661), he made the earliest anatomical study of an insect (1669), and he demon- strated the nature of the tissues of many animals and plants. Records. The keeping of records goes on steadily year after year. It was difficult to keep many in the early years (1896-1912) when the gardens were being made and there was no grant, little assistance, and the work had to be done in out-of-school hours. This book deals with experimental and ecological work. For want of space the accounts of many experiments have bcen omitted. Other branches of the work, such as morphology and classification, are not included. With a few exceptions the work described is the work of the pre-Matriculation or School Certificate classes, and not the more advanced work. H.M.I. Dr. Wager, F.R.S., on the occasion of his last visit of inspection to the James Allen’s Girls’ School, urged me to write a book giving an account of the work in Botany initiated and developed by me at the school, and include in it records of experiments. My warmest thanks are due both to Professor V. H. Black- man, F.R.S., Professor of Plant Physiology at the Imperial College of Science, for reading Chapters I to VI (Experiments vill PREFACE in the Laboratory), and to Professor Tansley, F.R.S., Sherardian Professor of Botany, Oxford, for reading Chapters VII to XIV (the Botany Gardens), and for their most valuable suggestions. Also to Professor ‘Tansley for the kindly interest he has taken for years in the Botany Gardens. I am greatly indebted to Miss ‘Talbot, B.Sc., second Botany Mistress 1912 to 1916, and my successor from 1926 to 1931, the last date up to which the selected records have been taken. Miss Talbot has given constant help throughout the writing of this book. All the diagrams have been made by ‘old girls’. Many more would have lked to help if they had been easy of access. My thanks are duc to those who have made the diagrams, and to the great number of ‘old girls’ without whose help the Botany Gardens could not have been made or maintained. LILIAN J. CLARKE. 3, BISIIOP’S COURT, EAST FINCHLEY, N.2. CONTENTS EXPERIMENTS IN LABORATORY CHAPTER I SEEDS AND SEEDLINGS . . . . . I Experiments to see if seeds will germinate (1) in oxygen, nitrogen, carbon dioxide, (2) at various temperatures. Reserve substances in seeds. Tests for starch, proteins, oils. Action of diastase on starch. Absorption of water by roots, experiments to see if plants can absorb solids, path of water in roots and stems. Growth of seedlings in light and absence of light. Effect of brief light exposure on ctiolated seedlings. CHAPTER II PHOTOSYNTHESIS . . . . . . 8 Production of starch. Green leaves from 416 plants of different specics tested for starch. Summary of records of experiments. Many results checked by microscopic examination of Icaf sections by elder girls. Tests for sugar when no starch found. Conditions necessary for production of starch. Evolution of oxygen. Records of experiments. CHAPTER III FOOD OF PLANTS . . . . . 16 Constituent elements of plants found by analyses. Essential elements determined by growth of plants in various culture solutions. Generations of plants in culture solutions. Summary of thirty years’ experience in water-cultures. CHAPTER IV TRANSPIRATION . . . . . » 22 Liquid tested. Results of experiments on 298 plants to sce if pores are present in leaves, and distribution of pores if present. Strips of epidermis under microscope. Minute structure of leaf. Comparison of rates of transpiration from upper and lower surfaces of leaves. Potometer. Comparison of rates of absorption and transpiration. Weight of water lost in transpiration. Rate of transpiration under varying conditions. RESPIRATION . . . . . . 28 Experiments to see what gas is given off, what gas is taken in. Comparison of volumes. Production of heat. Records of experiments. Anaerobic respiration. 4158 b x CONTENTS CHAPTER V GROWTH IN PLANTS . . » 35 Experiments showing distribution of growth i in roots and stems. Graphs. Measurement of growth in length. DIRECTION OF GROWTH . . . 39 Experiments showing influence of presence of watcr, light, and gravity. Growth of plants on a clinostat. Perception of gravity in a root. CHAPTER VI THE SOIL . . . . . . . 48 Determination of percentages of (a) water lost when soil is air-dried, (b) water present in air-dried soil. Mechanical analysis of a soil. Sand and clay compared as to the rate at which (1) water passes up, (2) air passes through. Water capacities of soils. Determination of percentage of humus in various soils. Factors influencing temperature of soils (colour, aspect). THE BOTANY GARDENS CHAPTER VII HISTORY AND ORGANIZATION 55 Begun 1 in 1896. No grant for fifteen years. Grant from Board of Educa- tion in 1912. Out-of-school voluntary work in a day school. Organiza- tion. Use of tools. Visitors from many countries. Subjects of theses in Spain, France, Sweden. School Botany Gardens made elsewhere. Study of animals. Biology gardens. CHAPTER VIII POLLINATION EXPERIMENTS . . . . 60 Experiments (a) to find the function of pollen (records of 4,000 experi- ments), (5) to see if self-pollination can take place in various plants (6,000 experiments). Experiments on pollination of primrose. Records of insects seen visiting flowers. CLIMBING PLANTS . 71 Plants in garden, in class-room, and in laboratory. Experiments showing rates of revolution, influence of thickness of support, and angle of in- clination of support. Effect of inversion, growth on a clinostat, and absence of light, on twining stems. CHAPTER IX THE LANE 75; Construction. Cost. Study of plants in spring, summer, winter. Tendril climbers. Determination and comparison of degrees of sensitiveness of tendrils. Influence of aspect on time of flowering of plants. Influence of aspect on soil temperatures. Animal life in the Lane. Plants of the J.A.G.S. Lane. CONTENTS xi CHAPTER X THE PONDS . . 82 (a) Large pond. Construction. Cost. Water supply. Drainage. Fresh- water marshes. (b) Smaller pond for little plants crowded out in larger pond. Con- struction. List of plants in J.A.G.S. ponds and marshes. Great vegetative reproduc- tion. Plants to avoid. CONDITIONS UNDER WHICH WATER PLANTS LIVE . 89 Comparison of maximum and minimum temperatures in pond and in air above pond. Study of animal life in ponds. CHAPTER XI THE HEATH . . . - 93 Construction. Soil from a Surrey heath. List of plants in J.A.G.S. heath. THE BOG . . , . 96 Large one in heath. Construction. Peat from Lancashire. Cost. List of plants in J.A.G.S. bogs. CHAPTER XII SAND DUNES _. . . . 99 Construction. Cost. Colonization of big sand dune by a sand-sedge plant. Vegetative reproduction. List of plants in J.A.G.S. dunes. SALT MARSHES . . . . . . IO! Soil obtained from two sources. Experiments to ascertain suitable strength of salt solution to be poured on marshes. Quantity of salt solution given in one year. Particulars of research work done by an ‘old girl? on J.A.G.S. salt marsh. Material for other research at present time. List of plants in J.A.G.S. salt marshes. PEBBLE BEACH . . . . . . 104 Pebbles from Brighton. Cost. Imitation of nature in covering up plants with pebbles, and in providing seaweed (‘drift’) for beach. List of plants in J.A.G.S. pebble beach. CHAPTER XIII CORNFIELD , , , ; . . . 107 (a2) Small and large. (b) Plots of wheat, barley, oats, rye. Weeds of the cornfield. MEADOW. Dominant grasses. List of plants . . . 108 xii CONTENTS CHALK BEDS. Construction. List of plants . . . 10 THE WALL. Construction. List of plants . . . Iii VARIATION . . . . . . . 112 STRUGGLE FOR EXISTENCE . . . . . «12 MENDELIAN EXPERIMENTS . . . 113 Actual results in F, generation compared with theoretical results. SOIL EXPERIMENTS _. . . , . . EIS MANURIAL EXPERIMENTS _. , ; . 116 Recent experiments on mustard. Advice from Rothamsted Experimental Station. Plots treated with complete artificial manure, manure lacking phosphate, &c. CHAPTER XIV THE WOODS . . . . . . . 19 Consideration of soil. Damp oakwood the type chosen. 783 oaks (Quercus robur) planted. Competition of woodland plants and ‘weeds’. Age at which acorns were borne. Birds’ nests. ‘Thinning of trees. Plant diseases. Changing conditions in the wood: (a) humus content, (bd) evaporating power of atmosphere, (c) light intensity. List of trees, shrubs, and herbs in J.A.G.S. wood. APPENDIX . . . . . . . 132 INDEX . . . . . . . . 137 NOTE P. 115, F, Generation. ror Purple flowers read Coloured flowers