Ei. ALBERT R. MANN LIBRARY NEw YorK STATE COLLEGES OF AGRICULTURE AND HomME EcoNoMICs AT CORNELL UNIVERSITY Cornell Univ “mpaical Investigations upon the germ; Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924000502561 ECOLOGICAL INVESTIGATIONS UPON THE GERMINATION AND EARLY GROWTH OF POREST TREES BY BICHARD EH. BOERKER A THESIS PRESENTED TO THE FACULTY OF THE GRADUATE COLLEGE IN THE UNIVERSITY OF NEBRASKA IN PARTIAL FULFILLMENT OF REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF BOTANY LINCOLN, NEBRASKA JANUARY I, I916 cd I—ECOLOGICAL INVESTIGATIONS UPON THE GERMINATION AND EARLY GROWTH OF FOREST TREES BY RICHARD H. BOERKER CONTENTS Pace Pretatory INO: ee patyeisswnis wstn acdsee nae dain ssndd Aaa detuantuadeneonens I Brelitititiatys (COmsi Cena trons + ccs 4 avsletatlsatiagmayavdaieeo os nob Saints tenteastdhip ebbnswevdntcontas Gp TET YS EO MeL Calls” ayn avs oNearagscan osieae sel bre reenentvon esc nipsen ec uau chart ey aaa a dee i 7 Classification and Résumé of Habitat Factors .............0..00008 II dhe: Germination, (PRocess .42.0eyacsummaewmnneen ere earaiines I5é Method of Attacking Problem at Hand. ......0...02¢scaseees ewan 19 Methods: atid Apparatts USE oc scdcscccsssuasevscacens.td.acbeaiiniaid eusnaradendudreatunass 2I THe: (Control iOr sbabitat: HACtSES! a savassicua evondetesss dtm td a ota sueebveadonnbaaveed san 24u INotés: om Dampinesot acaswccagnctiavnmnmgeewa qoayenenmnmitaerrnannte 32 The Effect of Habitat Factors upon Germination .........0.ees0eee 34 The Effect of Habitat Factors upon Stem and Root Development .... 64% The Relation of Size and Weight of Seed to Germination Per Cent. atic. Hately DEVELO pie Tt 6 sca wcxinladeincaunaxtartecnsunudsinanichos ayadeotaancneptuterraingdacaas 70’ Summary of ConmcluSions: -aiwwscia nas aarasiesneacs einen tenes apt annecnauirinctoecieeitse 82° Bibliography”. vaeransniennenae sy oeeerogeareres wes tacwienenaanearseeas 88 PREFATORY NOTE Almost every national industry makes provision for investiga- tive work. Millions of dollars are spent annually to develop both human and mechanical efficiency. It is immaterial whether the investigations are for the purpose of utilizing certain products hitherto considered waste, or to make workmen more efficient, or to employ the latest processes and inventions to better survive in the competitive struggle—the results of this class of work are I 2 Richard H. Boerker considered a great, indispensable business asset, warranting whole- some moral and financial support. The history of our country reveals the fact that material in- dustrial progress is largely in direct proportion to scientific re- search and invention. This is especially true in the agricultural pursuits. The various governmental bureaus, our state universi- ties and agricultural colleges, and our many agricultural experi- ment stations are intimately connected with and responsible for the progressive agricultural development of our country. These institutions form a vast ganglionic intellectual organization ; they are rapidly becoming the centers of a new agricultural system and, working from these centers outward, they are gradually touching every phase of agricultural activity. Forestry has joined the ranks of the great industries in develop- ing the investigative side of the business and the establishment of forest experiment stations and a forest products laboratory by the Forest Service of the United States Department of Agri- culture has been the first step in this direction. It has become the business of these stations and this laboratory to study the funda- mental laws governing the life of the forest and their effect upon the final product—wood. That vast complex of environmental factors—the habitat—is beginning to be analyzed to discover in what ways man can help nature to produce more and better timber, in a shorter length of time and at less cost than nature has produced in the ages past. While perhaps, on account of economic conditions, industrial investigations have been given preference to purely silvicultural research, yet investigations in establishing and growing forests have received no small amount of attention. Outside of these governmental endeavors very little has been done along the lines of silvicultural research. State forest ex- periment stations are practically unknown. It is true that the foresters as well as the ecologists connected with some of our agricultural experiment stations are contributing to this field, but a beginning has scarcely been made. There is a great need for state forest experiment stations or at least for foresters upon the staffs of some of the agricultural experiment stations to help Germination of Forest Trees 3 solve local forestry problems. Finally, there is no reason why forest experiment stations established and maintained by private endowment on the plan of the Desert Botanical Laboratory of the Carnegie Institution would not be able to do a great service be ee lines. al The importance and need of silvicultural investigations scarcely needs comment, yet it might be well at the outset to emphasize certain fundamental concepts. Forests are one of our greatest natural resources. Unlike coal, iron, oil, etc., they can be grown to insure a continuous supply. Forests are not huge warehouses of standing logs from which we can take our annual Supply ad infinitum, they are not merely aggregations of indi- vidual trees; they are complex communities of living organisms capable of response to environmental factors not unlike hiwman beings. It follows then that in order to replace what we take from the forest, in other words, in order to grow a neverfailing supply of timber_intelligently and economically, we must under- stand these complex living organisms and commutiities, must study their behavior and requirements and ascertain the condi- tions under which they grow best. This domain is forest ecology or silvics. It has been asked, Does forestry in its present stage of develop- ment need this kind of work? Is not this work ahead of the times? Is it not of too little practical value to demand our atten- tion at present? It will be my purpose to show at this point of my paper that, while this class of work is not absolutely essential to forestry at the present time, it is extremely desirable that it be begun in a scientific manner at the earliest possible moment, in order to put American forestry upon a firm scientific basis. The present status of forestry in the United States em- phasizes the necessity of beginning soon. A brief word as to our present stage of development may be in order. Forestry either of an intensive or an extensive nature is being practised in many parts of the country to-day. Both private and public corporations are engaged in one or more of the main phases of it, viz.: silviculture, forest protection, forest administration, or forest utilization. In the field of forest protection gigantic 4 Richard H. Bocrker strides have been made in the last ten years on both public and private holdings, and obviously this is the first step towards forest management. Such intensive silvicultural operations as planting and thinning are being practised principally in the east, while ex- tensive forestry involving the selection and shelterwood systems of management is almost the rule in the west. As might be expected, in the west forest planting is still in its experimental stage. On the whole economic conditions in the east have favored the development of both public and private forestry and hence this activity has been on a more intensive scale there than in the west. That forestry in some sections of the country is not de- veloping as fast as some conservationists might wish is due to the fact that it is being held back by certain conditions and elements of environment which by their very nature belong to a new country with enormous natural resources like ours and over which human endeavor has no control. It must be realized that forestry never developed in any country in the world as fast as it has in the United States in the last twenty-five years, and that at the present time it is proceeding as fast as is consistent with sound principles and existing economic conditions. While the practice of forestry is making rapid strides, silvi- cultural investigations are still in the infancy of their develop- ment. In other words the practice of forestry and the science of forestry have not developed in a ratio which would make them mutually helpful. The greater development of the applied phases of forestry is due partly to economic conditions and partly also to a lack of appreciation of the value of purely scientific research. The tendency has always been to magnify the industrial branch of a science at the expense of the main body from which it had its origin. Purely scientific botany has been largely lost sight of in the face of such of its branches as bacteriology, plant breeding, pathology, etc. Similarly the science of silvics has had to give way to seemingly more important phases concerned with the utilization of forests. In these days of commercial ideals when the value of most things is gauged by what they will bring on the market, I fear that undue emphasis has been placed upon the economic or applied phases of a science. Hence it is not strange Germination of Forest Trees 5 that we should measure the value of purely scientific work in dollars and cents rather than in terms of scientific advance and intellectual satisfaction. The test nowadays applied to any sci- ence by the large majority of people is, How much money does it influence? What industries has it created? What has it added to the wealth of the world? If purely investigative work in forestry must give a raison d’étre, it might be well to call to mind the following facts: that many of its problems strike the foundations of national pros- perity and their value cannot be measured in dollars and cents; that some of its problems must be gauged by the future returns they bring rather than by the present; and that it is the avowed purpose of scientific work to solve those problems in which the so-called practical worker has failed to produce results. History bears witness to the fact that those fields which have seemed furthest removed from utility have often yielded the most fruitful results. What seems of only scientific value to-day very often turns out to be of great practical utility later. It is comparatively easy to estimate the value of a piece of work when it is possible to base that estimate upon what has been actually gained; but how hopeless is very often the task when we must base our esti- mate upon the loss which it prevented. In such silvical investiga- tions as the influence of forests upon stream flow, upon the water supply of communities, and upon the health and prosperity of our people money values fade into insignificance. Silvicultural investigations as well as forestry business are long time propositions. The value of such work is very often measured not so much by the immediate financial returns it brings as by the principles it helps to establish, which in turn may affect our management and hence the financial returns many years hence. It is the time element more than any other that em- phasizes the need for beginning the solution of some of our silvi- cultural problems soon. It is believed by many that it will be at least twenty-five years before intensive operations such as plant- ing, thinning, and other silvicultural measures will be economically possible in some parts of the country. Granted that this is true. Is this too much time to devote in preparation for this work? If 6 Richard H. Boerker we keep on getting results in the next twenty-five years in the same proportion as we have done in the past ten, will many of our important problems be solved? Most silvicultural investigative problems take many years to solve. Some nursery and planting problems can be solved in from three to five years (if nothing interferes), but most of even these take longer. In many cases it takes from two to four years merely to raise stock let alone experiment with it. It usually takes six months or more to de- termine whether the stock set out will live, let alone establish principles in planting. The element of time is the largest factor in this work ; we will need much of it, for failures will be numer- ous and this will mean the loss of many years. Only long time and carefully planned investigations can lead to stable and eco- nomic forest management. With the development of forestry it cannot be doubted that a great deal of exact silvical and silvicultural knowledge is neces- sary, and we must admit that a great deal of data is needed to-day which cannot be furnished. We have unsystematic and indefinite knowledge about many phenomena which await experimental proof. In fact, forestry is loaded down with a vast weight of undigested facts, and pure science has only begun to relieve forestry of this burden. The quickest and surest way for purely forestry research to gain recognition is to show how to attain practical results which years of blind groping along applied lines have failed to accomplish. Our task is a gigantic one, greater than any investigative prob- lems that have confronted or will confront European nations. We have more species of trees important in forestry than all European nations combined. Our varied topographic and cli- matic conditions make our problems infinitely more complex and numerous. But that should not discourage us. Big problems concerning the forest have been solved in the past and are being attacked to-day. We have worked out our problems in logging and have developed machinery and methods unique in the history of forest industry; we have developed a system of forest fire protection unlike anything ever attempted by forestry-practicing nations ; it remains for American ingenuity and enterprise to solve the silvicultural problems which confront the American forester. Germination of Forest Trees 7 Briefly stated the purpose of the present investigation is to inquire into the effect of the more important habitat and seed factors upon the germination and early development of certain American forest trees in control cultures in the greenhouse for the purpose of obtaining data that may be used in the silvicultural management of these species. This investigation has been conducted under the direction of Professor Raymond J. Pool and I am indebted to him for his friendly advice and counsel. I am especially grateful to him for having read the first draft of this paper and for offering valuable criticisms and suggestions. I wish to further acknowledge my indebtedness to Professors P. B. Barker and H. J. Young of the department of agronomy of the College of Agriculture for the mechanical analyses of the soils used in these experiments and to various members of the departments of botany and geology for the many courtesies extended to me. Thanks are due to the various district foresters, forest supervisors, and rangers, also members of the Washington office of the Forest Service for their kindness in furnishing so much of the seed used in these investigations. Without this material assistance a large part of this work would have been impossible. Grateful acknowledgment is also due to my wife for much valuable assistance in counting seeds, in com- piling the final data and in reading proof. Also, I cannot fail to acknowledge the guidance and inspiration of the late Dr. Charles E. Bessey throughout the course of these studies. PRELIMINARY CONSIDERATIONS Historical The literature of the work done upon this problem is meager and widely scattered. As has been noted before, both botanists and foresters have worked in this field, so that papers from widely different sources had to be considered. General observa- tions were found to be much more numerous than results based upon exact investigations. Too often one finds opinions and views upon these questions with but very little data to substantiate 8 Richard H. Boerker them. Foresters and botanists, in general, have proceeded on the assumption that light and soil moisture are necessary for germination. They have also noted that germination is acceler- ated in sand as against a heavier soil like loam or clay. Little has been done to inquire further into these relations. On the whole the effect of habitat factors upon the early development of plants has received more attention than their effect upon germina- tion. In the following historical summary, light in relation to germination and early development of plants will be considered first, since probably more work has been done upon that particular phase of the problem than any other. One of the oldest notions regarding light and its relation to plant growth is the one concerning the effect of artificial or natural shade upon atmospheric and soil moisture conditions. The forest experiment stations of Europe have long since worked out this relation in the forest, so that to-day these results are more or less well known to all foresters and botanists. Several Americans, working on the effect of artificial shading upon the growth of tobacco, have brought out results similar to those secured in connection with forests. Hasselbring (3) has shown that the transpiration of plants grown in the open is nearlv 30 per cent. greater than the transpiration of plants grown under cheese-cloth shade. The transpiration per unit of leaf surface was nearly twice as great in the sun plants as in the shade plants. Stewart (4) records the results of observations made in the course of tobacco experiments in Connecticut on the climate and soil conditions as affected by tents in producing a certain kind of tobacco. He concludes that under the shade of tents the soil retains more moisture, there is a greater relative humidity, and there is a reduction in wind velocity, all resulting in plants which are larger and of more rapid growth as compared to those grown without tents. To sum up the effect of shade it might be stated tersely: it lowers the air and soil temperatures and breaks the action of the wind; these factors increase the humidity of the air and this increased humidity results in less evaporation from the soil and less transpiration from the plant; the final con- sequence is a greater soil moisture content with its correspond- ingly good effect upon the growth of the plant. Germination of Forest Trees 9 The effect of light upon the height growth of forest trees has been used as a basis for determining the relative tolerance of these trees. As early as 1866 Kraft (2) planted a number of different species in the shade of older trees and measured their heights and diameters several years later. Upon this basis Kraft arranged the species according to their tolerance. Nikolsky (2) in 1881 carried on similar experiments with pine and spruce and showed that the greatest length of stem was found in the trees which grew in the shade; the length of the entire plant above ground increased with increase in shade; the length of the main root as well as the number and total length of the lateral roots, however, diminished with increase in shade, while the total length of all roots of plants which grew in great light intensity was greater than the total length of all the roots in the shaded rows. At the Swiss experiment station in 1893 Badoux (2) carried on experi- ments on eleven tree species with different degrees of shading to determine their behavior in different light intensities and thus determine their tolerance. Fir and spruce had almost the same average height growth at different degrees of shading. With pines, larch, beech, and ash the growth on the contrary decreased in proportion to the shading. In the case of basswood, blue beech, and elm the growth in height was but little affected. The work of Wiesner (2) from 1905 to 1909, in various parts of the world, and of Clements and Pearson in the United States (2) between 1907 and 1909 was only for the purpose of determining the minimum light requirements of species as a basis for scales of tolerance. The last two investigators took numerous readings in the Rocky Mountains and noted the condition of seedlings under various light intensities. Burns (9) experimenting with white pine under lath shade in the nursery found that shading delayed the time of germination but that the final germination per cent. was about the same in both cases. He likewise raised white pine seedlings in full shade, half shade, and no shade and (at an age which he does not state) measured the length of the hypocotyls, tap roots and lateral root branches. He found the greatest length of hypocotyl in the plants that had been grown in the full shade, the greatest length 10 Richard H. Boerker of tap root in plants that had been grown in no shade and the greatest length of lateral roots and total root system in the no- shade plants. This bears out Nikolsky’s experiments along the same line. An interesting conclusion reached by Burns is that shade reduces the temperature of the soil and delays the time of germination. The work of Atterberg (9) which is quoted by Burns is given here for completeness. Atterberg studied the relation of light and temperature to the germination of pine seedlings. He found that at a constant temperature of 23° C. 80 per cent. of the seed germinated in the absence of light and 87 per cent. in the presence of light during practically identical germination periods. Burns concludes from this: “ Apparently a high and changing tempera- ture, light, and a moist seedbed are essential to satisfactory germination.” The investigations of Haak (5) and Pittauer (6) have very little bearing upon the problem at hand. The former at the mycological laboratory at Eberswalde studied the influence of season, moisture, temperature, light days and dull, artificial and natural light, color of light, intensity and duration of light, and the influence of chemicals upon the germination of Scotch pine seeds. He found that in lower temperatures germination begins considerably later and proceeds much more slowly that in higher temperatures, but that the final germination per cents. are about the same in either case. He found that certain rays of light were beneficial and certain harmful to germination. Pittauer studied the effect of different degrees of light and extreme temperatures upon the germination of tree seeds of certain European species, viz.: beech, black locust, and various conifers. He found that germination proceeds more rapidly in light than in shade and is most satisfactorily accelerated in diffused light. Undoubtedly considerable work has been done in the United States by the various forest experiment stations of the Forest Service but these results have not been, as far as my knowledge goes, published. In a very recent article in Science, Graves (7) speaks of such work being carried on at the Wind River Forest Experiment Station in Oregon. A recent discovery at this sta- Germination of Forest Trees II tion showed that the seed of Pinus monticola of Idaho lies in the duff and litter beneath the mature stands for years and then germinates when the ground is exposed to direct lighting. This is mentioned here, merely as another instance of the many of record in which it is assumed that light is to a large degree re- sponsible for the germination of certain tree seeds. Practically the only work of any importance on record concern- ing the effect of soil moisture and soil texture upon the early development of forest trees is that of Tolsky (8). He studied the relative effect of sandy and black soils upon the structure of the root system of Scotch pine. He found on black soils that pine developed principally vertical roots while on sandy soils superficial roots predominate. In rich soils roots are guided in their development by moisture, while in poor soils like sand, activity is directed mainly towards extracting nutrition from the soil. In poor soils nutrition is spread over a large area and in order to get it in sufficient quantities trees need numerous roots. Whatever the cause might be, Tolsky found more lateral roots and more superficial roots in the case of trees grown in sand, and this may be taken as the most significant part of his work. Before discussing the present investigations, I feel that it would be profitable to briefly summarize the edaphic factors of the habitat with special reference to the physical properties of the soil which play a physiological réle in the germination of the seed, Classification and Résumé of Habitat Factors The complex of climatic, edaphic, and biotic factors which influences the life, growth, and reproduction of a plant is known as its habitat. The study and investigation of habitats as entities avails us very little unless we analyze a habitat into its component parts and investigate each of these parts by itself. Clements (1) classifies habitat factors into physical and biotic. The former have to do in general with inanimate objects and the latter with human beings and animals. He further divides phys- ical factors into climatic and edaphic. Climatic factors are atmos- pheric in their nature and the edaphic factors are concerned with 12 Richard FH. Boerker the soil. He further subdivides climatic factors into humidity, light, temperature, wind, pressure and precipitation. The edaphic factors are subdivided in a similar way into water content, soil composition, soil temperature, altitude, slope, exposure, and surface, In glancing over this classification it becomes at once obvious that all of these factors cannot affect the plant directly. Many of those enumerated are in themselves very complex in their nature. For example, slope, aspect, altitude, and surface could each be subdivided into component factors, but if this is done it will be seen that they resolve themselves into those factors men- tioned above which are not divisible. In other words there are about three master factors which are able to affect plant life directly, and all others are combinations of these. There is no better way to bring out this idea than to give Clements’ (1) classification based upon the influence which each of these factors may exert on plant life. He classifies factors into those that have a direct bearing upon plant life, those that have an indirect bear- ing, and those that have a remote bearing. Direct factors are only those which produce qualitative structural changes in the plant itself. Furthermore, the classification of habitat forms and plant formations is based upon them, which fact merely em- phasizes that they are fundamental. Indirect factors are those that affect a formative function of the plant through another factor; and remote factors are those which are physiographic or biotic in nature and must operate through at least two other factors in order to produce a structural change in the plant. This classification is as follows: Direct Factors Indirect Factors Remote Factors Water content Temperature Altitude Humidity Wind Slope Light Pressure Exposure Precipitation Surface Soil composition Soil temperature Germination of Forest Trees 13 The germination of seeds depends principally upon edaphic factors, hence climatic factors will receive little attention here except in so far as they condition the former. It is taken for granted that the morphological and the physiological significance of water, light and heat to plant life are too well known to require discussion here, especially since that phase of botany is funda- mental in all ecological work. The water content of the soil is by all odds the most important edaphic factor in determining germination, for while other factors may condition this process to a certain extent, none but water, within certain limits, can prevent it altogether. In a synoptical manner I will briefly call to mind the significance of this master factor in germination and then briefly inquire into the important soil factors and properties that bear directly on the investigations at hand. The amount of water in the soil has no direct relation to the amount of water which plants can use. At the outset distinction must be made between the different kinds of water in the soil and which of these are available to plant roots. Usually three kinds of water are distinguished, namely: hygroscopic water, capillary water and free water. Hygroscopic water is that water which plants cannot get owing to the enormous film pressure which holds it. It is also known as the amount of water in an air-dry soil. Capillary water is that water, most of which is available to plants and is held against gravity around the soil particles by capillary forces. Free water is that which is not held either as hygroscopic or as capillary water. It is water influenced in its movements by gravity and is therefore called gravitational or hydrostatic water. Clements (1) calls these echard, chresard, and holard respectively. It will be seen then, that the only water available to plants is a part of the capillary water which surrounds every soil particle and fills every small pore space. The principal factors which influence the amount of soil mois- ture available (capillary water) to plants are: t. The amount of water reaching the soil. 2. The catchment of water by the soil. 3. The water-holding capacity of the soil. 14 Richard H. Bocerker 4. The amount of evaporation from the soil. 5. The amount of water withdrawn by other plants. 6, ‘Vhe replacement of loss by capillary movement. 7. The amount lost by seepage, percolation, etc. Of these factors, only four are important in the present investiga- tions. These are the water-holding capacity of the soil, the evaporation from the soil, the replacement of loss by capillary movement, and the amount lost by seepage and percolation. The water-holding capacity of a soil is determined by soil depth, soil texture, and the amount of organic matter present. In soil tex- ture two factors are important, namely, the size of the soil particles, which affects the surface area of the particles and the amount of pore space in the soil, and the density of arrangement of these particles. It is largely for these reasons that loam will hold more capillary water and will contain more air space than sand or gravel. Evaporation from the soil naturally affects greatly the amount of water available to the plant. This is affected by climatic factors such as temperature, relative humidity, and wind; and by soil factors such as texture, color, depth and the character of the surface. The replacement of the loss of soil water by capillarity depends upon the rise of water from the water table. This rise is conditioned by the degree of saturation of the lower soil layers, the texture of the soil, the height to which the water must be raised and the character of the intervening soil layers. A fine-textured soil like loam or clay is much more favor- able in this respect than a coarse-grained soil like sand or gravel, principally on account of its great ability to obtain water from the lower soil layers. The amount of water lost by seepage and per- colation depends largely upon the texture of the soil. The coarser the soil the greater is the amount of water that percolates through it and the less is the amount held by capillary forces. As far as it determines the amount of soil moisture available to plants, soil texture is certainly the most important physical property of the soil and it deserves a foremost consideration in all problems that pertain to the germination of seeds. Germination of Forest Trees 15 The Gernunation Process (10, II, 12, 13) This period in the life history of the green plant is unique in that the organism is independent of an external food supply and also of all luminous energy. Germination may be called a period of growth without photosynthetic activity, and it terminates at the time the accumulated food in the endosperm is more or less ex- hausted. During all this time it is without light; it does not require it, but lives in total darkness beneath the surface of the soil. While the seed has no use for light, it does require water, oxygen, and a certain amount of heat in order to germinate suc- cessfully. The dependent life of the plant begins at the termina- tion of the process of germination, when the first ray of light strikes the spreading cotyledons. Light sets the photosynthetic mechanism in motion and this marks the beginning of the plant’s manufacture of food; henceforth it is dependent upon its en- vironment. _ The rdle of water in the germination process is to aid in the > transformation of the accumulated nutrient material into food that can be used by the germinating embryo. In other words, this factor is instrumental in taking this sunken capital and trans- forming it into specie for circulation. But water cannot do this directly ; it must act through the agency of certain catylists or enzymes. These enzymes transform insoluble and indiffusible foods into soluble and diffusible ones which in turn move from the endosperm to nourish the embryo. Water is important to the seed for two reasons; its absence determines the seed’s power to live in a dormant condition, whic is one of its most important properties. If a seed is not dry i cannot be preserved ; we cannot secure good seed in a wet autumn. The second reason why water is important is because of its chemical and mechanical action in germination. Hales at the beginning of the eighteenth century showed that the absorption water by seeds is generally accompanied by a considerable mani- festation of energy, which takes the form of swelling. Chemically water acts as a solvent for the enzymes which render the ac- cumulated foods soluble. 16 Richard I. Boerkcr Practically all the accumulated foods in the endosperm must be transformed by the action of enzymes, which in turn must first be dissolved by water. Starch, which is insoluble in water, is converted by means of the enzyme diastase into a soluble sugar. Throughout germination the quantity of starch in the seed de- creases; the starch grains at first corrode and finally dissolve completely. Many albuminoids (simple proteins) are likewise insoluble in water and certain soluble albumens cannot diffuse through membranes. A pepsin-like enzyme which develops dur- ing germination acts upon the albuminoids, transforming them into soluble and diffusible forms. Others are changed to crystal- loids which after solution diffuse very readily. Fats and oils are likewise insoluble. Certain enzymes during germination decom- pose oil into its constituents, fatty acids and glycerin, the latter easily soluble in water. It is well known that fatty acids when set free assist the breaking up of oil in water into very fine drops with the formation of an emulsion. Heat is important in the germination of the seed in that it may accelerate, retard, or even entirely stagnate the processes begun by the action of water. It might well be said that the rapidity of germination depends to a large extent upon heat, since it has the power to modify the action of enzymes. Temperature likewise affects the diffusion of liquids. A considerable part of the heat used in germination is generated by respiration. This process sometimes raises the temperature of the seed as much as 40-50° F. above the surrounding temperature. Certain seeds owe their ability to germinate at very low temperatures (below freezing) to the heat generated during respiration. Certain arctic and alpine plants are able to blossom in the snow for this same reason. Seeds in water, seeds buried too deep, or seeds surrounded by air deprived of oxygen do not germinate even if other conditions are favorable. In other words, water and heat are of little avail without oxygen. Even before water and heat can act through the agency of the enzymes, in many cases another factor must come into play to release the enzymes. The latest investigations show that the formation of diastase is intimately connected with respiration. In a similar manner respiration supplies the energy Germination of Forest Trees rz which oxidizes the fats and oils of the endosperm. It has been noted that the quantity of oxygen absorbed is much greater in the case of fatty seeds, like those of the pines and birches, than in the case of the starchy ones, It has been known for a long time that seeds lose weight during the process of germination although no solid matter is lost as near as can be determined. lf we take a certain quantity of seeds and weigh them both before and after germination, being sure to get the dry weight both times, we find that although the seeds have increased in size, they have lost weight. This is due to the loss of certain elements like carbon and hydrogen. In the process of respiration the carbohydrates in the endosperm are broken down, carbon and hydrogen are lost while the quantity of nitrogen remains practically constant. In the process of respiration, the products of combustion are carbon dioxide and water. —— Respiration in the seed is quite different from that in the case of leaves and other green parts of the plant. Seeds are generally not provided with intercellular air spaces, but oxygen penetrates to their interior chiefly by diffusion from cell to cell. Thus it will be seen that the supply of oxygen to the deep-seated cells of the seed is most liable to become insufficient. This of course retards germination. If the supply of oxygen is reduced materially, due to lack of soil aeration, germination may be prevented. The best aerated soils are those that have comparatively large interstitial spaces, like sands and gravels, and the poorest ventilated soils are the heavy loams and clays which are small grained and compact and have minute interstitial spaces. The seeds of different tree species naturally vary as to their soil requirements in this respect. This explains why tree species of sandy habitats germinate so poorly on clay soils. From what has been said, it will be seen that water, heat, and oxygen are the essentials for germination, and that the lack of any of these factors is sufficient to retard, if not entirely to inhibit the process, It is a well-known fact that seeds have a power of remaining dormant for a period without affecting their vitality. The power to retain this vitality is due largely to the nature of the seed-coat' 18 Richard H. Boerker which insulates the embryo from heat, water and air and protects it from mechanical injury. Cottonwoods, willows, elms, soft maples, and white oaks have a very short period of rest. Usually the period is not over six months, but basswood and hornbeam lay over from fifteen to eighteen months. It has likewise been noted that some tree seeds must lay over for a certain period before germination can take place. The common experience of attempting to germinate seeds in mid-winter which have been gathered during the previous fall is proof of this phenomenon. This leads me to a brief discussion of the process of after-ripening as it is called. Many seeds we know require a long‘time for germination in spite of the fact that they are surrounded by the proper condi- tions. During this period it has been found that certain chemical and physical changes take place which are necessary before the seed can germinate. The length of delay is apparently de- termined by the persistence of the structure of the seed-coat and to the conditions under which the seed is exposed. The term “after-ripening ” has come into use to designate the changes in the seed during this period. Eckerson (17) concludes that most cases of delayed germination are due to the exclusion of water or oxygen by the seed coats. But some seeds do not germinate after all coats have been removed and the seed put into germinating conditions, indicating that the delay is due to embryo conditions. , It is now certain that some changes within the embryo are necessary for germination. In the case of Crataegus used by Eckerson it was found that food is stored in the embryo in the form of fatty oils; neither starch nor sugar is present. A series of metabolic processes takes place in the embryo during the period of after-ripening. At first there is increased ‘acidity accompanied by increased waterholding capacity. There follows an increased activity and production of enzymes and as a result the fats decrease and sugars appear. The appearance of sugars which are soluble and diffusible marks the beginning of the germi- nation of the seed. All recent investigations both in America and abroad show how extremely complex is the role of oxygen in germination. A set Germination of Forest Trees 19 of conclusions based upon one species of plant apparently may or may not hold for others. Shull’s investigations (14, 15, 18) are based mostly on Nanthiuim seeds. In his experiments he finds no evidences of the diffusion of oxygen through an absolutely dry seed coat. This is significant in that it shows an important role of water in preceding oxygen in penetrating seed coats. Ex- perimenting with Crataegus mollis Davis and Rose (16) find that seeds treated dry or those placed under water do not go through the process of after-ripening. Here again is evidence that both water and oxygen are necessary. These investigators, working on the effects of temperature upon the period of after-ripening, conclude that favorable moisture conditions and temperature con- ditions shorten the period. Atwood (19) confirms almost all of the conclusions drawn by Eckerson although working on Avena fatua. Crocker and Davis (20, 21) worked with water plants and their results totally different than those described for land plants need not be given. Unfortunately these conclusions are not based upon forest tree seeds. Such investigations have not been undertaken. This phenomenon will probably explain many of the cases of delayed germination which are well known to foresters. It is reasonable to assume that the conclusions based on Crataegus would also hold for such fatty seeds like the birches, spruces, hard maples, etc. It is also reasonable to suppose that most tree seeds pass through this period of after-ripening during the winter months ; if this is true it explains why it is often impossible to germinate certain tree seeds immediately after they have been gathered. Method of Attacking the Problem There are two general methods of determining the causes in- fluencing the behavior of seeds or plants growing under natural conditions. These are the observational and experimental methods. In the observational method we observe the kind of vegetation produced in response to a certain complex of physical factors and seek to find constant relations of one to the other in order to draw conclusions. In the experimental method we may 20 Richard H. Boerker either synthetize an artificial environment and proceed to study the plant under definitely measured differences of light and water, or we may measure the physical factors influencing the same plant under various natural conditions. The observational method is ill suited for most work on habitat relations because the habitat involves an extremely variable array of uncontrolled physical factors, and it is practically impossible to determine without actual measurements which factor has the controlling influence and what the relative importance of the others are. The most desirable method for problems which will allow its application is the one in which we synthetize an artificial environment. In this case we keep certain factors constant and measure the variable one; in this way, it is quite obvious, the environment is comparatively easy to analyze. This method, of course, presupposes a greenhouse and on this account is only of limited application. There is no question that all these methods have their value in their proper places ; the choice of one must vary with the problem and the circumstances. The method of measuring the factors influencing the same plant under various natural complexes is the one probably of widest application in the field. The purely ob- servational method, for work on the determination of habitat factors, while of some value when other methods are impossible of application has tnsurmountable objections. Observers in vari- ous parts have no common basis or standard; their mentai equip- ment and fund of ecological knowledge vary greatly and they may even have very different points of view. Some of these ob- jections might be summed up in the term “ personal equation.” Another danger in this method is that of applving local observa- tions to large areas, in other words, in generalizing on the basis of too meager observations. The conclusions drawn in the ob- servational method are largely in the nature of opinions modified as indicated above by the personal equation, while the experi- mental method produces conclusions based upon actual figures which are indisputable and carry the weight of scientifically proven facts. Another objection to the observational method in determining the effect of habitat factors is that this method studies the effect Germination of Forest Trees 21 and not the cause of the factors. It is a most significant fact that the same habitat factors do not always produce the same effects upon vegetation even under apparently the same set of conditions. The effect of two habitat factors or groups of factors may be the same so far as the structure and behavior of the plant is con- cerned, yet upon inquiry into the causes concerned we might find in one case it was due to temperature and in the other to soil moisture. In a similar manner it is known that other factors besides light determine tolerance. In other words the study of the effect of habitat factors upon plants does not always lead us to safe assumptions as to what the underlying cause is. The only safe method in this kind of work is to measure the cause, thus employing a direct method instead of an indirect one. Methods and Apparatus Used in These Investigations The investigations herein described were carried on in the middle room of the west greenhouse of the botany department of the University of Nebraska. For the germination studies three series of cultures were used, namely, the light, soil-moisture, and soil-texture series. For the experiments and measurements in connection with the early development of roots and stem a fourth series was added, namely, the soil-depth series. In each series three degrees were used. In the light series open light, medium shade, and dense shade were used; in the soil-depth series shallow, medium deep, and very deep soil was used; in the soil-moisture- content series, dry soil, medium wet soil, and wet soil was em- ployed; and in the soil-texture series loam, sand, and gravel were used. The values of each degree in each case will be given later. As the experiments progressed it was found that the amount of greenhouse space assigned to the work was not sufficient, so that the open light culture, the wet soil culture, and the loam cul- ture were combined into one since these were being run under identical conditions. (For arrangement of cultures see page 33.) The seeds for these experiments were obtained from any source it was possible to get them. Large orders were sent to almost all large commercial seed houses at one time or another. On the whole the response from these orders was very discouraging. At 22 Richard IT. Boerker the time the seed was wanted (early fall) many of the seed crops had not been collected. Likewise it took time to determine whether there would be any crops at all in the case of some species. This resulted in delay in getting the work started. By the middle of January eighteen species had been obtained from commercial seedmen and of these only seven produced results that were in any way satisfactory. On the other hand, through the kindness of various members of the Forest Service throughout the United States, twenty-six species were secured and practically all of these produced good results. Due to these facts anyone undertaking experiments of this kind in the future must look a long ways ahead for a good seed supply. The following series of tables gives the source of the seed obtained together with what information was available as to date and place of collection. The nomenclature used here and throughout this report is that used by the Forest Service and is according to Forest Service Bulletin No. 17 by G. B. Sudworth. Species SUPPLIED BY THE UNITED STATES Forest SERVICE Species Piace Collected Date Pinus ponderosa ......... California. scsssscesxcsawecusienerzawts ? Pinus ponderosa ......... Pecos N. F., New Mexico ............. 1913 Pinus ponderosa ......... Weiser NuOCE.,, IGANG: cccsoccscia sie. cciceceoneneieraia 1912 Pinus ponderosa ......... Harney N. F., South Dakota ........... Igi2 Pinus ponderosa .......+. Bitterroot N. F., Montana ............. 1912 Pseudotsuga taxifolia ..... Pecos N. F., New Mexico ............. 1913 Pseudotsuga taxifola .....Caribou N. F., Idaho .................. 1912 Pseudotsuga taxifolia ..... Madison N. F., Montana ............... IQII Pseudotsuga taxifolia .....\Western Washington and Oregon ...... IQII PRUE TOPPED cvcretseiieu ea dent WN. Ae, CalitOnniay wasccccnoes vec sanise 1912 Abies CONCOLOP sisisccieaeeds Durango: .N. F., Colorado ws: sseaxcse ss 1913 Tsuga heterophylla ....... Olympic N. F., Washington ............ IQII Pinus lambertiana ........ Teasseni JNs Fs: (Califo ena oe ots: o : casssacacicess 1910 Libocedrus decurrens ..... Eldorado N. F., California ............, 1914 Pinus palustris cacsevecvss Florida N.. F-,. Florida: .....ccccccsicy siaws ? Pinus coultert .....0cccces Monterey N. F., California ............. I91o Abies magnifica ........... Sequoia N. F., California .............. ty Sequoia washingtoniana ..Sequoia N. F., California ............., IQI2 Pinus divaricata .......... Minnesota N. F., Minnesota ............ 1910 Pinus contorta ........... Arapaho N. F., Colorado .............. ? Pinus resinosad ..........- Minnesota N. F., Minnesota ............ IQIO Germination of Forest Trees 28 Larix occidentalis ......... Colville N. F., Washington ............. IQII Abies lasiocarpa .......... PHest Rivet, dah! auiewisensonsecesse, taurine 1913 Abies grandis ..........05. Priést Raver, FdahO? siicsmewcsvnceasnsaxa-s 1913 PrCOG: SURCNSIS secccouorea de Coast of Washington: ccxnirnracaaeceren IQII Pinus monticola ........46 Priest River. Idaho: xcscsscusesans caaxes 1914 Species SUPPLIED BY COMMERCIAL SEEDMEN OR COLLECTED Species Place Collected Date Puts. SHOOUS: a.cocncdan ves Carta as-is. caishcis ss oars g aswihuaed meaner as ohn 1913 Ean? CUPOPER? sxcscgsrereewees FETROPE! ecnsns sideman nati h Oana 2 Pinus ponderosa ......... Black: Hulls. “South Dakota. ccncicacea seca 1913 Pinus divaricata a.2.00.0% Northern. Minnesota, so xscasnseushencrens IQI4 Robinia pseudacacia ...... EUROPE: aciiaacumeennes oh044 Seon ? Catalpa speciosa ..... ese NDIA i-th acon cxtemrid.a arctcsnuntueusaatess cece nS 1913 Quercus rubra .oce ce ccees MCR ISAS <5 dydescsons, ida. Se arutonin de waemoteetues 1914 Acer saccharum .......... ITT OLS vacivestunededucattodubcgenaraeusadauerienaaets’e 1914 Liriodendron tulipifera ..,.OhIO wo... ccc cece cece eens IQI4 Betula papyrifera ......... Perris vatwar joie cuseccmtvaletemaneeetfalcters 1914 Abies balsamea ........... Maine: saneuensieeiaset a eae ae 1914 Pseadotsuga taxifolia +:<4 Golorad©: scacascceiyy sour eeeeneeeantees 1913 PUR G TOCA OE icchsusatssndctuets ose OUCH LM States) 0-5 5.2 ro.3 26.5 TO 2O io cote sand 6 datuingns 0-9 4.3 9.4 2755 DD. acs 5s Sand aobntnaceads 0-9 6.8 11.8 4-9 DMs GiGaih doe seated 0-5 5.7 15.7 40.0 TG TO vat 3 forcast tate, oman a5 5.1 ; I25 36.6 6/25 ios “ratios eran eens 0-5 3.0 : 6.3 17.9 Te) 3 Ole iaieg = 6k gia. aac 0-5 38 wor 18.8 2)Oh.n ae ened en eomaunes 0-9 4.7 12.4 20.7 DIT Becigh ss Se we ee hckeas | 0-5 4.3 Pere 19.0 BI20% tose 2458 S44 sees 0-5 6.3 13.8 23.3 127 eerie ct ta sae Same 0-5 5.4 14.1 483 BOM iestusisna d.cotuaupdionsenetos 0-5 4.0 9.4 29.9 BAUS his whegianwteamapen se chess 0-5 3. 6.7 19.8 SY 20M cise ci dhe ertoa et de sa eves 0-5 9:5) 9-3 19.6 BU LF sa tates a8 wcewanctahne. Grae 0-5 4.5 | I5. 20.9 AB cc tapletey.e ae oc ania gee 0-5 4.5 | 12.4 19.8 AITO | go. | zor Pinus ponderosad.......... Idaho | 90 & | s.0 a4 | 92 lorax 36 | so |.ao.0 Abies grandis.......2054. Idaho | — | —} — 66] 10; 3 0) 36 | 36 | 4.0 Abies lasi0cerPGs cesencnas Td@ahe.| a> | es — 84 Y | We) 30 | 30") 6.0 Pinus MONUCOlGsascnaanee Idaho | 48 I og 18 | 38 | on 2H [ So | B25 As in the preceding table, Table V shows that the beginning of germination is delayed in most cases and that the germination period is considerably shortened with the decrease of soil moisture content. Only 1 species, Pinus ponderosa (N. M.) showed a higher germination per cent. in the medium wet soil than in the wet soil, all other species show a higher per cent. in the wet soil. 40 Richard H. Boerkcr Tue Errect or Soil Aloisture UPON GERMINATION tt 4 rt : t t + + Tt ze Ht t f i ce t . a pa Ht t } r : r + t crt t = t ¢ eaeene - acsuuwes sat is f ab peaaeas t | Ht : Se t ay roe cepa t t +f f ¥ He t He : T t feet TH i i seeat : z r t 1 t it f t f ott i ; t Sorte thet anes sueeses sensnesss i peace eas i r ae = lade tase oa inandecs t Seer Ht 3s cssosseas sae t { t f Fic. 1. The germination curves of Pinus ponderosa (S. D.). + t ; + ned suunasaues senses t i feet eeeese : t sEseneest weet w +] = pana r aaeauaes peanaeel tt tf L ; He + Het HA jsnaaas Ho Ht t t aa TH it 7 + Ht rot rt va POL ERY 15 Cort t t 1 ia t t t t t t t t t ri [ t t 7 ‘ t i + t H : pabie Patents LG Fic.2. The germination curves of Pseudotsuga taxifolia (Colo.) Gerinination of Forest Trees 47 It is evident from this table that the two most drought endur- ing species are Pinus ponderosa (S. D.) and Pinus ponderosa (N. M.). While other species germinated in the dry soil their germination per cents. were very small. Among the intermediate species, as far as soil moisture goes, are Abies concolor, grandis, and lasiocarpa, Pinus contorta, Pinus ponderosa (XMon.), and Pseudotsuga tavifolia (Mon.). It is interesting to see that with one exception the only species that germinated in the dry culture were either Pinus ponderosa or Pseudotsuga taxifolia. The former from the Black hills, New Mexico, and Southern Idaho and the latter from New Mexico, Colorado, and Idaho. The line is evidently drawn between Southern Idaho and Montana as to whether these species will germinate in the dry culture or not, since both species from Montana did not germinate in the dry culture. Another interesting fact is that there are no moisture- loving species in the Rocky Mountains so far as this classification and these species are concerned, since there are no species that germinated only in the wet soil. On page 46 are given the curves of Pinus ponderosa and Pseudotsuga taxifolia in their relation to soil moisture. These curves show that germination is delayed, the curve rises less rapidly, the period is shorter, and the final per cent. lower with a decrease in soil moisture. TABLE VI Tue Errecr or Soil Moisture oN GERMINATION Pacific Coast Species LLORES occ sre ie RA CRAM | EBGPU8 OCCIMENL AUIS sii sercnca ioe an nied oxen —|-— PSCHDOTUBE TAB ON cg opi gaw renee —|— — 22 | 28 | 6.0 Dry Soil Medium Wet Soil Wet Soil Species culty 8 dul va = calcu ag BO [LA BB) me | aA es aR) SA es Pinus ponderosa (Calif.)........-. _—|—|— | 68 | 12 | 6.0) 42 | 67 | 61.0 PUARS JOTI sa ecagun RAGE REA DRS —{|—!]-— | 80 6 | 12.0] 31 | 77 | 22.0 Pinus lamberizenve So RTL UnAQnds 429 VY 8 gI vs oz gI bz or vz I 89 vr VI vz QI gl Dei] oS PP Le B reisieeas DSOUISAA SNULT gr gr gI 91 oc TI gi ta4 ZI gz bz oI gz vI Oz VI CSA) DIDI1ADAIp Snulg ov or ge Zi ze ZI os vr vz ov ge ol 9z or ze Bde [re eet tas DIDIADALP SNULT y os) » sl i) w ‘W oo is) oo ‘ we i) ow g w va os eo os oo as eo oS oe os oA wo on os eo os e aan sayoadg feazig pues eae RA FETS wos Arq shase capa =n ee PINYX2T [10S BINISIOJA [IOS qWysrT SaINadS snojiygosaX AO NOILVNIWUAL) AHL NO a4nj Ha, [10S ANv ‘aanjsropy [0S GyhIT 40 Lada ABI, xX ATAVL 59 Germination of Forest Trees fib gic og fre [Orr | Loz jose iggh jaSt jroz [SSS | |e Ze TOW | LOE Ar ees TLE TER SaSBIsAV | =< — — Iv zs 8 | 06 z9 zs of vs Iv se a **2499]NOI SNUIT 98 oz 0g gz LL Ig] 9 og | vs 0z tg faa LL i 2 ‘+ akasfal snurg of of zB oz L9 zy ZI 89 ZO cz z6 ze 49 | dui ‘+ *(yyeO) psosapuog snurgq — —_ — _— of of I vg gz zz os gz of of fre DgADIOISD] S31QY 9f gf 9 ov 9£ 9f or 99 09 c% ZO ce 9f Qe s+? “sipuDds Sa1QV I gr gv gr ZI gr gs gi 8 or vs or ZI Be hee ee ree ‘+++ CUO) DSosapuog snutq ze | oct | be! zx | ve | vr} oz | gt | be] ez| c€} 2rj ve | br ft (uo) DHofexn2 DEnszopnasg ol QI 99 0% og VI 99 oz zl VI oL or 0g VI DIAOJUOI SNULT gt oz 99 gr os vz gz 0g 09 vI ps gr os vz *40]09U02 Sa1Qy ve gI e1 gI ay gI 9 zz vI VI oz vi eI she ica ll ( ate pso1ads Dg1DIDD ov 91 RE. vr of gi cz ze gf gi get gi of CM ah ae ae ae a “DOUDSIDG Sag Vy ae) cz vs gz es Ie os gf Fae) ze zg ee es 1é setts sstasnipdg snug ge | ve] ve gi os zz| ve | of | gz VI vs 91 os fad SNQOAIS SHULT td i] a) vs] yg mJ yg wo a) w a) w yy io be | be | 9s | Se | Pe | Se | Fe | Se | Ps) Fe | F3| ve | Fe | ge SE/ SB |S /SE | SR) 45) SR) ob | 32) 35 | oa | 35 | 32 | ah amnyng [0S AM apeys apegs aainyag sepeds PAM pues aS wMIpayy asue(y wnIpayy Pecitie) 94M}X9[, [10S aIMys}oy [!OS wysrT SUIAS snoprygosau-049X IO NOWLVNINUID INL NO anjxay [0S ANY ‘adnjsioyy [10S “Hy SY] 40 Lodday INL IX HIGVL 60 Richard H. Boerker so as to make it an ideal soil for germination. Hence we might expect to find the longest germination periods in the sand. The average figures show that this is the case in each group of species. The shortest periods in every case are either in the loam or the gravel because loam is unfavorable from one standpoint and gravel from another. In comparing the check cultures of the three groups of species it will be seen that xerophilous species germinate first, xero- mesophilous next, and mesophilous last. In other words the drier the habitat the sooner germination starts, granting that the conditions are favorable. TABLE XII Tue Errect or Light anp Soil Texture oN THE GERMINATION OF Mesophi- lous SPECIES Light Soil Texture Check Medium Dense Check Culture Shade Shade Culture Sand Gravel Species — “== -- | = ee ee an 3 a“ ae gal ge PRS FOOD se eben ee 9% 34.) 6 Catalpa speciosa (Ind.)....;/18 | 1 QueKCUS TUDT GE... foie Rees 40 |28 Betula papyrifera........ ea.) Er Pinus lamberfiana....... 70 ‘36 Abies magnifica.......... 44 |52 Sequoia washingtoniana...|16 |18 Tsuga heterophylla....... 66 | 1 PUCCh SURCHSIS sien se 4 x38 22 |60 Pseudotsuga taxifolia OWES) 5 etree ae erases 22 '28 \ { Ws eae hee Averages?............. 35-9 28.6/31.7 27.9130.0 30.1, 38.7 25.5|40.4 27::0)40.7-27:0 Tables similar to X, XI, and NII were constructed showing the effect of these habitat factors upon the germination per cent. of the species. This table is not given but the most significant facts which it shows are given here and in a later table. It is interesting to note that of the 37 species used in the experiments the highest 2 Catalpa speciosa and Tsuga heterophylla not included in averages of light cultures. Catalpa speciosa not included in soil-texture averages. Germination of Forest Trees 61 germination per cent. did not always occur under the influence of the same conditions. Considering all factors and all degrees of these factors the highest germination per cents. occurred as follows: DO POT LTE AB etae esc fetes tia ode arenes alee da eee 3 TInt sme dium, Shade: a sewsievacas vee seadwa scotia aves Pe essen a Dnt dense shade’ scacceswincein ics wacsiics a.ddstsnie sa lasaodacdieminvewieiaeess II Dt SEAT Per crsace ath cud yrtnsetsausvelesalpadiava esarateconvovovendnareens ie oaaailela 12 MEME tase astyeticcanacacesesnavars sl =} 3) =| NH seag iS) janeel i] & anna rt n Gu vo toto) v a u < iS) i ty : a eoeseues HaEeReee! + on 1 a EEE EEE HEH HH tt ae + +4 1 roy ttt :) +: H Hy H ts 4 a at 80 Richard H. Boerker Seedlings from Seeds Size, Cm. Small Large O05. nein nnceane acautealemvaccaue oe 2 o O.O2110) eiitemaasaa den ddiamabaarnteisces 10 o MST TaB aayncenee hice iste ascends 17 6 TODO). ns cPacercnann augvacnnanecayeens OR oyesers 26 14 MGS! WACK A ee nasiikem eee was 24 19 BIOL ON Adunvawalaenamhitanilemamcmedes 25 25 SPER) A tat eecrencesed cater cadattoeacn ea salons 30 26 SO-AO: Sexonsams teeneseosinnastunnes aie 23 31 BNrES. Gils taancs ee cuusiactiaiea dee 1S ig BOAGO™ aicesssccen in acrsacuecattianioneatemweg II 15 GubS5 iS: | auganenoinns caida maetunalatas 8 13 SOOO) - etaatemscu mena wane eet 4 12 Os AGiSt — ne acamare cniticwa dasa ates 3 9 DIORA FEO palsissaotexsecincrcsstosacaboui inside sda tanec’ is) 8 ALT AG). Hisar ehahasevesasav eh ico lees orgeesedengnans See te) 2 POH=SiO © talerrercrren saints Riera scusmeme es I 2 BIBS aniancsdssogdierwe veeeee I fa) OOO) dauts iesntevin ath ceaducuie aoanagitaasaodanehegehaea I I Motall..