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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) <a. ohinas decane caenaies e Taxodium distichum ...... SOUtHEt: GtAtES, cuss senewmacdieas wtenecoen ? Liquidamber styraciflua ... North Carolina ............00 0.0 e eae 1914 Acer saccharwm ...c0..05- Canad ae” pascecceniater mince euk aint Re teSa aye 1914 Acer cubvrum soxcscacusens New Hampshire: scacesce sc gawddounesys 1914 Fraxinus americana ...... Indiatias cmincnwesas aa cesree bees teas 1914 Juniperis virginiana ...... Missouri River, Nebraska ............. IQI4 Gleditschia triacanthos .... Lincoln, Nebraska ..................+4- IQIS5 Pinus monticola ........ «/Gladier Park, Montattay s.c4.0.genescdinests 1914 Catalpa speciosa .......... Lintela, Nebtaska. cansccicecdatacsacrnps IQI5
In the body of this report, in order to distinguish the climatic varieties of a species, the name of the state in which the seed was collected is given with the name of the species.
The first planting was done on October 28, 1914. From that
time on plantings were made as the seed arrived. The last seeds were planted March 21, 1915. All experiments were conducted between the first date mentioned and May 1, 1915, a period of 184 days. In all cases ample time was allowed for the completion of the process of germination. This time naturally varied with the species. For most species three months was allowed but in the
24 Richard H. Boerker
case of certain Pacific coast species four months was apparently necessary. Three months ordinarily is plenty time enough ; usually if a seed in the forest fails to germinate in that time, it usually does not germinate at all, especially in the west where the dry period sets in after the spring is over.
Ten of the species mentioned in the foregoing tables failed to germinate. These species were Larix europea, Acer saccharum (both), Liriodendron tulipifera, Taxodiuim distichum, Liqui- damber styraciflua, Fraxinus americana, all of which were supplied by commercial seedmen. If the data regarding the collection of these seeds is bona-fide, their failure to germinate must be ex- plained by the fact that they had not completed their resting period. In the case of Juniperis virginiana, Gleditschia tria- canthos, and Pinus monticola, whose place and date of collection is known absolutely there can be very little doubt as to why they failed to germinate.
The soil used in all cultures (except the sand and gravel) was a garden loam of excellent quality with a mixture of about 25 per cent. of white sand. The mixture was prepared in the green- house. This made a very good soil for experimentation purposes. The sand used was common white, quartz sand with but a very small per cent. of hornblende and magnetite. The gravel was the kind used by the large construction companies around Lincoln for concrete work. Mechanical analyses of representative samples of these soils are given elsewhere.
All seeds were planted in rows at a depth which was 2'4 times the shortest diameter of the seed as near as this was determinable by the unaided eye. The rows averaged 3 inches apart and about 24 inches in length. In general 200 seeds were used of each species when the seeds were of medium size or smaller; for some of the western pines only 100 were used because of their large size.
The Control of Habitat Factors
As has been pointed out, the only safe way to study the effect of the factors of the habitat upon the life of the plant is to measure one variable factor while all the rest are kept constant.
I
Germination of Forest Trees 25
This principle is fundamental in mathematics; a single algebraic equation with two unknown quantities cannot be solved. In each of the series used in these investigations it was the intention to have only one variable habitat factor. In this way the study of cause and effect was much more clearly brought out,
The soil moisture determinations were made for four different purposes :
1. Asa check upon daily watering in similar cultures,
2. To show the effect of shading on soil moisture content.
3. To show the minimum content in the soil moisture series. 4. To compare soil moisture content in loam, sand, and gravel.
The samples were taken in certain cultures and at intervals varying with the purpose. The samples for the moisture content series of cultures were taken once a week, all others once a month. Each sample consisted of from 50-100 grams of soil, and was taken at depths varying with the development of the plants in the culture. In order to provide against error each sample consisted of from two to five portions taken from spots several decimeters apart, care being exercised that no soil was dug near holes where previous samples had recently been obtained. The samples were always dug between the rows of seedlings. The samples were immediately weighed and dried at a temperature of 95-105” Centigrade to constant weight (24 hours). The per cent. of water was computed upon the dry weight of the soil.
All-the cultures except the dry soil and the medium wet soil cultures were watered every evening. As was noted above, when the amount of room for the germination tests became insufficient the number of cultures was reduced from 12 to Io by eliminating two duplicate cultures. The only check moisture samples which will be considéred here are those that have to do with the three cultures which were being operated under identical conditions. Samples taken and recorded hereafter will take care of the other cultures and series. During the time (three months) that these duplicate cultures were run, one set of soil samples was taken as a check to determine whether they were being watered equally. These figures follow:
20 Nichard Tl, Boor ker
Crimes Sou. Moisruik SAMPLERS tpt Depth sa cm.
Name ol Cult Moisture Der Cent,
Cpe He fasas caadeeaecen Rae. Sasa ees ee ZN Wet. soil cxguccias see aciteaieeh Enid kienen Mamma RS eel VOU: ep puataeeteat oe ycesuneen gh piace Hap OG 4 wig fraumavenaieed DE TT een sel: seen ess Lo eGR RMR HE ROT REN CERERMGTE See Medium depth 2.00.00. ccc u LGU L as Lae age Gabnerieln LEG Shallow sth socce caciaes pM AT PEATE RANG 6 MR Ole
These figures, obtained after more than two weeks of datly water ing, pretly well indicate the small amouut of variition in moisture content which results in a number of cultures under the same conditions,
Light was controlled in the greenhouse by means of shade tents, Vhe cast bench of the room was divided tito three parts and the portions at the ends of the bench were covered with cheese cloth. “The central compartinent of the three was not ised on account of the shading influcnee of the tent to the south of it. (See page 33.) The tent intended to develop meditm: shade was made of a medinm grade of cheese cloth, while the tent titended for the dense shade was constructed of a double layer of heavy cheese cloth. ‘The light values developed in these tents and in the full light of the precnhon-.e as determined by a Clements photon: eter are viven below:
Tante or Liang VALUES
ith ap ias Open Moclitiny Petes Sumber ‘, nuke Hn Vighe Shade Shade We vlinggn Weather zi : nn eo ane ae Perens 11/21/14 | Tryo A.) 0.4250 | 0.1775 | 1... 5 Clear 11/27/14 | 12:00 A. | o.qo4o 1407 OO2LTO 4 Clear ————--- a ee aeenenee AVOLABC i beau cheos O.4IAS | OG2t 0.0216 | ora
These values are based upon full sunlight just outside of the greenhouse, These tables indicate that: full greenhouse lipht is approximately ¥% of full daylight and that the medium and dense shade tents have values approximately Y and Vyof full daylight respectively,
Germination of Forest Trees 27
It is quite natural to wonder how these values compare with values that have been obtained in the woods. Probably the com- parison of the light values obtained in the dense shade with some of the lowest values obtained in the woods would be most interest- ing. Clements (2) found light values from 0.12 to 0.05 under mature lodgepole pine in Colorado. He observed that Douglas fir occurred very rarely in densities below 0.05. Wiesner found the same value in this case. Pearson in Arizona found that western yellow pine seedlings grow fairly well in a light intensity from 0.309 to 0.414. White fir was found in good condition in light intensities of from 0.027 to 0.068 and healthy young growth of Engelmann spruce was found in intensities of from 0.033 to 0.062. In Oregon Pearson found such tolerant species as alpine fir, Engelmann spruce, western hemlock, and Lowland fir grow- ing in light intensities from 0.021 to 0.029. The western larch however showed only poor development in a light intensity of 0.353. This will be sufficient to indicate that the light in the dense shade tent compares with some of the lowest light intensities that have been measured in our western forests. In this con- nection it is interesting to note that white pine, black locust, red oak, and western yellow pine lived for two to four mouths in the dense shade tent, as is evidenced by the fact that stem and root measurements were taken on these species during the last days of these investigations.
In connection with the light experiments a very important fact soon became evident. In spite of the fact that all three cultures were watered every evening at the same time and in the same degree, it soon became evident from mere observation that the top layer of soil by the following evening had dried out to very different degrees in the three cultures. The open light culture was noticeably the driest and the dense shade culture the moistest so iar as the top layer was concerned. This fact led to taking systematic moisture samples to determine the exact difference in moisture content. These samples were taken once a month, three evenings in succession and these readings were averaged into one reading. The table of soil moisture contents is given below:
28 Richard H. Boerker
Taste or Sort Moisture Content 1n Licut Cuttures 1N Per CENT.
Depth’2 cm. 7 Dates . | Open Light Medium Shade Dense Shade TOTO AT 2 dooce saves @riciiahiand 2 | 12.3 Ti5i3 19.8 PEIOE Ei ocnd neh nwimeeaees : 12.0 19.0 ses Oe DS Nis 1 pte a igen eiadonce A 6.1 i697 18.0 DEPARUG: ox an pawn ate einen x 14.0 16.6 Dis BUDAST Os oie pace henge gessinantes 14.4 17.0 21.3 BITS E Pos se bee eerie ies 10.3 E72 | 19.7 AVGTAGE sews es caewnges winded _ Ins 16.8 | 19.9
Soil depth was comparatively easily controlled, either by only partially filling the flats with soil or by using deeper boxes. This was done and the depths used were as follows:
SHAG SOIl cicseahtnhad aa eda wdale eens oo oReGaen nein 4.0 cm. Mie ditirit. Gee p: S61 ssc as tis trace asec anavontbinusuelgih besser oveenlars 9.0 cm. Wer yodeep. SOtl ctccadescos ates. wij lorensearcuana taastica ie averseonsrerars 30.0 cm.
The depth of the medium soil was the depth of all the other cultures used in the light, soil moisture, and soil texture experi- ments. No attempt was made to measure the soil moisture con- tent periodically in the soil depth cultures, except as noted in checking up the watering of the cultures.
Soil moisture was controlled in the soil moisture experiment by watering the cultures at different intervals. The wet culture was watered every evening, the medium wet culture was watered every Wednesday noon and Saturday evening and the dry soil culture was watered only every Saturday evening. The soil samples that were taken were secured just before watering and were taken at first every Wednesday noon and every Saturday evening and later only every Saturday evening. Thus the soil samples represent the minimum water content of the soil at the end of one day, at the end of three and one half days, or at the end of seven days. In the following table are given the soil moisture per cents as taken at various, depths according to the stage of development of the majority of the seeds or plants in the cultures concerned.
Germination of Forest Trees
Minimum Sort Morsture Content 1n Sort Morsture CuLtures
29
f ium Wel Date a. | ee ee | TDA ten ses pnccastegna end 2 o-§ 6.4 10.5 23.0) DD Pre Gs Awa ausdubiscwiae Wd a2 0-5 4.0 | rie es 30.0 T/T LE ied de rasnn edtantad esi 0-5 4.6 5.0 25.0 5S 0) (ye ee 0-5 22 14.1 24.1 Tse) 2 Dewireoestnece vse cronstse has 0-5 7-7 17.1 21.0 TED Bisa sats ais as atigeenn ya 0-5 64 13.8 2253 POF haw ed oe 0-5 Git 12.4 2453 T2/tOe no ees a a cine ey 0-5 8.5 16.6 ee: 200s — eek ee kad eLabe> 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 <a ieee n'a ewe eH eG 0-5 5.9 ' 14.0 30.8 AIDG scleiows bncenwk b* 0-5 a8 8.0 23.8 MI2A oe hcodich Bees 0-5 4.0 Toa 207 Average........... 7 | cee TL 8) 23.9
Soil texture was controlled by the use of cultures of loam, sand, and gravel. Soil texture affects principally the moisture content and the air content of the soil, hence careful analyses to determine both relations were made. determinations were made for sand, loam and gravel, which show the amount of hygroscopic water, the volume of pore space, and the amount of capillary water in each of these soils:
The followi
Tas_e or Sort DETERMINATIONS
ng moisture
Hygroscopic Water,| Volume of Pore’
Capillary Water,
Texture of Soil Per Cent Space in Per Cent Per Cent Gravel, GHGs s gawdpusexauces 26.54 Lae MeEdlUths..- swiss wees 0.14 39.34 5.0 CORTES: ¢ hives twa & 41.14 2.8 AVETAREnosce cece ae a 39.04 4.4 I koa eosin’ nice SEER ERR OPT 33-51 16.6 TSO aly, 2. 44. 58 ae edationen sg Bea 0.92 53.32 38.0
1 Lost by accident in the soil oven.
30 Richard H. Boerker
The per cent. of hygroscopic water in the soils was the amount of moisture the soils held at room temperature. The amount of pore space in the soils was equivalent to the total amount of water the soils would hold. This would also be the amount of air in the soil when air dry. In determining the amount of pore space the soil used was air dry, hence the amount of hygroscopic water in the soil had to be added to the amount of pore space. The amount of capillary water was the amount of water the soils held against gravity. The same soils were used in all three experiments and the samples consisted of about 150 grams each except in the volume determinations in which 100 cubic centi- meters of soil were used in each case. This table shows very strikingly the water and air relations in these soils. The great amount of air in gravel when it is at its maximum capillary water content is also shown approximately.
The mechanical analyses of representative samples of these soils which were kindly furnished by the department of agronomy of the University of Nebraska are given below:
MeEcHANICAL ANALYSIS OF SOILS
Separate | Diameter, Mm. Loam Sand Gravel
Ores wees Vee eyes Ese BOOVES 4 weeae & genes 38.639 Coarse gravel... ee nee Baz eases ll) Seta 40.382 UME STAVE icc, sey costa 2h Sugso vuseneved 2-1 7.936 21.045 I4.051 COOTER SANG oss se ce we own I-.5 TL.771 29.418 4.245 Medinm 6400 we iaeaee eau 5 25 8.197 21.709 1.062 BAN na 4 seieici ere ti arm rare anes .25 —.1 II.392 25.708 0.770 Very Hime ead ss osc ansanncccon L005 6.182 1.074 Se ee a ee er rT .05 —.005 | @ievow 0.268 1s eee ee ee ee rT .005 and less | 26.566 “nae Vola tOBUter secs eeeveneets| 26 eece a chen 6.252 | 0.700 0.583
a od ici 5 Bd bck ammo Lasik, kena tte dak 100.000 | 100.000 | 100.000
Besides these determinations soil samples were taken once a month to determine how much moisture these soils held at the end of a day in the cultures in the greenhouse. These results bear out the findings in regard to capillary water held by the soils shown in a preceding table. These moisture contents are given below:
Germination of Forest Trees 31
Sort Motsture ConTENT Twenty-Four Hours Arrer WATERING Depth 5.0 cm.
Date | Loam, Per Cent | Sand, Per Cent Gravel, Per Cent DL AAs sedeensi a eodvareue tenons a5 | 4.3 2.4 Tid UG heas se. aria aise dat daoecnca a aio 25.6 5.4 2.1 TDS vp asccainsing sa gtosarsp spay a5.r 4.8 2155) O/T Sate uinhtinls vygor ves oe 26.2 5.0 2.0 2 TG samacrse an teas kaa 28.7 $a 2.4 GUS py Meeks 84a eas AES 274 4.9 | 1.9 PO Boe aud bbs ghd db steouens ; 26.8 4.9 | a2
The temperature and humidity of the air were determined by a hydrothermograph which was checked every Monday morning by means of a cog psychometer and humidity tables (the baro- metric pressure used was 29 inches). The record sheets were summarized and the results for the entire period are given below by weekly averages:
Temperature, Degrees Fahr. Relabye el Week Ending Veek : ; Min. | Max, | Weekly Mon Min. | Max. ee Range} 2 Hr. 2Hr. INOMCMBER” hh .a.o.esanidensigubacs 60 100 40 71.7 18 78 49.0 Bs ditudt 8G oh lacskidean 53 99 46 67.9 34 93 69.4 AAG vA Gre cana ite an pln 52 94 42 67.8 20 90 64.0 DD Fe caine tarconcaftsseshe Ai ehe 49 90 4r 66.6 29 | 75 54.9 QO se nies a wnt aie deeecetes 54 90 36 67.2 21 1 75 . 55-9 December O24 ss6549 64 4a 59 890 30 70.2 32 | 84 ! 60.7 ES: ps eaeee ved ees 59 87 28 69.7 37 | 66 55.0 BO iocmnee cre bx mS 52 83 31 67.8 38 | 62 | 48.9 225 eae ieee 5 88 37 67.0 35 57 48.8 January Bs Lh dues esi ead Ge weneiecw 56 93 37 72.9 34 69 . 52.8 BO soja dx deren cedctens 52 890 27 67.3 4I 79 | 64.7 GBs os peat wie ie es Si 85 ar 64.6 30 #6 | Gait DD a sets tar icsevenie dap BS ash 47 96 49 65.4 39 75 58.5 Blind gp ae wesendshersieti 53 88 35 64.6 43 | 82 65.7 February Feuchsaug aa actss 53 98 45 70.4 33 | «+68 54.5 Tnechs tees seein 57 98 4r | 68.4 38 78 62.2 Piles oc eees oh awe 52 95 43 61.5 on 85. 717 BR soe emathad & ako 55 98 43 | 64.9 25 65 54.0 March TES 3 Sr Sabi vinisa east sacle 57 100 43 | 63.2 21 60 | 53.7 DA ces cosp Souk tal Sos 54 98 | 44 | 65.5 28 65 54.6 C1 ee eee aaNet 59 100 AI 67.4 22 63 50.5 DG yaa as toencdee ees 54 100 46 | 63.7 28 83 62.0 April shee 's ararasasan. 5-10hoh 53 100 47 | 66.6 23 88 55.7 Ties ee ee gen sey 55 100 45 64.5 23 61 47.2 CSiccs oe ress s eee 47 100 53 64.6 18 85 49.9 VA een a erie 49 100 51 9332 24 90 68.3 May DE tee Ads a 61 100 39 75.0 18 92 63.0
32 Richard H. Boerker
Soil temperature was not measured. With the air temperature at an optimum point during the entire experiment it is reasonable to assume that the soil temperatures were likewise always at an optimum, at least they were never at such a low nor at such a high point so as to affect materially the germination of the seeds or the growth of the seedlings.
Notes on Damping-Off
No special investigations were conducted to determine what species were most affected and what conditions of light, moisture, and soil were most favorable for the development of this group of fungous diseases. This part of nursery practice is a problem of no small importance in itself and the only data here given is that which had to be taken in connection with this series of in- vestigations. Therefore these are merely notes and suggestions, which, while conclusive as far as they go, must be substantiated in the future to be of any permanent value.
It was found that the pines were most affected. Pinus divari- cata at the end of five weeks was affected most. About 15 sepa- rate cultures of 200 seeds each of this species were started and most of these showed more or less serious effects of the disease. Several cultures of Pinus rcsinosa failed after six weeks. Pinus palustris damps off in loam before it really gets its crown above ground. In this case the loss was reduced in the sand and gravel cultures. Both the New Mexico and South Dakota varieties of Pinus ponderosa after five weeks damped off considerably, leaving only from 10-25 per cent. of the original stand. The following is a list of species in the order in which they were affected in loam under normal conditions of light and water. The first men- tioned were affected most:
Pinus divaricata Pinus ponderosa (N. M.) Pinus resinosa Robinia pseudacacia Pinus palustris Pinus strobus
Pinus ponderosa (S.D.) Pinus taeda
It appears that the seeds of trees of certain habitats when germinated in soils or under conditions different from those ob- taining in their natural environment are affected worst. These
habitats are:
Germination of Forest Trees
1. Sandy soils Pinus divaricata Pinus resinosa Pinus palustris Pinus taeda 2. Dry habitats Pinus ponderosa (S. D.) Pinus ponderosa (N. M.) 3. Poor soils Robinia pseudacactia.
33
f i
13 L iu oF 5 zeae tH =e fee if aecaieeiia arsed = eis Serre eer ye FH LARTER SP Pare A + t an t i: Va H 7 i +t f AC : H ist rH sia tt Bye ste eal : + tt t 62 — inns ime oe : + if it - ; i Peo inv anode Poet Pt rH
34 Richard H. Boerker
Species that seemed to he affected most were those from the Black Hills and New Mexico and those affected least were those from the Pacific coast. Intermediate between these were those species obtained from Montana and Idaho. The coast species affected most was Scquoia washingtoniana. Pseudotsuga taxi- folia was much less affected than Pinus ponderosa taking into ac- count all the varieties of each.
The conditions and cultures which were favorable to damping- off are of interest in that they emphasize many points already known about this part of the subject. Loam is more dangerous than sand or gravel due to its moisture retentiveness. The shade cultures were more affected than the open light due to a greater soil moisture content in the upper layers of soil. The moist cul- tures were affected more than the dry ones and the shallow soil cultures more than the deep soil ones due to a greater amount of soil water per unit of volume of soil. Humous soils, soils with decaying vegetable matter, and manure soils should be avoided because they contain myriads of fungus spores. The data for Pinus divaricata is given as representative of the three worst affected species. The per cents. given below are those of the number of plants killed (out of the total number that germinated) within five weeks after planting the seed. Two hundred seeds were planted in each culture:
Pinus divaricata KILLED By DAMPING-OFF
Light Cultures | Soil Moisture Soil Depth ' Soil ‘Pexture Open. gsgunes ge), Dry soils eds in. ¢ 0% DEED iveniicetis soeve 8% Loam......... 335% Medium..... 26% Medium soil...24% Medium....... 35% Sand Nene ee To Deéns@i: xo. < 90% Wet soil....... 35% Shallow....... 61%iGravel.... ... 0%
THE EFFECT OF HABITAT FACTORS UPON GERMINATION
This problem was undertaken because it was felt to be of funda- mental significance not only to silviculture but to ecology as well. Not only was it desired to throw more light upon some of the phases of this problem that had already been partly worked out and to modify, if necessary, some conclusions that have been drawn, but it was my intention to throw some light upon phases:
Germination of Forest Trees 35
of it that had never been attacked. Some of the questions that are immediately called to mind by a mere statement of the prob- lem are: Does light affect germination in any way? Does light affect the germination of tolerant and intolerant species differ- ently? How does soil moisture content affect germination? Do drought-enduring species and moisture-loving species behave alike in this respect? What is the effect of soil texture upon germination? Has the amount of air or oxygen in the soil any significance in germination? Since soil texture affects mainly the moisture content of the soil, does soil texture affect drought- enduring species in the same way as moisture-loving species?
The data collected upon the effect of habitat factors on germina- tion will be presented in four parts. The effect of light, soil moisture, and soil texture will be taken up in the order named and following this there will be given a résumé of the relative effect of all habitat factors. The three most important points to be noted in germination, are the number of days it took until germination began, the total number of days in the germination period, and the final germination per cent. The rate of germina- tion is shown by curves for certain representative species. The length of the germination period was taken as the total number of days during which any seeds germinated. Records were kept long after germination ceased, so that the germination period was ended at the time the last seed germinated. To give data as to the period of greatest activity involves certain arbitrary standards and this method, though tried in compiling the present data, was abandoned. The effect of light, soil moisture, and soil texture upon the periods of greatest activity is best shown by the curves offered for certain representative species.
The original data was taken by two-day periods. Every other day the number of seeds that germinated were counted and re- corded. In most cases these were immediately pulled up; but where growth measurements were to be taken later the seedlings were allowed to grow.
The first three tables show the effect of light upon the germina- tion of eastern species, Rocky Mountain species, and Pacific coast species respectively. Three sets of figures are given under each
36 Richard H. Boerker
degree of light, namely, the number of days which elapsed before germination began, the number of days in the germination period, and lastly the final germination per cent.
The number of seeds used of each species in each culture made was as follows: roo seeds each of Catalpa speciosa, Acer rubrum, Gleditschia triacanthos, Pinus taeda, Pinus ponderosa (Idaho), Abies grandis, Abies lasiocarpa, Pinus ponderosa (Mon.), Pinus ponderosa (Harney), Pinus ponderosa (Calif.), Pints jeffreyi, Pinus lambertiana, Pinus coulteri, Abies magnifica, and Pseu- dotsuga taxifolia (Wash.) ; 25 seeds of Quercus rubra, 400 of Betula papyrifera, and 200 seeds of all other species.
When a number of check cultures were combined as was noted previously it became necessary to average the results obtained in several cultures under the same set of conditions. Thus the check cultures used in each series show the same data in every case. Three cultures of each of the following species were averaged together: Catalpa speciosa (Ind.), Pinus strobus, Quercus rubra, Pinus divaricata, Robinia pseudacacia, Betula papyrifera, Pinus ponderosa (S. D.), Pseudotsuga taxifolia (N. M.), Pinus pon- derosa (N. M.), and Pinus ponderosa (Calif.). Two cultures of each of the following species were averaged together: Pinus palustris, Pinus resinosa, Pinus jeffrevi, Pinus lambertiana, and Pinus coulterit. All other species in the check cultures were planted but once.
In Table I 10 species out of a total of 14 germinated in the dense shade before they did in the open light culture. Only one species, Pinus palustris, germinated first in the open light, one species, Gleditschia triacanthos, did not germinate in the open light at all, and two species germinated simultaneously in all three cultures. Pinus strobus germinated 8 days earlier in the dense shade than in the open light, Pinus divaricata 2 to 4 days, Pinus resinosa 10 days, Pinus taeda 2 days, Catalpa speciosa 2 days, Quercus rubra 14 days, Robinia pseudacacia 2 days, and Acer rubrum 4 days.
In 9 cases the germination period is longer in the dense shade than in the open light and, considering the shade cultures together,
Germination of Forest Trees 37
II species show a longer germination period in the shade than in the light. The other three species did not germinate suffi- ciently to make a conclusion possible,
TABLE I Tue Errect or Light on GERMINATION
Eastern Species
Open Light Medium Shade Dense Shade
Species Began,} Period, Aine Began,| Period, inal Began,| Period, Haale
Days | Days | Cent | Days) Days | Cent | Days | Days Cone
PIRUS SIOOUS . scwenews 22 50 10.7 | 16 54 Ties: | my 26 8.0 Pinus divaricata....... I2 32 54.5 | 10 26 :63x5:| TO 38 73-5 Pinus divaricata (F.S.)| 14 20 | 39.5] 14 26 |37.0| I0 24 | 46.5 PMS PESOS soe 9 stn ads 24 16 | 30.5 | 16 24 150.0] 14 14 | 74.5 PINUS POLIS 3 5 suka ai eo | 20.5 | 32 $2 | 72.0 | 32 62 55 PURUS tC dO ss o.5)0.4 so 34 6 19.0 | 34 6 | 330] 32 8 | 33.0 Abies balsamea....... 18 30 | 11.0] 18 38 |10.0] 18 36 8.0 Catalpa speciosa....... 18 I I.0 fe) fo) 0.0] 16 Be I.0 Catalpa speciosa (Neb.)| 16 12 |OD.0 | TZ. | 20 | 62-07) 24 14 | 88.0 Queer CUS) LUDIE ccs i crsearace 40 28 28.0 | 30 18 12.0; )| 26 42 I2.0 Robinia pseudacacia... 8 16 | 28.8 6 18 | 29.0 6 18. 3355 Betula papyrifera...... 34 I T0:| 34 I 2.0| 34 I 1.0 ACO VUOTUM sxactan\iasa.s 18 30 17.0 | 16 34 I5.0| 14 34 16.0 Gleditschia triacanthos . to) (o) 0.0 6 2 2.0 6 2 2.0
Three species had a higher germination per cent. in the open light than in either of the shade cultures. Four showed the highest per cent. in the medium light and six in the dense shade. The greatest difference was shown in the case of Pinus resinosa whose germination per cent. was almost two and one half times greater in the dense shade than in the open light culture.
The germination curves of Pinus resinosa and of Pinus divari- cata are given on page 38. These are representative of the effect that light has upon germination. These curves show a greater germination per cent. in the dense shade culture, a more rapid rise of the germination curve in the dense shade and that germination begins sooner in the shade than it does in the light.
38 Richard H. Boerker Tue Errect or Light upon GERMINATION Stones ty
ae = +44
et Wier
a Uy HE z ernie cast Fic.1. The germination curves of Pinus resinosa.
# ar iH ee cecae rH
Fic. 2. The germination curves of Pinus divaricata.
Germination of Forest Trees 39
TABLE II Tue Errect or Light on GERMINATION
Rocky Mountain Species
Open Light Medium Shade | Dense Shade
o 2
Species a By. |e | ee | Bee ew coe an a |e
& |BE|28/ 86/88 22) 85 | B2| 82) 2d
BA) RO )e gga ES ey |e AO Pinus PONTE OS 654s een ¥ 4 $.D. TO | 32 |58.0| To #2 | 56:5 10 | 34 | 58.5 Pinus PONGETOSO ssc ccipdcre Harney. 14 | 14 |524) 8 26/580 8 | 26 | 6706 Pinus ponderosa.......... N.M. | 14 | 40 56.0 12 32 | 82.0 10; 12 | 79.0 Pseudotsuga taxifolia...... N.M. | 12 , 26 |63.0 10 12 | 69.0 10 16 | 65.0 Pseudotsuga taxifolia...... Colo. | 92 4217900 42 $36:,73.5 8 ° 36 62.6 ADIOS CONE oo cricw aad ne Colo. | 24 | 50 38.0 18 , 5654.0, 14 60 ' 56.0 Pinws CONDONE D5 005.asierpicarer Colo. | 14} 80 22.0 16 70 7.5 141 72! 3.5 Pinus: PONderos@s.: x60 Mon. | 18 | I2 ,10.0 18 54 '15.0 10 SBE 9.0 Pseudotsuga taxifolia...... Mon. 14 34 120.5 12 32 15.5 12! 44 | 35.0 Pseudotsuga taxifolia...... Idaho | 18 | 30 |20.5 16 64 49.0 10. 64 | 50.0 Pinus ponderosa.......... Idaho | 36 52 42.0 24: 66 52.0 14° 82 43.0 Abies grandis..........-5 Idaho | 36 36) 4.0 22 62 16.0 22 | 60 | 10.0 Abies lasiocarpa.......... Idaho | 30° 30: |..6:;6 26 50 Yo 22 28 6:0 Pinus monticola.......... Idaho | 24 50 22.5) I6 58 20.0 14 60 36.5
In Table II 12 species out of a total of 14 germinated first in the dense shade, the other two germinated simultaneously in the dense shade and open light. The number of days difference between the two cultures varied from 2 to 22 days. Pinus pon- derosa (Harney) germinated 6 days earlier in the dense shade than in the open light, Pinus ponderosa (N. M.) 4 days, Pseu- dotsuga taxifolia (N. M.) 2 days, Pseudotsuga taxifolia (Colo.) 4 days, Abies concolor 10 days, Pinus ponderosa (Mon.) 8 days, Pseudotsuga taxifolia (Mon.) 2 days, Pseudotsuga taxifoha (Idaho) 8 days, Pinus ponderosa (Idaho) 22 days, Abies grandis 14 days, Abies lasiocarpa 8 days, and Pinus monticola 10 days. The medium shade cultures in most cases represent a condition intermediate between the open light and dense shade.
In 10 species out of 14 the germination period was longer in the shade than in the light. In 6 species the germination per cent. was higher in the dense shade than in either of the other two cul- tures and in 12 cases out of 14 the highest per cent. was in either of the two shade cultures as against the light culture. In other
40 Richard H. Boerker
Tue Errecr or Light uPoN GERMINATION
ane i aera tt rH Et = : BP ed : terete i rast gras : : : : ; = ; = : H : —= i i essreens fanz: : : : : Sselosens ese } eeted had deus mace ; a t : oo : 1 es erp Fic. 1. The germination curves of Pscudotsuga taxifolia (N. M.). Spey : Be Sones bpeenees = pscsceres cones = —|. ies coese Fees needs caeseee ieees eras pepe : ae : = = a — “af a + YS : = == Boer = =H - ve —- oP ber L r t r +4 _ : x t =o po tears sszasz! jboss fegereeraa 4 : t t — 4 peek t t ic ceeoepeeaen : t 4 : | : t 7 eae i
Fic. 2. The germination curves of Pinus ponderosa (N. M.).
Germination of Forest Trees 4!
words, only 2 species had a higher germination per cent. in the open light than in the shade.
On page 40 are given the germination curves of the two New Mexico species, Pinus ponderosa and Pseudotsuga taxifolia. While these do not show a higher germination per cent. in the dense shade than in the open light they show the characteristic rapid rise of the shade curves and the fact that germination begins earlier in the shade than in the light.
TABLE III Tue Errect or Light on GERMINATION Pacific Coast Species
Open Light Medium Shade Dense Shade
2 4 ‘s
Species Suldoicssiduidgul-§.dy)/del—o§
BT AT) eS aT a ee a ae Pinus ponderosa (Calif) sass avaven 42 | 67 61.0! 22 | 92 |62.0. 22 | 62 | 42.0 PENWS JOP PENE ea cocpacnncnrs sie 4 ase Ney 3r | 77 | 22.0| 22 | 84 | 14.0] 20 | 54.| 17-0 PLAUSLGMBELH ENG: wx ccreg Stee ee 70 | 36 | 2.5! 76 | 20} 4.0) 70 | 24] 7.0 PERU COULMLET Es oacin 3 Bedied isaned. de donee Soar S2 | 4t | 1S.6) 54 | 3O | 28a) 52 | G2 | 23.0 Abies magnifica... 0.0.02 cece 44 | 52 | 18.0] 24. | 54 | 30.0) 36 | 54 | 10.0 Libocedrus decurrens........0.00055 20°) 73 | G0) ga | 18 | 426) 16 | 52] Oe Sequoia washingtoniana........... 76 | 178 | yo. 16 6 | Se) te | ta | Bs
DSUGG elerOPR YU vscerimoe:ssarinte sie tieeeriere 66 T.'|. 20.5) @: fo) 0} 0 fo) ° PPICEGESTIRENSE Shacsside ely teacseariationos n seied rier 22 | 60 |22.5| 18 | 64 | 34.0! Ta | g6 | 38-0 LSOVL%: OCCT ONLGIES sissee cera gion re Grant tsa oO} © o| 72 1 | 0.5| 70 x | 05 Pseudotsuga taxifolia (Wash.)......| 22 | 28 | 6.0) 22 | 54 | 13.0] 14 | 62 | 22.0
Out of the 11 Pacific coast species listed in Table III, 7 germi- nated in the dense shade before they did in the open light culture, 2 germinated simultaneously in the light and shade and 2 species did not germinate sufficiently to warrant conclusions. Pinus pon- derosa (Calif.) germinated 20 days earlier in the dense shade than in the light, Pinus jeffreyi 11 days, Abies magnifica 8 days, Libocedrus decurrens 13 days, Scquoia washingtoniana 2 days, Picea sitkensis 8 days and Pseudotsuga taxifolia (Wash.) 8 days.
Six species showed longer germination periods in the shade, three in the open light, and two species did not germinate sufficiently to be considered. Only one species, Pinus jeffreyi, showed a higher germination per cent. in the open light, two species showed
Richard H. Boerker
Tue Errect or Liyht upoN GERMINATION
H a i He eae ‘a ; = an 1 H+ HO L 8 : wh itt ii Hig] HME SIPRSESHHESHEESN +} = — jl io TTT = H 4 Hy N HH Be Hd gees [euue BI HTT H i HS a er ea en ie Saqngy) pee ge rH bie rH aH rege HT iN 38 es aatinaE H S TY : EEL EE TS H Fe tI rH HH i) ae 3S 4 = HTH] Wises ON = : | He Ly a ‘ SEEst w aa + tt 4 H LEA EEE HE ov HET TH fe pa aisa ies 5 rt TH 3) HH rs Sora eg Ee i} eunney ea) Sumenereiagzans rt a se i HH BS Ht i il COTTA) = REISS EC eens THT AT] fF seas vo | + ard Reaeee tecee a Ni oop LOCA ECLA rey TINY ayes THE AEA e F Hitt CH TTS = LL AE tH & HTT Bacat (eegepeeed Iteecge H 4 sess leees n Fl H PEE HERG! PEEPS fo] o H — H 1 oe Hf
The germination curves of Picea sitkensis.
Fic. 2.
Germination of Forest Trees 43
a higher per cent. in the medium shade, and six a higher per cent. in the dense shade than in the other cultures.
On page 42 are given the germination curves of Pseudotsuga davifolia (Wash.), and Picea sitkensis. Both sets of curves show that germination begins sooner, the curve rises more rapidly and the final germination per cent. is higher in the case of seeds germinated in the shade as compared to light.
TABLE IV Tue Errect or Soil Moisture on GERMINATION
Eastern Species
| Dry Soil ~~ | Medium Wet Soil Wet Soil 1g 1 e a , De en eel de eS ed ae Species iu Dey = 3) Gel Sw eS | ide | ea) o ae at Se ae | a mo | a — oe FUHUS SIVODUS 50 bio 5 ee we curnce we 8 _ | — | — | 30 | 34 | 8.0) 22 | 50 | 10.7 PINUS GIVETH O55 io. ss ces ceersntiono bees qo | 24 | fo) rq. | So | 53.5) Ta | 2 Sae5 Pimms divervcala. U8 Si.) cian yy 8% 28 | 2 | Bal ee 1 28] ql ae ) 20 |soe PRS OOMOSE yo ees 0s pe ea RAYE RS 68 I | 2.5} 24 | 40 | 49.0) 24 | 16 | 30.5 Pinus. Palustrts 2 oe iaduamannes393 es |e] 364 50) Grol 38 | 53°) TOUS PONS TCE sa kee ds Ree ERE EES —;—}]—}]—]—]— |] 34 6 | 19.0 AVES DOISOMMED 5 p48 64 bo ne heRERS —|—|—] 22 | 22 | 12.0) 18 | 30 | II.0 CGPI DE SPECOS Boon oes bd ean Ra eR SE —}—!}—}]—!1—j—] 8 Ti: EO) ‘Catalpa speciosa (Neb.)........... —|—i{—]| 22 6 4.0; 16 | 12 | 91.0 Quercus rubra.............. be GI — | — | —|] — |} — | — | 40 | 28 | 28.0 Robinia pseudacacia.............. Io ; 30 /15.0] 8 | 32 132.0] 8 | 16 | 28.8 Betula papyrifera.............. =! — | —]— | — |! — | 34 I 1.0 Acer rubrum. .0.0.... 0. ccs a4 rt 3.0 24 | 26 '12.0] 18 | 30 117.0
Tables IV, V, and VI consider the same species as the three preceding tables from the standpoint of soil moisture instead of light.
In Table IV in practically every case where a comparison is possible germination started in the wet soil culture, and was de- layed as the soil moisture content was reduced. Also the germi- nation period is shortened with decrease in soil moisture. The final germination per cent. in every case but one was highest in the wet soil. Pinus resinosa showed the highest per cent. in the medium wet soil.
This table separates the species into classes based upon their ability to germinate in dry soil, medium wet soil, or wet soil.
Richard H. Boerkcr
44 Tue Errecr or Soil Moisture UPON GERMINATION Tee tell HEPES T : ot i + t T z Seebeaes anne 2 : : ge +t : Ht HH : att 5 a : t Ht 1 = inebse tca.tash z
Fic.2. The germination curves of Robinia pseudacacia,
Germination of Forest Trees 45
According to that classification the most drought enduring are Pinus divaricata, Pinus resinosa, Robinia pseudacacia, and Acer rubrum. It is rather unusual to find Acer rubrum in this cate- gory but the seed has such a thin seed coat that water absorption is easier than in the case of a thick-coated seed. The intermediate species are Pinus strobus, Pinus palustris, Abies balsamea, and Catalpa speciosa (Neb.). Among what might be called the moisture loving species are found Pinus taeda, Catalpa speciosa (Ind.), Quercus rubra and Betula papyrifera.
On page 44 are given the germination curves of Pinus divari- cata and Robinia pseudacacia. These sets of curves show that as soil moisture decreases the beginning of germination is delayed, the germination curve rises less rapidly and the final germination per cent. is decreased.
TABLE V
Tue Errect oF Soil Moisture on GERMINATION
Rocky Mountain Species
Dry Soil fedium Wet Soil Wet Soil
vo _ - ~~
i rs fu ldol|/o§3 cul pales =n Sau | ik
a m |SE\Sbi25 ge 2bies of 22/28
APSR eg SA ce ee 28 2 les
Pinus ponderosa.......... S.D. | 26 | 26 | 26.0] 12 | 36 (48.0 10 32 | 58.0 Pinus ponderosa.......... Harney| 34 6 | 8.0 22 | 18 117.0 14 14 | 52.0 PERUS PORTE OSB 5 ck hae N.M. | 22 | 18 |39.5| 20 | 16 61.0 14 40 | 56.0 Pseudotsuga taxifolia...... N.M. | 12 6| 5.5 12 | 44 |54.0 12 , 26 | 63.0 Pseudotsuga taxifolia...... Colo. | 14 | 24; 9.5 12 | 42 |60.5 12 | 42 | 91.0 ADtES: CONCOLOP 3:6 sine ws 3 ees Colo. | — | — — 80 | 86 )Ig.6' 24 . $6 | 386 Pinus contorta............ Colo. | — | — —| 20 | 66 | 3.5' 14 | 80 | 22.0 PUARs POREEOSE. 4.0 c4 nna Mon. | —~ | — — TR | 8 1 6 al 18 | 12 | To.0 Pseudotsuga taxifolia...... Mon. | — | — —' 18 | 26 |12.0' 14 | 34 | 20.5 Pseudotsuga taxifolia...... Idaho | 24 Eo) i025. 20.) 32) | 625 18> | 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<a i iasv ns s0ea —!—f!|—|]—,—|]—] 70 | 36); 25 PINUS COUMET1 2 cee he ee ORE R ES — |—{|—] 90 8 vo) 525 4 age: | angg ABLES TING ENTICED si. cnccdse diccis oe EERE Se Se eS See | Aa | 52 | SOF Libocedrus decurrens........+..-. re. | 20 Eos.) SS 20 | 73: | 620) Sequoia washingtoniana........... el eee Gat Peon leant Kame Oe a Tsuga heterophylla..........-0405. —|—!—|—|]—/]— | 66] of | o5
48 Richard H. Boerker
CLASSIFICATION oF Species Basep uron THE Errect oF Soil Moisture UPON GERMINATION
Eastern Hardwoods
Xerophilous Species Xero-mesophilous Species Mesophi'ous Species Robinia pseudacacia Catalpa speciosa Catalpa speciosa Acer rubrum (Neb.) (Ind.)
Quercus rubra Betula papyrifera Eastern Conifers Pinus divaricata
Pinus divaricata Pinus palustris CE. $2) Abies balsamea : Pinus resinosa Pinus strobus Pinus taeda
Rocky Mountain Species Pinus ponderosa (S. Abies concolor D
Pinus ponderosa (N. Abies grandis M
Pinus ponderosa(H.) Abies lasiocarpa eens oe Pinus contorta (Id. Pseudotsuga taxifolia Pseudotsuga taxifolia N. M. Pseudotsuga taxifolia (Mon.) Pseudotsuga taxifolia Pinus ponderosa (Colo.) Pinus monticola (Mon.)
Pacific Coast Species
Libocedrus decurrens od anal Tsuga heterophylla (Calif, Pinus jeffreyt Picea sitkensis : Pinus coulteri Pseudotsuga taxifolia (Wash.)
Pinus lambertiana Abies magnifica Sequoia washington- iana In Table VI in every case where conclusions were possible it was noted that the beginning of germination was delayed and the germination period was shortened with the decrease of soil mois- ture. In every case the germination per cent. was highest in the wet soil culture. For some unaccountable reason Libocedrus decurrens ger- minated in the very dry and wet cultures but not in the medium wet one. However, the four drought resistant species stand out
Germination of Forest Trees 49
conspicuously: Pinus ponderosa, Pinus jeffreyi, Pinus coulteri, and Libocedrus decurrens, This table shows that the Pacific coast species are predominantly moisture-loving.
The foregoing table is a classification of all species used in the soil moisture experiments upon the basis of whether they ger- minated in all three soil moisture cultures, in two of them or in only one of them. These three groups are called by the terms xerophilous, xero-mesophilous, and mesophilous: Xerophilous species are those that germinated in all three cultures; xero- mesophilous species are those that germinated in the medium wet and the wet soil cultures; and mesophilous species are those that germinated only in the wet soil culture.
TABLE VII Tue Errect or Soil Texture on GERMINATION
Eastern Species
1 Loam Sand Gravel Species | ee bom =% culgn a% calda a8 , (G2 ER 2042 EP FO 42 Eh) ze (gags es SP ao ee ae mS PENUSLSINOOUS: vssascaavarirwtostiosns Wiener oes i 22 | §0 10.7] 18 | 34 | Ir.0] 34 | 38 | 7.0 Pinus GWGriCel@ scoasacwad aoe awerecaes 12 2 §4.5| 12 | 38 | 72.0} 10 | 40 | 45.5 Pies divericate (FB) en cnnews os 14} 20 39.5} 16 | 18 | 32.5) 16 | £8 | 28.0 PLUS PESINOS Dearie wien bens SERA 24 | 16 30.5| 20 | 54 | 85.0] 16 8 | 16.5 PINUS PALUSTAS ese 6s te 8% 5.5 RS 31 | 53 10.5) 26 | 54 | 12.5) 22) 62 | 9.5 AUN SHE OC OO oo acess Gr Spisasranbitay Wid Are 34 6 19.0] 28 | 12 | 41.0] 40 ¥ |) 140) ADLES DELS IME Dias yiracsdocduast OBS Srestinn ' 18 30 11.0, 14 | 34 | 18.5 TO: | 40 || 70: CGR SPCC hn ens Bw ty, Ti no © 0} 0.0} Oo 6 | 0.0 Catalpa speciosa (Neb.)........... i £6 | #2: ‘OT. 16) | 72) |-62.0) 16 I | 9.0 OUEK CUS UOT Die int spa rinclaaeipinaren Soar 40 | 28 28.0 38 | 46 | 24.0) 30 | 54 | 16.0 ROOTHIG PSCUMAONLIOs wage qe rs anne ni 8) 16 28:8 8 | £8-|39.5| 8 | 18 |-pr.5 Bede PAPI. x sxe awe eee egus® BA hay Ao} BA 2) 3.0) 34 i) 5 ACCP LUD UN 2 3%. OE RE ERHE RE AER 18 BO. 4r770;, 24 | 18 | 13.0] 78: 8 | 8.0 Gleditschia triacanthos.............- , CO) Ol Oo: 3a rl, 2ol o 0 | 0.0
Tables VII, VIII, and IX show the effect of soil texture upon the same species.
Table VII shows that for the 12 species considered in the final results only one germinated first in the loam culture. Three germinated simultaneously in all cultures, three first in the sand, and four germinated first in the gravel. Three species had the longest germination period in loam, two in sand and 5 in gravel.
50 Richard H. Boerker
Tue Errectr or Soil Texture UPON GERMINATION
FEE EEE | aap eerste : ‘ eaas iaaean tw : H sate” ui) H i Hatt wan 2, : : * pee tT ep , 4 H i peeseee a Oe ipiseas es : : Boece pesssiit 77) 3 Fic.1. The germination curves of Pinus divaricata. snee : =P ad : Ts HE : SES ote . T : tr : merce iste : ; = : : Ht + + = Be ‘Z eH : 7 eae f
Fic. 2. The germination curves of Pinus resinosa.
Germination of Forest Trees SI
The two species that stand out as having the greatest germina- tion per cent, in the loam are Quercus rubra and Acer rubrum. Nine species reached their highest germination per cents. in the sand and in this group the following stand out most conspicu- ously: Pinus divaricata, Pinus resinosa, Pinus palustris, Pinus taeda, and Robinia pseudacacia. Being species of sandy habitats it is quite easy to see why they should germinate better in the sand. In the gravel, which is a poor moisture retainer, it is in- teresting to compare such a drought enduring species like Pinus divaricata and such a moisture-loving species like Pinus taeda.
On page 50 are given the curves for Pinus divaricata and Pinus resinosda.
TABLE VIII
Tue Errect or Soil Texture on GERMINATION
Loam
Species = cul Un =8 Bh 3 ote a8
1 acta ie ee Bg Ca ipa) | ie
Pinus ponderosa.......... S.D. to | 32 58.0 8 20 57-5| 8 | 38 | 44.0 Pinus ponderosa.......... Harney} 14 | 14 52.0 14° 26 45.0) 14, 8 | 13.0 Pinus ponderosa........ . N.M. | 14 | 40 56.0| 10 26 71.5] 12° 12 | 57.5 Pseudotsuga taxifolia ... . N.M. | 12 | 26 '63.0! IO 22 70.5} 10 14 | 63.5 Pseudotsuga taxifolia...... Colo. 12 | 42 91.0 10 38 83.5| 10 44 | 80.0 AUES CONEOOM... o.oo once cus Colo. 24 | 50 38.0 18 66 51.0) 20 . 48 | 34.0 PURUS CONTOFIO. 0.0. 2o co. sso ove | Colo. | 14 | 80 22.0 20 66 19.5] 16 | 70 | 40.5 PINUS PORAETOSE. 6 oo cc ace Mon 18 | 12 10.0 18 48 tI1.0) 18 ieee | 4.0 Pseudotsuga taxifolia...... Mon I4 ; 34 20.5 12 44 43.0' 12 , 42 44.5 Pseudotsuga taxifolia...... Idaho | 18 | 30 20:5) 20 54 111.0 16 | 70 | 43.0 Pimus POMIHOSE, 2 <6 e446 ed | Idaho | 36 | 52 43.0 44 | 52 |59.0 20, 78 | 71.0 ADS PIONETS oo 5.2% 24 en ee | Idaho | 36 | 36 4.0) 46 | 61 2.0 36 | 30: | 3.0 Abies lasiocarpa.......... | Idaho | 30 | 30 | 6.0; 0 | 9/0 0! 0 ° Pinus monticola.......... ' Idaho | 24 1 50 |22.5' 24 | 50 |11.5 24 50 !13.5
Table VIII gives the results for the Rocky Mountain species. Out of 13 species, 8 germinated first in sand or in gravel, only one germinated first in loam, and four germinated simultaneously in loam and in sand or gravel. Eight species show a longer period of germination in sand or gravel than in loam, and 5 species show the same length of period in either sand or gravel and in loam. Six species show a higher germination per cent. in
$2
Richard H. Bocrker
Tue Errect or Soil Texture upoN GERMINATION
anen:
aH a Fic.1. The germination curves of Pinus ponderosa (S. D.).
Fic.2, The germination curves of Pinus contorta,
53
ea
Germination of Forest Trees
Tue Errect or Soil Texture UPON GERMINATION
The germination curves of Pseudotsuga taxifolia (N. M.).
The germination curves of Pinus ponderosa (N. M.).
Fic. 1.
IG! 2;
54 Richard H. Boerker
loam, four in sand, and four in gravel. It is significant to note the large number of species in this table that germinate well in the gravel.
On pages 52 and 53 are given the germination curves of Pinus ponderosa (S. D.), Pinus contorta, Pseudotsuga taxifoha (N. M.) and Pinus ponderosa (N.M.). These curves show that the germination usually begins earlier in the sand or gravel, that the
curve rises more rapidly for these soils and that the oe per cent. is usually higher.
Table IX gives the results for the Pacific coast species. ‘Out of 9 species, two germinated first in the loam, the others ger- minated first in either the sand or gravel. Three had longest germination periods in the loam and six in either the sand or the gravel. Only one species, Libocedrus decurrens, showed the highest germination per cent. in the gravel, while six species germinated highest in the sand.
On page 55 are given the germination curves of Pinus pon- derosa and Pinus jeffreyt both from California. These curves show substantially the same facts as those for the Rocky Moun- tain species. These curves show that Pinus ponderosa does not germinate so well on gravel as does Pinus jeffreyi a fact which is significant when it is remembered that the latter will grow on much poorer soil than the former.
TABLE IX Tue Errect or Soil Texture oN GERMINATION Pacific Coast Species
Loam Sand Gravel
Species dolteol/2S)duldolo§ 3 -§
BOAO eS BA) AA eS S| ga eS Pinus ponderosa (Califa: sai aninas 42 | 67 | 61.0; 20 | 82 68.01 30 | 20 | 270 TOMS SOFIE oe soa au ao a win Rrsdrmemee's SL | 77 | 220) 26 | 86 | osm 20 | 86 4 1o:0 Pinus lambertiana........ 0.000005 70 | 36 | 2.5) 52 | 16 | 9.0] 80 | 18 | 9.0 ALDIES IAD BNE PLC Oeics ees eegiagese ribo ddan 44 | 52 | 18.0] 96 2 | 3.0; 50 | 48 | 5.0 EADIEOE EUS CECBIT CIS 6 3 acer acn sees 29 | 73 | Geo) 28 | 58 | r3.5) 28 | GS | 220 Sequoia washingloniana........... 1G | 28 | Fo) TO | 24 | r6.5| 22 2 | Os TSU20 PRODI Bias cee wage emma; 66 I | @.5| 44 | 42 | 3.0) 56 Ohl, ke PUCEGISULRENS 1S ix es 8 xia y aap het, F 22 | 60 | 22.5) 18 | 64 | 31.0} 18 | 64 | 24.5
EGV1H OCCLAEHIGIISS 2.5.5 5 dee recicdans —~—}—o—] myo} omy ey es ce Pseudotsuga taxifolia.............. 22 | 28 | 6.0) 38 | 44} §.0) 361 a8 | 60
Germination of Forest Trees 55
Tue Errecr or Soil Texture upon GERMINATION
Fic. 1. The germination curves of Pinus ponderosa (Calif.).
Coy
Ayer ere! FH
+ [ i
el t
sa
ttre Ht eat rH fr
tt tt
Fic. 2. The germination curves of Pinus jeffreyi.
56 Richard H. Boerker
Tables X, XI, and XII give the results of the effect of light, soil moisture, and soil texture upon certain groups of species as they were classified on page 48. While the foregoing tables group the species and the final results on the basis of the geo- graphical distribution of the species, these tables divide all species into three groups based upon the amount of soil moisture neces- sary for germination. The tabulation of the final data on this basis is probably more significant than any other that could be offered.
The data for the xerophilous species are given in Table X. The average figures given at the bottom of the table show that germination begins first in the dense shade, next in the medium shade, and last in the light ; that the germination period is longest in the dense shade; that, germination begins last in the dry soil; that the germination period is shortest in the dry soil; that germination begins first in the gravel and that the shortest ger- mination period is in the loam and gravel. Of the 14 species given in this table, 13 germinated in the dense shade before they did in the open, 9 showed longer germination periods in the dense shade than in the open light, 12 germinated in wet soil before they did in dry soil, 13 had shorter germination periods in the dry soil than in the wet, and 9 germinated in gravel before they did in loam.
Table XI gives the results for the xero-mesophilous species. The average figures given in this table show that germination begins first in dense shade, next in medium shade, and last in open light ; that the germination periods are longest in the medium and dense shade; that germination begins last in the medium drv soil; that the germination period is shortest in the medium dry soil; that germination begins first in the sand or in the gravel; and that the germination period is shortest in the gravel. Out of 13 species listed in this table 9 germinated in dense shade before they did in the open, 7 showed longer germination periods in the dense shade than in the open light, 12 germinated in the wet soil before they did in the medium dry soil, 12 showed shorter ger- mination periods in the dry soil and 9 out of 11 germinated first in either sand or gravel.
Germination of Forest Trees 57
The data for the mesophilous species are given in Table XII. The average figures at the bottom of the table show that germina- tion began in dense shade, followed by medium shade and open light; that the germination period is longest in the case of the dense shade; that germination began first in the loam and last in the gravel ; and that the germination period was shortest in loam. Out of the 10 species listed in this table 7 germinated in the dense shade before they did in the open light, 4 out of 8 species showed longer germination period in the dense shade than in the open light ; and 7 showed shorter germination periods in the loam and sand than in the gravel.
These three groups show exactly the same results so far as light and soil moisture go. From the standpoint of soil texture there are some interesting results. In the xerophilous species germination usually begins in the gravel, in the xero-mesophilous species it usually begins in the sand; and in the mesophilous species it usually begins in the loam, as the average figures and number of species in each case testify. In the xerophilous species the germination period is shortest in the loam and gravel, in the xero-mesophilous it is shortest in the gravel, and in the mesophilous species the period is shortest in the loam. That xerophilous species germinate sooner in the sand and gravel than in the loam is due undoubtedly to the amount of oxygen in these soils. This suggests that oxygen is more necessary for the ger- mination of xerophilous species than is the case in mesophilous ones. In the mesophilous species germination begins sooner in the loam indicating that soil moisture is more necessary to them than oxygen. In the case of the light and the soil moisture experiments it has been shown that favorable moisture conditions lengthen the time of germination. In these cases it was found that the shortest periods were in the open light and in the dry soil. This same theory is proven in the case of the soil texture experiments. It is well known that loam is favorable for ger- mination on account of its moisture-retaining properties and that gravel is favorable on account of its great amount of aeration. Sand is intermediate between these and combines enough of the soil moisture property of the loam with the aeration of the gravel
Richard H. Boerker
58
SEE [OSI |oS€ | LLr | gE |S-Lr jovgo€ |orkr | p1xr joel | vof Jorrr lovee | grex | a-ee |S-Lr [eee ‘or saseIIAy 89 4 gs gz €L 6z fe) fe) ir oz ZS QI gi ve £L Og. Pte s SUBLANIOD SNAPIIOGIT os tz os aia os bz gt gI I gb 09 vi gs ha os vz “CPI) Djosyuom snurg tr or gt or zp tae Zp aI vz vr 9f 8 9f aa fad ZI ( O]OD) p1yofixny D¥nsjopnasg ol gI ts oz of gr ze rd I bz to or v9 gI of SI |" (PI) Dyofexn] DSnsjopnasg gh O%e|; ZS Pf ca 9f can TI 8 06 zg VI 99 24 2s gE | °° CPI) vsosapuog snurg TI or oe Or gz ZI tr Zi 9 er 9I OL eI or Qz ZI | CIN) 0270faxn] D3nsjopnas qT cI zr Qz Or ov VI 91 oz gi ze 23 or Ze er ov PI | “CW ‘N) Dsodapuod snurg 8 tr gz ti vr FI gi zz 9 ve gz 8 gz 8 VI tI ‘GesureH) Dsodapuog Snutg sf | 8 oz 8 z—)} or |] of | ar 92 | oz} PE] or zz | o1 z€} or eG a °S) Dsosapuog snurg gi 8 gi 8 91 8 ze 8 of or gI 9 gi 9 QI g “piapIvpnasg DIULGOY 8 gi gi vz of gi gz Ee I vz ve vI ve QI of Qi [18S > 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
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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<ormvegaaniesensdanaeeen anaes meron 4
AUSO LAL | rst cocoa claps tener eon one eee omen eiere tle ho te 37
The distribution of these species in the three groups as de- termined by soil moisture is not significant. The only interesting fact to be found is that no mesophilous species germinated highest in the gravel.
TABLE XIII SuMMary OF THE Beginning of Germination By NUMBER OF SPECIES Light Number of Species Germinated First in Sthvesmeca Total Xerophilous Ghilous Mesophilous Oper LIB. 5 ciereerccsr a aise 0.33 | 2533 0.50 Bony Medium shade......... BES3 | 2.33 ' I.00 5.67 Dense shade........... 11.34 8.33 5.50 25.16 j } Totals .ecusyeeanea es 14.00 13.00 7.00 | 34.00 Soil Moisture ID EyASOi 2... wAcauswndnicouslactle 1.33 abke sevens 1:33 Medium wet soil....... 3.83 0.50 odo, 4.33 Wie 60h .c nau erasiecmas 8.83 12.50 Sistas 2.34. LGtalsis vx ecwseaer hia 14.00 13.00 aria | 27.00 Soil Texture OD abe M Ad wok abies 2.50 ery i e206 | 0% Sand. coca 23 eevee 5 4.00 al7 | 3.00 | T207 Graven Aacacecnmnende 7.50 3.66 | I.50 12.66 i Ota ls sy ecvesene tae evant i 14.00 II.00 | 7.00 l 32.00
62 Richard H. Boerker
Tables XIII, XIV, and XV take the same data as presented in previous tables but the results are given by number of species rather than by average numbers. The number of species in each group which performed certain things under certain conditions are given without respect to the name of the species. This is perhaps a better way of drawing conclusions than to use average figures. Each species is counted in its proper column; if a species, for example, germinated simultaneously in two cultures it counted one half in each column.
TABLE XIV Summary oF THE Length of the Germination Period By NUMBER OF SPECIES Light Number of Species Shortest Germination ial Total Herod 10 Xerophilous ee Mesophilous Open lights csr e aureceteay 7.00 5.00 2.50 14.50 Medium shade ........ 4.50 3.00 3.50 : II.00 Dense shade........... 2.50 5.00 I.00 ; 8.50 POA eso one Bea a 14.00 13.00 7.00 ' 34.00 Soil Moisture TP GO oc oh ven nmianndeielern 12.00 Fer | 12.00 Medium dry soil... 2. I.00 I2.00 ah C63 13.00 Wetesoills. 2 cca wena 1.00 ' 1.00 | apis ; 2.00 1 MOtall.y. 3 ste ges iaaintata andes 14.00 13.00 j 27.00 Soil Texture
PSA se sh Sich Shek oi pttatntate 3.83 4.00 3.00 | 10.83 SAN acs aesesetetyapiriorcotresitere 4-33 3.00 2.00 | 9.33 SANE ircx.sayt asvsitonstieete aieeaed 5.83 4.00 2.00 | 11.83 Po tall scien ieaighenaesinene 14.00 | II.00 | 7.00 32.00
Out of 34 species 31 germinated first in either of the two shade cultures and only 3 began their germination in the open light. The tendency to germinate first in the shade is more marked in the case of the xerophilous and the mesophilous species and less marked in the xero-mesophilous. Out of 27 species,
Germination of Forest Trees 63
over 21 germinated first in the wet soil. In both the xerophilous and the xero-mesophilous species the tendency is to germinate first in the wet soil. In the experiments on soil texture the tendency is for the xerophilous species to germinate first in the gravel and sand, for the xero-mesophilous to germinate first in the sand, and for the mesophilous species to germinate first in the sand and loam. This is a most interesting result, in view of the moisture and air conditions in these soils. On the whole the tendency is for most of the species to begin germinating in the sand and gravel; about 25 out of 32 species began germinating in either of these two kinds of soils. In the soil texture data it is interesting to compare the germination of xerophilous and meso- philous species in the gravel. Such a comparison shows 7.50 xerophilous species germinated first in the gravel and only 1.50 mesophilous species.
From Table XIV it is apparent that out of 34 species 14.5 showed the shortest germination period in open light and that the number of species of this kind decreases as the intensity of the light decreases. In other words shade increases the length of the germination period. In the soil moisture experiments the shortest periods were in 25 species out of 27 found in the dry or the medium wet soil. In the soil texture experiment the species are very evenly distributed. Loam and gravel, the two extreme soils from the standpoint of soil moisture and soil aera- tion, show the greatest number of species and the sand culture shows the least. This fact is in harmony with the idea that favorable conditions, such as we found in the light and the soil moisture experiments, lengthen the period of germination.
Table XV shows that out of 14 drought-enduring species 12 reached their greatest germination per cent. in the shade; out of 13 xero-mesophilous species 10 reached their highest per cent. in the shade; and out of 8 mesophilous species 7 reached their highest per cent. in the shade cultures. Out of a total of 35 species, 29 germinated highest in the shade cultures. Out of 27 species tried in the soil moisture experiments 23 germinated highest in the wet soil and 4 highest in the medium soil. None reached their highest per cent. in the dry soil cultures. Among
O4 Richard H. Boerker
the xerophilous species the highest per cents. are in the loam and sand, among the xero-mesophilous species the highest per cents. are in the sand while in the mesophilous species the highest per cents. are in the sand and loam. Out of 34 species, 18.5 ger- minated highest in the sand, thus showing the value of this class of soil for seed germination.
TABLE XV SUMMARY OF THE Final Germination Per Cent. By NUMBER OF SPECIES. Light | Number of Species Greatest Germination i Per Cent in ; Xeromeso- : | Total Xerophilous philous Mesophilous | | ie ca ne 2.00 3.00 1.00 6.00 Medium shade......... 3.00 7.00 2.50 $2.50 Dense shades ¢s-¢20g¢a04 9.00 3.00 4.50 I 16.50 Dt os oc ee eyau umes 14.00 13.00 8.00 35.00 Soil Moisture TI SOM si 6 22 sgnctotueveseuarius 0.00 ds dette 0.00 Medium wet soil....... 3.00 1.00 en 4-00 Wie tes Ola sive etecaneceseitenabates II.00 I2.00 ines 23.00 Otis és ana ccetet as 14.00 13.00 eae 27.00 Soil Texture 5 OF 21s, eee ee ae 6.00 1.00 2.50 9.50 SANG: ses cust ge essed eyacdeauetieud 5.00 8.00 5.50 18.50 oy er eee 3.00 2.00 1.00 6.00 Eis: a ancora eaten 14.00 11.00 9.00 34.00
THE EFFECT OF HABITAT FACTORS UPON STEM AND ROOT DEVELOPMENT
Following the experiments upon germination, some of the species were grown for several months for the purpose of ob- taining root and stem measurements. Since damping-off re- duced materially the number of seedlings as time went on, the number of plants upon which final measurements could be taken was naturally reduced. Hence the results are not based upon as many measurements as was originally intended.
Germination of Forest Trees 65
The species retained for this work were Pinus ponderosa (S. D.), Robinia pseudacacia, Quercus rubra, and Pinus strobus. Stem and root measurements were taken upon the first three of these species and stem measurements only upon the last one. Each measurement represents the average of 10 representative plants, except in case of Quercus rubra where from 3 to 14 plants were used depending upon the number available. The measurements of the stems of Pinus ponderosa and Robinia pseudacacia were taken at two different ages, namely at the age of two and three months, but the plants used at the age of three months were not the same ones used at the end of two months. Hence in the data the three months’ old plants are not necessarily larger than the two months’ old plants, although they usually are. Root measurements of Pinus ponderosa and Robinia pseudacacia were taken at the end of three months. Both stem and root measurements for Quercus rubra were taken at the age of five months.
The effect of light on stem and root development is shown in the following table:
Tue Errect or Light on Stem AND Root DEVELOPMENT
Conifers Stem Measurements Root Measurements P. ponderosa P. strobus | P, ponderosa (3 Mos.) Degrees 2 Mos., 3 Mos,, 2 Mos., Tap, Laterals, Cm. Cm. Cm. Cm. Cm. Open HONE. sioanee vee ees 2.76 2.59 4.31 5.08 baa Medium shade............ 2.90 3313 5.50 5.80 -62 Dense shade.............- 3-50 6.35 wed stents Hardwoods Stem Measurements Root Measurements (Tap) R. pseudacacia Q. rubra | Rob. pseud.| Q. rubra Degrees 2 Mos., 3 Mos., 5 Mos., 3 Mos., 5 Mos., Cm. Cm. Cm. Cm. Cm. Open lighbnn svspsaacalanins 6.00 7.02 9.40 9.64 13.8 Medi shad@s «0c ansnse 5.80 5.95 20 7,16 10.2 Dense shade.......------- 5.00 5.52 | 8.00 5.69 10.2
66 Richard H. Boerker
From these tables it will be seen that Pinus ponderosa increases its length of stem with a decrease in light intensity both at the age of two and at three months. This is likewise true for Pinus strobus. For Robinia pscudacacia, however, both at the age of two and three months, there is a striking decrease in stem height with a decrease in light intensity. Quercus rubra behaves the same way, except that the length of stem is greater in the medium shade than in the dense shade. This development is shown very well by the accompanying photographs.
In the case of all species it is strikingly shown that the length of the tap root and the total length of the laterals decrease with decrease in light intensity.
In so far as the stem and its relation to light is concerned it is quite evident that hardwoods behave differently from conifers. As has been pointed out conifers tend to increase their height growth with decrease in light intensity while hardwoods tend to decrease this growth with decrease in light intensity. Evidently conifers can adapt themselves to these unfavorable light condi- tions better than hardwoods. In the hardwoods the reciprocal relation of roots and stem in their dependence upon light is strik- ingly shown.
Tue Errect or Soil Depth upon Stem and Root DEVELOPMENT
Conifers Stem Measurements Root Measurements Degrees Soil Depth Pinus pond. P. strobus | P. ponderosa (3 Mos.) 2 Mos., 3 Mos., 2 Mos., Tap, Laterals, m. Cm. Cm, Cm. Cm. Deep erases ie aseeh asia rlinp asta Sons 18 2.85 2.69 4.35 9.51 7 MC GiUItis. ctns cin caseagenseliggins 2.96 2.59 4.31 5.93 IsTT Shallow swim cuntieiiscedne 2.60 2.68 4.25 3.97 4.61 Hardwoods Stem Measurements Root Measurements(Tap) Degrees Soil Depth R. pseudacacia = Q. rubra | Rob. pseud.| Q. rubra 2 Mos., 3 Mos., 5 Mos., 3 Mos., 5 Mos., Cm, Cm. Cm. Cm, Cm, Deep ee 6.45 7:20 6.50 15.55 20.4 DIA ved oadnuew acy 6.00 7.02 9.40 9.64 13.8 AON, « v0 4 594 Boy ba een 5.70 6.04 5.90 3.30 6.9
Germination of Forest Trees 67
The foregoing tables show the effect of soil depth upon root and stem development for the same species and ages of stock.
In the case of stem development in all species except Quercus rubra, the height of the stem increases with increase in soil depth, The increase in length between the deep soil and the shallow soil is not very great, 7. ¢., in the pines it is never over 0.25 cm. and in Robinia it is never over 1.16 cm. In Quercus rubra the smallest height growth is in the shallow soil but the greatest height growth is in the medium deep soil. It is interesting to note that in all cases the greatest total length of stem and root together is in the plants grown in deep soil.
As is to be expected the length of the tap root is materially decreased as the soil depth decreases. In Pinus pondcrosa the tap root is 24 times longer, in Robinia it is 5 times longer and in Quercus it is 3 times longer in the case of the deep soil than in the shallow soil. The length of lateral roots was taken only in the case of Pinus ponderosa and this species is representative of what took place in all the other species. In this species the total length of lateral roots increased with decrease in soil depth. In the case of Robinia this is strikingly shown in the photographs. This indicates that whether a tree has deep-seated roots or super- ficial roots depends largely upon the depth of the soil in which the tree grows. The terms “ deep-rooted species” and “ shallow- rooted species” have therefore only limited significance and the real basis for these terms is in most cases the environment.
In the following table are given the data upon the effect of soil moisture upon root and stem development :
Tue Errecr oF Soil Afoisture upon Stem AND Root DEVELOPMENT Conifers and Hardwoods
Stem Measurements Root Measurements 8
: int P. Ri Dewees Pinus ponderosa| Robinia pseud. eis P. pond. Rad
2 Mos ,|}2 Mos.,| 3 Mos.,; 2 Mos.,| Tap, Lats) Tap
‘Ga ee | Ga em | om| om. ) eae | ee DEY cs ai onececstvenoidnenghas ae oye 2.60 23 | ce 23 os | 6.004 Mediums... 4 s.usdewans 1.80 | 2.02 | 4.35 | 3-80 | 3.90 | 7.33 | 2.65 | 7.54 Wetec wuss se eauiseaarnten 2.76 | 2.59 | 6.00 | 7.02 | 4.3r | 5.03 | 1.11 | 9.64
3 Age, 3 months. 4 Age, 2 months.
68 Richard H. Boerkcr
In connection with the soil moisture experiments a very in- teresting fact was noted. Both Pinus ponderosa and Robima pseudacacia wilted on January I, just exactly two months after the seeds were sown. The soil moisture at the time was de- termined to be 6.6 per cent. It happens that at three different times the moisture content was far below this figure. On Oc- tober 28 the seeds were sown, on November 7 the moisture content was 4 per cent., on the 11th it was 4.6 per cent. and again on December 5 it fell to 6.1 per cent. Robinia pseudacacia ger- minated first on November 9 and the Pinus ponderosa on No- vember 26. It is evident from this occurrence that more mois- ture is needed for the early development of the seedlings than is necessary for germination. On the oth of January this fact was further emphasized. While taking root and stem measurements and digging up the seedlings two germinating seeds of Robinia were found. The moisture samples taken on this day show 5.7 per cent. moisture in the dry culture. As a result of this condi- tion no stem and root measurements appear in the dry column at the age of three months.
In all species measured the length of the stem decreases with diminishing moisture supply and the fact is noted that this de- crease is greater in the case of Robinia than it is in the case of Pinus ponderosa or Pinus strobus. This indicates the greater drought resistance of the conifers as compared to the hardwoods.
In the case of the root development of Pinus ponderosa it is shown that both the tap root and the total length of lateral roots increase with diminishing moisture supply. For Robinia the result was quite different, for it was found that the length of the tap root decreases with diminishing moisture. While Pinus ponderosa seems to be able to develop roots to reach the lower moisture layers of soil, Robinia is unable to do this.
The following table gives the results on the effect of soil tex- ture upon the development of the stem and roots of these species.
The greatest length of stem in Pinus ponderosa was found to be in the case of the two-months-old seedlings in the loam and the next greatest length in the gravel. In the case of the three- months-old trees the greatest length was in the gravel and the
Germination of Forest Trees 69
next greatest in the loam. In the case of Pinus ponderosa clearly the greatest length is either in the loam or in the gravel and the shortest length of stem is in the sand. Loam and gravel are, as we have seen, quite opposite when it comes to moisture retentive- ness, hence the good development of plants grown in gravel must be attributed to other properties of gravel, namely, the amount
Tue Errect or Soil Texture upon Stem AND Root DevELOPMENT
Conifers Stem Measurements Root Measurements Degrees _ Be PORTIS: _ P. strobus , P. ponderosa (3 Mos.) 2 Mos., 3 Mos., 2 Mos., Tap, Laterals, Cm. m. Cm. m, Cm. LOAM: 4s c:d.n hg, Fig RE 2.76 2.59 4.31 5-93 bie ie Sad auais wines deeds s | Bens 2.06 4.80 6.22 94 Gravels ccede 5 acensacde 2.65 2.70 4.10 7.83 4.01 Hardwoods Stem Measurements Root Measurements (Tap) Degrees R. pseudacacia Q. rubra | Rob. pseud.| Q. rubra 2 Mos , 3 Mos., 5 Mos., 3 Mos., 5 Mos., Cm, Cm. Cm. Cm. cm, POR icicle sm oats eeennoes 6.00 | 7.02 9.40 9.64 13.80 SAH Gees anasta aon eles Pris Ay 4.75 5.90 10.85 15.70 Gravelecnin ine awe eases 3.80 | 4.25 5-70 LOOTLT 16.00
of air in the soil. Pinas strobus shows the greatest height growth in the sand. Robinia shows the greatest length of stem in the loam and the least in the gravel. This is in peculiar contrast to Pinus ponderosa. For growth Robinia is evidently more par- ticular about soil moisture than about the amount of air in the soil. Quercus rubra shows the greatest height growth in the loam and the least in the gravel.
The tap root of Pinus ponderosa is of greatest length in the gravel and least in the loam, and the total length of lateral roots is greatest in the gravel. This naturally follows from the fact that, as has been pointed out before, gravel allows water to percolate rapidly and the top layers dry out very soon, hence the
70 Richard H. Boerker
plant has to go deep for its moisture. In the cases of Robima and Quercus the greatest length of laterals and the greatest length of the tap root was found in the sand or gravel, again bearing out the fact that sands and gravels are poor soils for retaining moisture.
THE RELATION OF SIZE AND WEIGHT OF SEED TO GERMINATION PER CENT. AND EARLY DEVELOPMENT
During the process of counting between 100,000 and 125,000 seeds of various kinds for these experiments the fact that seeds of the same species varied considerably in size came to the author’s notice very forcibly. In his experience in the woods as well as in seed extracting it was often noted that many factors may affect the size of seeds. In general, it may be said that the size of the seeds of any one species depends upon one or more of the following factors:
The size of the cone.
The position of the seed in the cone. The development of the cone.
The age of the tree.
. The physiological condition of the tree. The site upon which the tree grew. The climatic variety of the species.
NAW A ODA
It is an old experience that large cones produce large seeds and small cones small seeds. The seeds at the extreme base and the extreme apex of the cone are very often very much smaller than in other parts of the cone. External conditions such as temperature and moisture, may affect in no small degree the seed while it is maturing, thus retarding its morphological develop- ment. It has been observed that middle-aged trees produce the largest cones and the largest seeds, while very young or very old trees usually produce small cones and small seeds. The physio- logical condition of the tree may affect the size of the seed. Since seed crops are dependent upon the accumulated food in the tree, it is reasonable to suppose that a paucity of such food ma-
Germination of Forest Trees A
terial will produce smaller seeds than in cases where there is a great accumulation. It has been repeatedly shown that after a seed year the amount of accumulated food in the medullary rays and other food accumulation centers is reduced to a minimum. The site upon which the tree grew, naturally, is intimately con- nected with the amount of food material available for the embryo of the seed. For the same reason the climatic variety of the tree probably affects the size of the seed. At least, it is common knowledge that the California variety of Pinus ponderosa has seeds which may weigh from three to four times as much as those of the South Dakota variety. While most of these points remain to be proven experimentally, they have been indicated to the writer by various experiences and are put forth as interesting hypotheses awaiting experimental proof. Whatever the cause of the varying size of seeds is, it is quite evident from the amount of literature on the subject that this phenomenon has attracted considerable attention in recent years both in silviculture and agriculture.
That heavier and larger seeds furnish a better germination per cent. than light ones has been recognized for a long time by European silviculturists. The physiology of germination indi- cates that large seeds should succeed better, and repeated ex- periments by Bihler, Friedrich, Haack, Eisenmenger, and others establish this beyond much doubt. In fact forestry practice throughout Europe and especially in Prussia shows that smaller seeds produce fewer plants per hectare than larger ones in broad- cast sowing. Favorable and unfavorable site and season condi- tions produce far less variation in the final results in cases where heavy seeds are sowed.
In 1904 Blumer (22) conducted at the seed laboratory of the United States Department of Agriculture a series of tests upon certain American species of tree seeds. Pinus ponderosa from the Rocky Mountains and Pinus divaricata showed the highest germination but Pinus ponderosa from Oregon germinated ex- ceedingly slowly, a feature which also characterized Pseudotsuga taxifolia from the Pacific Coast. He noted great variation in the number of seeds per pound for the same species, especially
72 Richard EH. Boerker
for Pinus ponderosa. In the case of this species the difference was often as much as 100 per cent.; usually the difference in other specie$ did not exceed 50 per cent. Schotte (23), of the Swedish Forest Experiment Station, has shown that the size of the seed and the size of the cones decrease with increasing age of the tree in the case of Scotch pine. The work (24) done on seeds by certain forest experiment stations in Europe in 1907 with spruce showed that seeds from large cones germinate carlier than those from small cones; that the largest cones produce the largest and heaviest seeds and hence the largest plants; and that the effect of the size of seed upon the life of the plant has been noticed only in the first two years of its growth.
In Busse’s (25) experiments pine seeds were graded by means of a Kayser centrifuge into three grades according to weight. The heaviest seed made up 68 per cent. of the stock seed, the medium weight seed 27 per cent. and the light seed 5 per cent. He recommended the first grade for field sowing but said that the third grade should not be used. Sprout tests did not show any differences in germination results. Centgraf (26) examined 247 tests of pine seed as to the relation of the weight of 1,000 grains to their germination. He failed to find a relation between weight and germinative energy or germination per cent. In fact he found that the heavier seed averaged a smaJler germination per cent. than the light ones. He concluded that the slower germina- tion of big sced is probably due to a thicker seed coat of the heavier seed which determines in part its weight and which takes up water more slowly than thin coats of light seed. Some of these results do not agree with the many experiments made by foresters in Europe. These tests being made for commercial purposes cannot therefore be taken as conclusive.
While the size and weight of seed has been recognized as a factor in germination it also has been recognized as a factor in the early development of the seedling as has been indicated in a few instances above. One finds statements in regard to this rela- tion quite common in silvicultural works but very little material to substantiate these opinions. The view held by many writers is - summarized very well by Schlich in his A/anual of Forestry
(27)
Germination of Forest Trees 73
In the case of one and the same species large, heavy seed are better than light ones. The former generally possess a greater power of germination and the resulting seedlings show a greater power of resistance against injurious external influences and a more vigorous development which in many species is due to the greater quantity of reserve food materials deposited in the seed. This superiority at the first start should not be underestimated because it is recognizable long after the seedling stage has been passed. In many cases the dominant trees grow out of the seed- lings which had the better start.
The relation of size and weight of seed to germination per cent. and later development has been worked out to a much greater degree of certainty in the case of agricultural and garden seeds than in the case of forest-tree seeds. These facts have already been quite firmly established in practice and already adopted as a criterion of seed values. There is no reason why weight of seed should not play as important a part in selecting forest tree seeds as well as agricultural and garden seeds in the future, as the source and germination per cent. of those seeds.
A considerable amount of work has been done by investigators upon cereals, regarding the comparative value of heavy and light seed used in planting. Most of the work has been done with wheat, oats, and barley and the preponderance of evidence is in favor of the large seed. The hypothesis upon which this work has been based was the fact that, since the weight and size of the seed determines largely the amount of food material immediately available for the plantlet at the time of germination, it is reason- able to assume that these factors might have some influence upon the life of the plant and even upon the final crop.
Early experiments by Hellriegel, Wollny, Marek, and others (28) were favorable to the view that seeds of greater size and weight generally give more vigorous plants than those smaller and lighter. Hellriegel was of the opinion that differences at maturity between the product of heavy and light seeds are in- tensified when the conditions are unfavorable. Hicks and Dabney (28) have made a test of the relative effects of weight upon vigor, using many kinds of seeds. In the case of radish, vetch, sweet pea, cane, Kafir corn, rye, and oats the total weight of the seedlings in each case favored the heavy seed. The differ- ences in germination per cent. of light and heavy seed was not
74 Richard H. Boerker
conclusive. Only in the case of the corn was there a sufficient difference to warrant a conclusion in favor of the heavy seed. From the results of these experiments it seems logical to conclude that in general more vigorous growth and consequently a better stand in the field is secured by employing only the heavier seed. The effect of the size and weight of seed on production has been with no other plant so extensively studied as in the case of the wheat. The majority of results seem to favor the view that large and heavy seed are preferable. Zavitz (28) showed that the yield in bushels per acre was in favor of the large plump seed.
Trabut (32) found in the case of tobacco seeds that it was possible to affect a separation into heavy and light sorts through the capacity of these two kinds respectively to sink and float in water. It was found that the heavy seed produced plants which were greener, more vigorous, and of larger size. The yield from plants from the heavy seed was almost double that of the yield from the light seed. Shamel (31) secured results similar to these. Careful comparative tests of the light and heavy seeds of tobacco have proved that the best developed and most vigorous plants are always produced from the large, heavy seed while the light seed produce small, irregular and undesirable plants. In an experiment with Cuban tobacco seed Shamel found the germination of heavy seeds almost perfect while less than five per cent. of the light seeds sprouted. The plants from the heavy seed grew more rapidly than those from the light seed and reached the proper size for transplanting seven to nine days earlier than the plants from the light seed.
In the case of cotton seed, comparative production tests of the value of the heavy seed over the usual farm product have been made by the U. S. Department of Agriculture (30). The yields in pounds on equal areas in South Carolina show the gain from the use of heavy seed in two different cases to be 10.9 per cent. and 8.25 per cent. respectively.
Bolley (29) selected large and small grains from the same heads of wheat and found that the large grains generally pro- duced the largest yields. Waldron (29) found that short wheat culms, shortheads, and those with a smaller number of grains
Germination of Forest Trees 75
bear on the whole grains of a greater weight. Walls (37), work- ing upon the size of the grain and the germ of corn, concludes that the heaviest grains do not necessarily have the best ger- minating qualities and that plants from the heaviest grains attain the greatest weight, other conditions being favorable. Concern- ing the size of the germ he finds that the germinating properties of the kernels containing different sizes of germs may be equal; that the largest, hardiest, and most vigorous plants come from the kernels with the large germs; and that the plants from the kernels with the largest germs withstand the drought best. He says in the selection of corn, in order to insure a good stand and a large yield none but the large germed kernels should be used.
Harris (33, 34, 35) working on the differential mortality with respect to seed weight of beans and peas secured similar results, though in a different way. In the case of peas about 1,000 seeds from each of ten early varieties were weighed and planted. In seven cases out of ten the total weights of the seeds which ger- minated was higher than the total weights of the seeds which did not germinate. Cummings (38) worked with numerous kinds of garden seeds. He quotes numerous investigators who worked on corn, oats, wheat, sugar beets, cotton, and beans and practically all the results show an increased yield through the use of large seeds. He himself worked with squash, pumpkin, lettuce, spinach, parsley, radishes, beans, garden peas, and sweet peas. Here too the results were almost without exception in favor of the large seeds. Not only were the resulting yields larger and heavier but in most cases the yield was earlier. In the case of the radishes the large seeds produced more uniform crops one week earlier than the small seeds. Sweet peas showed earlier blossoming, a larger total yield of blossoms and a larger number of blossoms of good quality. On the whole the permanent ad- vantages accruing from large seeds are a larger and greater number of leaves, flowers and fruits.
Present Investigations
Having on hand several climatic varieties each of Pinus pon- derosa and Pseudotsuga taxifolia, I was prepared to determine
76 Richard H. Bocrker
the effect of size upon germination per cent, for many varicties of the same specics. This study would also bring out some interesting relations between these varietics, as for example, cor- relating the size and weight of the seed with the site upon which the trees grew.
The largest and the smallest seeds were separated from the stock seed and counted, weighed, planted and carefully labelled. Of each variety of Pinus ponderosa 500 seeds were used except in the case of the California varieties. Due to the scant supply of these only 200 seeds of each of these were used. In the case of the Pseudotsuga taxifolia 200 seeds of each variety were used. \fter germination began counts were taken every other day. The tables below give the size of the seeds, weight of 500 seeds, the number of seeds per pound, the final germination per cent., and
Size AND Weight of Secd in RELATION TO GERMINATION PER CENT. Pinus ponderosa
! Total Final Per Cent Source or Variety sie | Sta: |“exee| Soak. | Ce | ier ' , Cent Seeds
South Dakota. ... 04s Small 3-5 | 10.065 22,530 50.6
Large 5-9 | 20.720 IT,000 53-6 3.0 Harney, N. Fi, 3. De 2.) Small 4-6 ; 10.845 20,900 25.0 Ae
Large 6-9 | 20.720 II,000 | 40.2 15 Bitterroot, N. F., Mon. Small 5-8 19.050 I1I,900 7.6 led
Large 8-II | 30.400 7,450 8.0 Ud Weiser, N. F., Idaho...}| Small 4-7 17.100 13,250 60.0 ee
Large 7-10 | 29.540 7,650 84.8 24.8 Pecos, N. F., N. M....| Small 4-7 16.150 14,000 65.2 pees
Large 7-9 23.470 9,650 73h 8.2 California....... cacea| Stall J-II 35.500 6,350 63.5 nse
Large | 11-14] 67.000 3,385 7325 10.0 PPO POU stake go ae gine Small y-10}; 26000" 8,725 8.0 | bis
Large |10-14' 77.600 2,900 84.0 76.0
Pseudotsuga taxifolia
Caribou, N.F., Idaho. .; Small Bs 6.040 | | 32.5
Large on 8.290 | ed | ao.5 | 10.0 Pecos, N.F.,N.M.....; Small me 5.450 , | 65.0)...
Large... 7.850 69.0 | 4.0 Washington.......... Small, .. 3-780 16.5 |
Large sey 6.450 . , 16.0 | —0.5 ColOradGie ric: on exes aaie Small i... 3:750° | -xex. ~“boqor0' | shes
Large... 6.980 | ... . 88.0 | 9.0 Madison, N.F.,Mon...| Small | .. a:350) | ee | 43.5 Ries
Large eee 6.630 tee | Soca | 6.5
Germination of Forest Trees 77
the per cent. in favor of the large seeds. In converting grams to pounds it was assumed that 453.6 grams equals one pound. The germination period for Pinus ponderosa was 120 days and for Pseudotsuga taxifolia 100 days.
From these tables it will be seen that in every variety of Pinus ponderosa the final germination per cent. is in favor of the large seeds. In the case of Pseudotsuga tarifolia every variety except one shows a final per cent. in favor of the large seeds.
It is well known that there are defini imatic differences between the Rocky Mountains and the Pacific coast. The most conspicuous proof of this is in the flora of these regions. In general the Pacific coast is inhabited by relatively mesophilous vegetation, especially near the coast, while the vegetation of the Rocky Mountains is more xerophilous in nature. Again, the Rockies themselves show marked differences in this very respect in travelling from south to north and from east to west.
Probably the best way of studying the effect of great climatic vartations upon vegetation is to use polydemic species such as we are considering here. Pinus ponderosa and Pscudotsuga taxi- folia are conspicuous examples of this class of species. It is well known that both these species reach a better development on the Pacific coast than in the Rocky Mountains. It is likewise well known that they reach a far better development in the northern Rockies than in the southern. As a proof of this we have but to go to volume tables of these species in the I!”oods- man’s Handbook by Graves and Ziegler. In the case of Pinus ponderosa three tables are given, one for the Black Hills, one for Arizona, and one for California and Montana. In studying these tables it will be seen that the maximum heights and maximu i rs_an d maximum. heights_for a given diameter increase steadily in going from the Black Hills to California. In the case of the Deuglas Br the Game thing is true in considering the volume table for Idaho and Wyoming and that for Washington and Oregon. In the order of their
favorability for tree growth, as manifested by these species these regions arrange themselves in the following order, the least favor-
able being given first :
78 Richard H. Boerker
Black Hills
Arizona and New Mexico
Colorado and Wyoming
Idaho and Montana
Washington, Oregon, and California.
It is a striking fact in the case of Pinus ponderosa that the size and weight of the seed and their manner of germination follow exactly this same order. The smallest seeds come from the Black Hills and New Mexico and the largest from California ; the total weight of 500 seeds is least in the case of the Black Hills variety and greatest in the California variety, hence the number of seeds per pound is greatest in the former and smallest in the latter variety. Furthermore, germination begins sooner, the germination period is shorter and the germination curve rises more rapidly in the case of the South Dakota and New Mexico variety than in the case of the Pacific coast variety. Some of these striking relations between seeds and site are also shown by Pseudotsuga taxifolia. This species shows all these relations except those of weight of seed and number of seeds per pound. There seems to be no definite relation in this respect.
On page 79 the germination curves of the climatic varieties of Pinus ponderosa and Pseudotsuga tavifolia are given and they illustrate very forcibly what has been said above concerning the behavior of these curves.
In order to determine the effect of the size of the seed upon the size of the seedling shortly after germination, the seedlings were dug up very carefully as they were counted and taken to the laboratory and measured. The total length of the hypocotyl and tap root was taken in each case, the seed being excluded from the measurement. These measurements were kept separate for the small and large seeds and the results are given below:
Pinus ponderosa (Idaho)—Age, 2 Days 200 seedlings from small seeds averaged ............... 3.07 cm. 200 seedlings from large seeds averaged ............... 3.90 cm.
These 400 seedlings were classified according to their total length as follows:
79
Germination of Forest Trees
Tue Errect or Climatic Varietics UPON GERMINATION
The germination curves of Pinus ponderosa.
Fie. 2.
ey” t ee Te t saat t t! SCMRCESE (NEEggeeE n rite HO et HY a i eeidosstat EE: | s coon dened feaeeea geet i i rt jee a = sai We — FreiteteiHRn: = Farad Ht AH & cy HS 3 2 § = 4 as °° aaa SeERRee ac) Ho aS (at booal ry aa n ee uv > 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.. <nccncuansiarookoractncass 200 200
It will be seen that most of the plants from the small seeds fall between the limits 0.6 and 5.0 while most of the plants from the large seeds fall between the limits 1.6 and 6.0. In other words a greater per cent. of small plants were found among the plants that germinated from the small seeds. The average difference in size of 200 plants of each kind was 0.84 cm. in favor of the plants from the large seeds.
The measurements taken for another climatic variety of Pinus ponderosa were as follows:
Pinus pondcrosa (South Dakota)—Age, 4 Days
35 seedlings from small seeds averaged ............00005 4.6 cm. 51 seedlings from large seeds averaged .................. 5.6 cm.
Here there is a difference of 1.0 cm. in favor of the seedlings from the large seeds.
Similar measurements were taken in the case of Pseudotsuga taxifolia:
1 1
Pseudotsuga taxifolia (New Mexico)—Age, 4 Days 100 seedlings from small seeds averaged ................ 3.58 cm. 100 seedlings from large seeds averaged ................ 4.27 cm.
Germination of Forest Trees 81
These 200 seedlings were classified according to their total length as follows:
Seedlings from Seeds
Size, Cm, Small Large WHOIS sete ack antec doneealaeelaindddaduats 0 to) OLOATEO oan bleach beesanpne a Mee DEAR oO oO TISIG, - giv cvoncnmncraneenatadaannants I oO TIOS2iO! + sani ie oct amaee ts ehaaua ones 9 3 BIOS cui nes temas 4s A 9 BOBO nasddesss ween earecrs s 20 8 BOTERUG eect tisuas is esrn ean aemieaaeas 19 074 BIO AO: iaseisidnaien cis toard scutes moe naan 12 12 BDA ALS seceetcnasicbr css eesee whens banengenicataninrs 10 IZ AOZO cnewiatcassh veers as II 12 GHSSlS) wacxennedwner cer weraeaeaes 5 II GOROO oeshaccs hn ohaiciuhas eacenses 5 a OTA ~ ranesidatuale Sad 8.455 ditativatnseanne I 6 OIG 2770! scncansnoaincasien a wena rman antes (a) 2 TARTS: aia cicteennhen nee aek mane cunats fe) I Total: execs coke ween. T00 100
It will be seen from this table that most of the seedlings from the small seeds fall between the limits 2.6-5.0 while most of the seedlings from the large seeds fall between the limits 3.1-5.5. Just as in the case of Pinus ponderosa above we see that the greater per cent. of small seedlings are found among the seedlings that germinated from small seeds. The average difference in size of 100 plants of each kind is 0.69 cm. in favor of the plants from large seeds.
The measurements taken for another climatic variety of Pseu- dotsuga taxifolia were as follows:
Pseudotsuga taxifolia (Colorado)—Age, 4 Days
31 seedlings from small seeds averaged ...............4- 3-4 cm. 76 seedlings from large seeds averaged ..............04. 3.9 cm.
Here again there is a difference of 0.5 cm. in favor of the large seeds. In comparing Pseudotsuga taxifolia with Pinus ponderosa it is found that the size of the seed makes a greater difference in the case of the latter species than in the case of the former. Also,
82 Richard I!. Boerker
the difference in both cases is greater for the variety that comes from the drier climate, that is, the South Dakota variety of Pinus ponderosa shows a greater difference than the Idaho variety and the New Mexico variety of Pseudotsuga taxifolia shows a greater difference than the Colorado. The data here presented upon this phase of the problem, however, are not sufficient to warrant conclusions.
GENERAL SUMMARY AND CONCLUSIONS
I. The Effect of Habitat Factors upon Germination
— 1. Shade decreases cvaporation and transpiration and thereby increases the Soil-moisture content of the superficial soil layers. This increase in soil moisture content is best shown by the ac- companying diagram. This conclusion agrees with the results obtained by Stewart and Hasselbring who grew tobacco in shade tents.
2. Shade accelerates geriination, that is seeds germinate sooner in the shade than in the light. This acceleration is die to the increase in soil-moisture content spoken about above.
%
20 , | oO
Ope medrun? dese light Shade shade
Diagram showing soil moisture content in the three light cultures.
Germination of Forest Trees 83
Burns reached the conclusion that shade reduces the temperature of the soil and delays germination. Evidently there is a delicate balance between soil moisture and soil temperature, so that a slight deficiency in either might delay the germination process. In Burns’s case the temperature of the soil was so low, that in spite of the fact that there was sufficient soil moisture, germina- tion was delayed. In the present investigations soil temperature was kept at an optimum and measured differences in soil moisture were sufficient to result in an acceleration of germination in the shade cultures. One unfortunate fact about Burns’s work was that he failed to take into account soil moisture. In his experi- ments it must be assumed that there was sufficient soil moisture for germination. But there is nothing in his report which does not indicate that there was too much soil moisture. The recip- rocal relation between soil temperature and soil moisture is well known. Furthermore there is an intimate relation between soil moisture and soil aeration and germination. Such factors as these were evidently not taken into account to explain the delay in germination in the experiments cited.
3. Shade increascs the length of the germination perioc. This bears out to a certain extent Pittauer’s experiments which showed that germination proceeds more rapidly in the light than in the shade.
4. The germination curve of seeds sown in the shade rises more rapidly than the curve of seeds sown in the light. This con- clusion does not agree with the results obtained by Pittauer.
5. The final germination per cent. is usually higher in the case of seeds sown in the shade than those sown in the light. This conclusion, based upon abundant evidence, is not in accord with some work done by Atterberg which showed a greater germina- tion per cent. in the presence of light than in the absence of it.
—- 6. Light plays absolutely no part in the geritination of tree seeds; in fact shade has been found to be exceedingly beneficial to germination, other factors being equal. In the work carried on by Burns already referred to, there are at least two state- ments that a certain amount of light is necessary for satisfactory germination. Whether he means to imply by the term “ light”
84 Richard EH. Boerker
merely the luminous energy or the heat energy of the sun or both is difficult to say. Asa general thing it is impossible to have light energy without a certain amount of heat energy, but heat and light affect plants so differently that the final cffect of these factors is easily recognized. It is important to keep these two concepts separate in order to avoid confusion. Graves also makes the statement that light is necessary for the germination of Western White pine. It is inconceivable how luminous energy can play any part in germination, especially when the seeds are below the ground; it is likewise difficult to conceive what possible effect light could have if it did reach the seed.
7. An inadequate supply of soil moisture delays germination.
8. .\n inadequate supply of soil moisture decreases the length of the germination period.
g. A lack of soil moisture decreases the final germination per cent.
10. The germination curves of seeds sown in wet soil rises much more rapidly than that of seeds sown in dry soil.
11. Xerophilous species begin germination first, xero-meso- philous germinate Jater, and mesophilous germinate last.
12. The germination period of xerophilous species is shorter than that for either the xero-mesophilous or the mesophilous species.
13. In xerophilous species germination is accelerated in the gravel and sand; in mesophilous species it is accelerated in loam and sand. In general germination is accelerated in sand and gravel due not to the amount of soil moisture in these soils (see accompanying diagram) but to the amount of oxygen in the soil.
14. The germination period is longest in the sand.
15. The germination per cent. is usually highest in the sand.
16. The rise of the germination curve of seeds sown in sand is usually more rapid than of seeds sown in loam or gravel.
17. According to the table on page 29 of this report the volume of air space in a given volume of soil is about 39 per cent. for gravel, 33 per cent. for sand, and 53 per cent. for loam. In the accompanying diagram is shown the amount of capillary water in these soils at the time of watering and twenty-four hours later,
«
Germination of Forest Trees 85
This diagram shows very strikingly the water retaining capacity of these three soils. Not only do sand and gravel hold less mois- ture at the time of watering but they lose a much greater per cent. of it in the course of twenty-four hours than does loam.
-
% Efe)
Z0
/O
ada
leant Sand gra ve/
Diagram showing: soil moisture per cent. at time of watering; soil moisture per cent. twenty-four hours later.
When we consider the amount of air space in these soils and the amount of soil moisture each retains, the fact that loam usually contains a great deal of moisture and very little air space and that gravel contains very little moisture and a great volume of air space is very strikingly shown.
86 Richard H. Boerker
II. The Effect of Habitat Factors upon Stem and Root Development
1. Pinus ponderosa and Pinus strobus show increased height growth with diminishing light intensity. This conclusion bears out the results secured by Nikolsky who worked with pine and spruce and Burns who worked with Pinus strobus. On the other hand Badoux showed that pines decrease their height growth with increasing shade; but these trees were grown to a height of about six feet while Nikolsky and Burns experimented with much smaller stock.
2. Robinia pseudacacia and Quercus rubra show a decrease in height growth with diminishing light intensity.
3. Pinus ponderosa shows a decrease in length of tap root and in total length of laterals with diminishing light intensity. These results again bear out the conclusions of Nikolsky and Burns.
4. Robinia pseudacacia and Quercus rubra show a decrease in length of tap root and total length of lateral roots with decreased light intensity.
5. Pinus ponderosa, Robinia pseudacacia, Pinus strobus, and Quercus rubra show increased height growth with an increase in soil depth.
6. Pinus ponderosa, Robinia pseudacacia, Pinus strobus, and Quercus rubra show an increase in length of tap root but a decreased development of lateral roots with increased depth of soil.
7. Pinus ponderosa, Robinia pseudacacia, and Pinus strobus show a decrease in height growth with a decrease in the soil moisture supply.
8. Pinus ponderosa shows an increase in length of tap root and an wicrease in total length of lateral roots with diminishing soil moisture content.
9. Robinia shows a decrease in length of tap root with a de- crease in soil moisture supply.
10. Pinus ponderosa shows the greatest height growth in the loam and gravel, but Pinus strobus shows the greatest height growth in the sand.
it. Robinia psendacacia and Quercus rubra show the greatest
Germination of Forest Trees 87
height growth in the loam and the least in the gravel. Compar- ing this conclusion with No. 10 it is interesting to see that the conifers do well in either sand, loam or gravel, but that the hard- woods do best in loam only.
12. Pinus ponderosa, and Quercus rubra show the greatest length of tap root and greatest length of lateral roots in the gravel and the shortest length in the loam; Robinia pscudacacia shows the greatest length of tap root in the sand and least in the loam. In other words, root development is usually greatest in the gravel, and least in the loam. This conclusion agrees in part with Tolsky’s results that pine in black soils develop vertical roots but in sand develop a greater spread of lateral roots.
13. As far as height growth goes it is evident that pines, on account of their greater drought resistance, may grow as well in sand or gravel, or even attain a greater height in sand or gravel than in loam; while hardwoods which prefer moister soils grow best in loam. That root development is greatest in gravel is due undoubtedly to the fact that water quickly percolates through this soil and hence the roots have to go deep for the moisture. Reference to the diagram on page 85 will bring out these rela- tions more clearly.
Ill. The Relation of Size and IVcight of Seed to Germination and Early Development.
.
1. Large seeds of Pinus ponderosa and Pscudotsuga taxifolia produce a higher final gerinination per cent. than small seeds. This conclusion contradicts the results of Busse and Centgraf who found no relation between size of seeds and germination per cent., but it proves the contentions of many old silviculturists that large seeds produce a higher germination per cent.
2. At the age of from 2 to 4 days large seeds of Pinus pon- derosa and Pseudotsuga tavifolia produce larger seedlings than small seeds. This conclusion proves at least in part Schlich’s statement on page 73 concerning the use of large seeds in plant- ing and nursery work and bears out the contentions of practicing foresters in Europe that large seeds should be used in field sowing. This conclusion likewise agrees with the mass of evi- dence collected in connection with many cereal and garden vege-
88 Richard H. Boerker
table seeds, namely that the use of large seeds results in a better all round later development and a greater final crop.
3. The Rocky Mountain varieties of Pinus ponderosa produce smaller seeds, their germination begins carlier, their germination period is shorter, and their germination curves rise much more rapidly than in the case of the Pacific coast varieties of this species.
4. Except for the size of the seed, the same relations hold for the Rocky Mountain and Pacific coast varieties of Pseudotsuga taxifolia. Blumer noted the slow germination of Pinus pon- derosa and Pseudotsuga taxifolia from the coast and he also noted the great difference in size of the seed of Pinus ponderosa. These observations are corroborated.
BIBLIOGRAPHY
1. Clements, F. E. Research Methods in Ecology, Lincoln, 190s.
2. Zon, R., and Graves, H. S. Light in Relation to Tree Growth. U. S. Dept. of Agriculture, Forest Service, Bul. 92, 1911.
3. Hasselbring, H. The Effect of Shading on the Transpiration and Assimilation of the Tobacco Plant in Cuba. Bot. Gaz., 57, 1914.
4. Stewart, J. B. Effects of Shading on Soil Conditions. U. S. Dept. Agric., Bureau of Soils, Bul. 39, 1907.
5. Haak, J. Die Priifung des Kiefersamens. Zeitschrift fiir Forst- und Jagd-wesen, April, May, 1912.
6. Pittauer, E. Uber den Einfluss verschiedner Belichtung und Extremen Temperaturen auf den Verlauf der Keimung forstlichen Saatgutes. Centralblatt fiir das gesammte Forstwesen, April, May, 1912.
7. Graves, H. S. The Place of Forestry among Natural Sciences. Sci- ence; N.S: XEL.: 117, 1915,
8. Tolsky, A. P. Work of the Forest Experiment Stations of Russia. Review in Forestry Quarterly, III, 1905.
9. Burns, G. P. Studies in Tolerance of New England Forest Trees. Vt. Agric. Exp. Sta. Bul. 178, 1914.
10. Haberlandt, G. Physiological Plant Anatomy. English edition trans- lated from fourth German edition, 1914.
11. Coulter, J. M., and Barnes, C. R., and Cowles, H. C. A Textbook of Botany, IgIt.
12. Clements, F. E. Plant Physiology and Ecology. New York, 1907.
13. Timiriazeff, T. A. The Life of the Plant, ro12.
14. Shull, C. A. The Oxygen Minimum and the Germination of Xan- thium Seeds. Bot. Gaz., 52, 1911.
15. Shull, C. A. Semipermeability of Seed Coats. Bot. Gaz., 56, 1913.
16. Davis, W. E., and Rose, R. C. The Effect of External Conditions
Germination of Forest Trees 89
upon the After-ripening of the Seeds of Crataegus mollis. Bot. Gaz., 54, 1912,
. Eckerson, S. A Physiological and Chemical Study of After-ripening.
Bot. Gaz., 55, 1913.
. Shull, C. A. The Réle of Oxygen in Germination. Bot. Gaz., 57,
1914.
. Atwood, W. M. A Physiological Study of the Germination of Avena
fatua. Bot. Gaz., 57, 1914.
. Crocker, W., and Davis, W. E. Delayed Germination in Alisma plan-
tago. Bot. Gaz., 58, 1914.
. Crocker, W. The Role of Seed Coats in Delayed Germination. Bot.
Gaz., 42, 1906.
. Amerikanische Versuche mit Kiefersamen. Zeitschrift fiir Forst- und
Jagd-wesen, April, 1908.
. Schotte, G. Work of the Swedish Forest Experiment Station. Re-
view in Forestry Quarterly, IV.: 51, 1¢06.
. Die Zuchtwahl im Forstbetriebe und die Bestandespflege. Allg. Forst-
und Jagd-zeitung, December, 1907.
. Busse, J. Ein Weg zur verbesserung unseres Kiefernsaatgutes. Zeit.
schrift fiir Forst- und Jagd-wesen, May, 1913.
. Centgraf, A. Uber Beziehungen zwischen Tausendkorngewicht und
Keimenergy bei Kiefersamen. Allg. Forst- und Jagd-zeitung, June, 1913.
. Schlich, W. A Manual of Forestry. Vol. II, London, 18o1. . Duggar, B. M. Plant Physiology. New York, tort. . Waldron, L. R. A Suggestion Regarding Heavy and Light Seed
Grains. Am. Nat., 44, IgI0.
. Webber, H. J., and Boykin, E. B. The Advantages of Planting Heavy
Cotton Seed. U.S. Dept. Agric., Farm Bul. 285, 1907.
. Shamel, A. D. The Improvement of Tobacco by Breeding and Selec-
tion. U.S. Dept. Agric. Yearbook, 1904.
. Trabut, L. Bulletin 17, Service Botanique de 1’Algerie. Directeur
du Service Botanique, Governement de 1’Algerie.
. Harris, J. A. On Differential Mortality with Respect to Seed Weight
Occurring in Field Cultures of Phaseolus vulgaris. Am. Nat., 46, 1912.
. Harris, J. A. Supplementary Studies in the Differential Mortality
with Respect to Seed Weight in Germinating Garden Beans. Am. Nat., 47, 1913.
. Harris, J. A. On Differential Mortality with Respect to Seed Weight
Occurring in Field Cultures of Pisum sativum. Am. Nat., 48, 1914.
. Nobbe, F. Handbuch der Samenkunde. 1876. . Walls, E. P. The Influence of the Size of the Grain and the Germ of
Corn upon the Plant. Bul. 106, Md. Agric. Exp. Sta., 1905.
. Cummings, M. B. Large Seed a Factor in Plant Production. Bul. Vt.
Agric. Exp. Sta., 177, 1914.
PLATE |
Fic. 1. View of the interior of the greenhouse, showing cultures and hydrothermograph.
Fic. 2. View of the interior of the greenhouse, showing cultures and the cheesecloth tent used for the dense shade experiments.
PLATE Il
Tue Errect or Light upon Earty DEVELOPMENT
Fic. 1. The effect of light upon the development of Pinus ponderosa (S.D.). Ten plants each (1) grown in open light, (2) grown in medium shade. % natural size.
2. 3
Fic. 2. The effect of liyit upon the development of Robinia pseudacacia. Three plants each (1) grown in open light, (2) in medium shade, (3) in dense shade. 3% natural size.
Tue Errecr or Soil Depth upon Earty DrveLopMENT
Fic. 1. The effect of soil depth upon the development of Minus pon- derosa (S. D.). Ten plants grown (1) in deep, (2) in medium, and (3) in shallow soil. ™% natural size.
Fic. 2. The effect of soil depth upon the development of Robinia pseu- dacacia. Three plants each (1) grown in shallow, (2) in medium, (3) 10 deep soil. 1; natural size. —_
Missing Page
PLATE V
Tue Errect or Soil Texture upon Earty DEVELOPMENT
Fic. 1. The effect of soil texture upon the development of P/nus pon- derosa (S. D.). Ten plants each (1) grown in loam, (2) grown in sand, (3) grown in gravel. % natural size.
po ¥
1 we
3
Fic. 2. The effect of soil texture upon the development of Robinia pseu- dacacia, Three plants each (1) grown in loam, (2) grown in sand, (3) in gravel. ¥ natural size.
VITA
Richard Hans Boerker, born October 19, 1887, Brooklyn, N. Y.; prepared for college at Boys’ High School, Brooklyn, N. Y.; received A.B. degree from Dartmouth College, Hanover, N. H., in 1909; graduate student in forestry at the University of Mich- igan, IQO9-IQII, receiving the degree of M.S. in forestry in rgrt.
Engaged in private forestry work in New York and Michigan at various times; forester in the United States Forest Service in Colorado in 1910, and in California from 1911-1914 engaged in forest reconnaissance, silvical, and silvicultural work.
Graduate student in botany and silvics and Fellow in Botany at the University of Nebraska 1914-1915, receiving Ph.D. degree in 1915. Since 1915 in charge of a private forestry enterprise in New York State. .
Author of numerous articles on forestry subjects, 1907-1915; member of Sigma Xi; American Association for the Advance- ment of Science; American Forestry Association; Canadian Forestry Association; and the Ecological Society of America.
RicHarD H. BoERKER