G €€¥60L10 I9L1 & | ay 4 arial, md hae CARE OF TREES IN LAWN, SRE El VANDA €. 4 ‘eet ee ity. ing ina c Power spraying outfit operat American jPature Series Group IV. Working with Nature Via CARER OF TREES NSE AWN, STREET AND PARK WITH A LIST OF TREES AND SHRUBS FOR DECORATIVE USE BY BERNHARD E. FERNOW DEAN OF THE FACULTY OF FORESTRY, UNIVERSITY OF TORONTO ILLUSTRATED TTY NI Ee Y} \ NEW YORK HENRY HOLT AND COMPANY 1910 COPYRIGHT, 1910 « BY HENRY HOLT AND COMPANY + Published, April, 1910. TO MY VENERABLE FRIEND Dr. WILLIAM SAUNDERS WHO HAS DEVOTED A LIFETIME IN ADVANCING KNOWLEDGE OF TREE GROWTH IN CANADA, BOTH IN ITS USEFUL AND ORNAMENTAL ALSIP iC aS PREFACE THIS volume is an accident, as it were, so far as its authorship goes. The author being a forester by profession, and, therefore, concerned with the utilitarian use of trees rather than with their ornamental employment, the subject- matter of this volume might be considered foreign to his training. A forester, however, must be familiar with tree life in all its phases, so as to have judgment regarding the requirements of trees in health and disease and the proper care of them under all circumstances. Nevertheless, it was only an accident that induced the writer to devote time to the compilation of the present volume. A request by a tree owner for expert advice in the care of his lawn trees dis- closed the fact that apparently no satisfactory, compre- hensive treatment of the subject for amateur planters of trees was in existence, whatever might be said of the liter- ature for specialists. This induced the writer to attempt to set down, as briefly as possible, what every tree owner should know of the care of trees. The fact that the writer had for many years lived in Washington, D. C., and had taken a special interest in studying the composition of its many parks — indeed being for some time in charge of Soldiers’ Home Park, also acting on a commission on the reconstruction of Central Park, New York — these experiences with ornamental tree-growth may entitle him to claim the necessary judgment in selecting from the vast amount of information that exists on this Vii Vill Preface subject, that which would be most useful to those readers for whom the book is intended, namely, the practical lovers and owners of trees. Special acknowledgment is due to Dr. N. L. Britton under whose supervision the drawings of exotic tree species —and only such have been illustrated — were made. It is due to him to explain, that in the captions under these illustrations, contrary to the usage of Dr. Britton and many other botanists, species names derived from patro- nymics have been capitalized to conform with the mode of notation applied in the text, which is the mode still in use in most nurserymen’s catalogues. The author acknowledges his indebtedness to a large number of publications, too many to cite, from which he has extracted information, especially the many bulletins of Experiment Stations on combating insects and fungi. He claims originality mainly in the manner of presentation, and hopes that he has performed a useful service. Boke Toronto, March, 1910. CONTENTS CHAPTER PAGE een ERO DUCTORY, == - 5. a oe ae I Pe eHARACHERISMIES: STRUCTURE AND LIFE OF TREES 5 SPRUGIURE = 2-5 2= SA eset eae een Gene 6 GROWTH AND FORM Dey ELOPMENT 8 PHYSIOLOGICAL POINTS . . 17 E:COLOGICATEGROINTSE ya lee tae) eaten Te os en cy ots 2 RECUPERATIVE CAPACITY . . eS ea ee oe 26 Ill. DISEASE AND DEATH OF TREES. GENERALITIES 29 OLD eAGE 72 =. -- Ea ie en eae PO a ard 42°40) GENERAL CAUSE OF DRSSee TF Le cast ETA Leake ek cD KRUNGUSHIDISEASEStieY se 05 ays lky ee = asus, ce so SO INSECT DAMAGE . . Ve Bae Rl Mra ey ey ae 44 IV. DIAGNOSING DISEASES . aS ae Sn ee ea 51 INSECT DAMAGE . . SAE cio Ses, eC 53 FUNGUS AND BACTERIAL ‘Dismieas ye ee eee OL TSS Pea STOHOGICAT DISEASE Sas smn al anew eli eu asi 56 EFFECT OF SOIL CONDITIONS 57 ATMOSPHERICAL INEDUBNGES “- 5 = =. = = = = 63 OBNOXTOUSHGASES™ ssmeet ee ee Ss earl =) S-s 2) se 6 68 BERCERICNGURRENTS? se ben Sem i ta ee, eee ee 7/2 iLigisir (CONDON 2 = 5 os Gee 9s 68s ewe 3 MECHANICAL INJURIES . . 74 Vee CONTEROL, OF PHYSIOLOGICAL DISEASES AND TREATMENT OF MECHANICAL INJURIES.— GENE RAGS CARE OF VEREES = =) 92 = = So SOs PIMPROVEMENTDT= |) on 5, Sek eo 2 9 oc ees il FERTILIZING Ae 79 ROINTSEING (GRADING (4 << 2 . « CHAPTER Contents PRUNING, FOR) FORM y-ien ain ener ats PRUNING STREET TREES PRUNING FOR FLOWERS . REPAIRING DAMAGE 2 TREATMENT OF STREET ae CARE OF THE AGED . Quack MEDICINES VI. CONTROL OF PARASITES - FuNGuUS PARASITES INSECT PARASITES Civic COOPERATION GENERAL METHODS OF Spaces BITING INSECTS SUCKING INSECTS .- MECHANICAL OMee Ge OF fino BORERS AND BARK-BEETLES Root DESTROYERS SPECIFIC PESTS VII. CARE IN PLANTING TREES VIII. ESTHETIC FORESTRY “OR WOODLAND “PARK MANAGEMENT : ix CARE IN Lab Chol OF PLANT. MATERIAL BRIEF LIST OF BOOKS ON COGNATE SUBJECTS INDEX GENERAL CONSIDERATIONS .- List OF TREES DESIRABLE FOR SHADE AND Onis List OF SHRUBS SELECTED LISTS OF Prawe MEAeeran FOR Severe PURPOSES THE CARE OF TREES CHAPTER I INTRODUCTORY y HIS book is not a sentimental effusion on the Bey{| beauty and need of trees, but a compilation {| of information such as the owner of trees may be in search of. Throughout our entire continent, especially in its more settled parts, and most of all in its cities, there has never before been such widespread interest as is now manifested in trees and tree-planting for shade and ornament. Al- though this kind of tree-planting has been quite assiduously practised in past generations, and although as a result we are the heirs of stately elms and oaks and maples, the neces- sity of greater care for this inheritance has only of late been fully realized. As a consequence, the ‘Tree Warden” and “City Forester” have become recognized institutions, and the statutes of several states for the protection of planted trees bear testimony to the popular sentiment, and to the conception that the care of public shade trees is a public duty. Although with this awakened interest there has come forward a large amount of information regarding the care of trees, in the form of bulletins and essays, these generally confine themselves to some particular phase of the subject; a collective and more comprehensive manual, so far as the writer knows, is still lacking. It is to supply this gap that I 2 Introductory the present book has been written. Naturally the book does not bring much, if any, new knowledge; it is mainly a compilation of the well-known facts which bear upon the subject, selected, however, with the experience of a lifetime spent in the study of trees. Believing that only a knowledge of relationships, prin- ciples and reasons enables one to apply prescriptions intel- ligently, and that a knowledge of the nature of trees is necessary in order to care for them properly, it has been the endeavor to broaden in this direction, without, how- ever, becoming too technical. Technical language has been employed as little as possible and technical minutiz, which, though interesting and valuable, may in the ordinary routine be dispensed with, have been as much as possible avoided. The attempt to make the relationships clear to laymen has necessitated their presentation from various points of view in the different chapters, and this has led to repeti- tions; but, while such repetitions may be censured by the literary critic, the author believes that they serve the useful purpose of impressing the essentials upon the reader, and of making him familiar with the subject. The care of shade and ornamental trees is an entirely different matter from the care of forests. It is unfortunate that the distinction has not always been clearly perceived. The object of forestry is the substance of the tree: only when the tree is cut and its wood utilized, is the object of the forester attained: he grows trees, not to be preserved, but to be harvested. Hence to call the tree-wardens of towns and cities “foresters” is a misnomer. ‘The tree that satisfies the forester is most unsatisfactory to the landscape’ gardener or street tree planter, and vice versa. The latter arboriculturists are after shade or beauty of form, hence their treatment of trees is entirely different from that of the Introductory 3 forester, although, to secure the object in either case, the nature and life history of trees must be understood. On the other hand, no more fitting title, no better description of the duties of those who are set to care for our roadside trees or our city trees in street and park could be invented than that of “tree-warden,” a most expressive, dignified, and honorable designation. To the owner of trees who appreciates the value of his property and who realizes that it is an investment which can be duplicated only in time and by time, it is not neces- sary to point out that it is worth his while to take care of it. No millionaire can replace the ancient spreading oak or the shapely old elm in his lawn by any amount of expend- iture: these are the heirlooms of hundreds of years, and years alone can replace them. The Massachusetts courts adjudging the value of shade trees in damage as from $150 to $200 hardly come up to the full appreciation of their full worth. Even though it is possible to transplant full- grown old trees, it cannot be done with assurance of success, or at least not without interference with the natural form of the crown; in any case such transplants are a hazard. On the other hand, trees in place may be rendered almost imperishable by proper care and attention. To bring about this result requires some knowledge of the nature of trees, and also of the ills that may befall them. It is only through such knowledge that we are able to guard against the diseases and dangers which destroy prematurely so many valuable specimens on our lawns, and in our streets and parks. Many of the fine remnants of former forest glory or of old-time planting which adorn the grounds of our wealthy citizens and of our more humble home makers go to pieces, gradually, unobserved, and unnecessarily, because of neglect 4 Introductory and carelessness; a little care at the proper time would have saved the investment which cannot be duplicated in the owner’s lifetime. In almost every small and large town in the United States there has been a remarkable activity in the planting of street trees during the last fifty years; but for the lack of care the majority, perhaps, of these trees have become cripples, doomed sooner or later to an untimely death. The public usually recognizes only the foliage and the shade, and fails to observe the insidious work of fungi, induced through breakages and bad pruning, and over- looks the unsightly scars and wounds and stubs which bring about this premature decline and death —all for lack of care. To make owners of shade and ornamental trees more sensible to the care and attention which their property demands, to give them not only more interest but also spe- cific advice, a “first aid” toward a knowledge of what this care should be, and to assist tree-wardens in caring for their charges with more circumspection, this book is written. It is hoped that the perusal of these pages will enable any interested owner of trees to make himself intelligent as to the nature of trees, to help himself in most cases in their care, to avoid foolish practices advised by the quacks, and to superintend intelligently the execution of professional advice. For this purpose it is necessary first to have some knowledge of the life of trees and of. théir behavior in nor- mal conditions, for then only will it be possible to recognize abnormal conditions, to diagnose disease, and understand the rationale in the use of the remedies. — | It must, however, never be forgotten that the judgment of an experienced man is sometimes necessary to diagnose the case correctly, and to prescribe for it. CHAPTER II CHARACTERISTICS, STRUCTURE, AND’ LIFE OF TREES “| HE woody plants, trees, shrubs, and some vines, *4| differ from all other plants in at least two directions: namely, in their persistent life, with only temporary rest periods in growth, — a characteristic which indicates differences in structure from that of annuals —and in their elevation in height above the rest of vegetation, which implies, besides difference in structure, difference in performing the functions of life. Trees as a rule show these two characteristics of height and persistency of life in a most pronounced degree. In addi- tion, they differ from shrubs and vines by their form; namely, a single stem, rising from the ground, — the bole or trunk, —which develops more strongly than the branches, into which it divides in characteristic fashion, and which in their aggregate may be differentiated as the crown. ‘These char- acteristics of form, longevity, and height make trees the most prominent and one of the most important, and most interesting features in the living vegetable world. To be able to care for trees, to diagnose diseases or abnor- mal conditions and to apply remedies judiciously, it is neces- sary to know and understand something of the structure, and of the life requirements of a healthy tree in normal condition. Indeed, we may say that only to the extent that this primary knowledge is possessed, can a rational treatment of trees be expected. 5 6 Characteristics, Structure, Life of Trees Structure. That a tree, like every other living thing, is composed of tissues made up of minute cells varying in shape, size, and thickness of cell-wall, is probably well Co Be Me i | ——<—_ = Bia — es Ps Fic. 1. — Cell structure of a tree. (1) Appearance of a section of spruce wood, natural size; (2) Cell structure of same, magnified roo times (after Hartig, from Department of Agriculture, Forestry Division Bulletin, No. 10). known to everybody. But that the bulk of the bole of the tree is really not living but dead tissue, composed of cell cases without living contents, is perhaps less well known. While partially active in conducting water, most of the wood is merely supporting tissue. It is for this reason Cell Structure 7 that a tree may have its heart riddled and eaten out by fungi without losing in anything but firmness and stability. Cell Structure. ‘The living tissue of the bole lies on the outside of the wood, between bark and wood, —a narrow layer of a few cells, called the cambiwm, enveloping the dead wood. This layer, by division and growth of the cells forming it, makes the new wood of the year, the ‘annual ring,’ which again dies for the most part, soon after it is formed, only the outermost cell tissues, the cambium cells, remain fully alive, 7.e., capable of growth and subdivision.! Injury to this portion is, therefore, directly of consequence to the welfare of the tree. Besides the cambium layer, there are two other points at which persistently living cells are concentrated; namely, the tips of the roots or fibrils, and the tips of the shoots, the so-called growing points or buds. From the buds the shoots and leaves develop, the latter remaining living for only a few months, or, in the case of the needles of conif- erous trees, for a few years. It is, then, after all only one year’s product that really lives, in the full sense of the word, and this living por- tion encloses a mass of tissues which have lost their life, although they may be still of service to the tree in conducting and storing water or food, in giving stability, cr inother ways. The outer bark also dies, new bark being formed on the inside next the cambium; and, as the growth of the annual ring of wood and bark on the inside proceeds, the outer dead portions of bark must give way under the pressure of the interior growth. In most cases these dead portions of bark break in characteristic form into fissures, ridges, plates, or scales, which may sooner or later loosen and be sloughed off. ' This is not entirely true, for certain tissues like the pith rays may be still considered as living. 8 Characteristics, Structure, Life of Trees This thick or outer bark is, therefore, of no direct use in the life of the tree, though indirectly it may be of use in protecting the living tissue underneath against heat and cold, against drying out and against mechanical injury. The scraping of bark, so often foolishly practised, is, there- fore, in most cases either useless, or even, as it reduces the protection, injurious. Its only, yet doubtful, usefulness may be found in curtailing the chance for insects to hide their eggs or cocoons; and, under certain abnormal con- ditions, when the tree is “bark bound,” the operation of barking or slitting the bark may then be found useful in removing pressure, although other means of overcoming the trouble are probably better. Growth and Form Development. Except in the trees of the palm tribe (which do not increase much in diameter, but start from the seed in nearly full size of girth) the growth of the tree in thickness takes place by division and growth of the cambium cells, annually adding a cone-like envelope over the whole body of the previous years; in cross section these annual envelopes appear as “‘annual rings.” Hence the age of a tree can be determined from the number of rings, if it is cut low enough to include the first year’s growth. Only under rare conditions does the tree, in countries with a definite growing season, fail to make this annual growth, or does it make apparently two or more such rings. The growth in height or in length of branches and in the spreading of the crown is secured by addition of new shoots, which are developed from the buds. ‘These shoots grow in length only during the season in which they are formed, then become rigid, and in these, no more growth in length but only in thickness is experienced in subsequent seasons. The end-bud, which usually terminates the year’s shoot, if not lost by frost or drouth during the winter (and in some Fic. 2. — A tree, completely hollow at the base, but with the crown alive and fully developed. 10. Characteristics, Structure, Life of Trees species it is regularly so lost), or else a side-bud near the tip, resumes the activity in the next season and lengthens the id regular buds carbon dioxide I) summer K<€24 ry branch winter branch Z dormant bud Sound branch fi : . broken branch ZA stump decaying callused branch stub § water7> branchlets lost in early I <2 rool ca) P fibers conducting. em, eee Ah i ISIN: if nt Z a Lg Pater a minerals hearkroot. | WM ( Wil > tap-root Fic. 3. — Diagrammatic view of the various parts and functions of a tree. twig, forming at the same time the leaves, and possibly flowers. In this way, from season to season, story after story is built up: each twig, lengthening by additions and also gain- Growth and Form Development II ing in diameter by additions, grows into a branch; new branchlets start from buds along the length of the mother shoot, the daughter shoots forming side branches, and by repeated ramifications, gradu- ally from year to year, the crown is built up, character- istic in form and _ following well-known laws, typical for each species. One important fact to be ob- served in this process of build- ing up a crown is, that not all the buds which are formed on the twig develop into shoots; some remain undeveloped or dormant as buds, some are frozen, some dried up, some eaten or broken off; and even of the shoots which have been developed not all grow into limbs or branches: many are lost sooner or later by causes similar to those which destroy the buds, and by the with- drawal of light and food, as the upper portions of the crown develop and cut off from the less favorably placed portions the necessaries of life. Just as Fic. 4.— Bud Structure (Maple), A, longitudinal section through branch up; g, end bud; s, lateral buds; /, scars of leaves of last sea- son. B, cross section through bud, showing folded leaves in center and scales surrounding them. in the animal world the struggle for existence necessitates 12 Characteristics, Structure, Life of Trees violent death and diminution in numbers, more or less pro- portionate to food supply and new births, in order to keep an equilibrium, so in the forest a constant diminution of individuals takes place as the stand grows up and the indi- vidual trees expand, competing for the limited air space and root space. Fic. 4a.— Theoretical (B) and actual (A) development of buds. (From Department of Agriculture, Forestry for Farmers, after Miiller.) So also in the individual tree there exists a competition for light and water between the many buds, twigs, and branches, and sooner or later some must succumb as their number increases and the supplies become relatively less. As a result, in the full grown tree rarely more than eight or ten generations of branches can be counted, — the sur- vivals of this competition; the rest having been killed out, and being annually killed out, by the necessity of household Growth and Form Development 13 economy. If this were not so, if all the buds formed and all the branches developed in mathematical order, very different forms from those with which we are acquainted would result. This observation of the natural pruning of buds and twigs —withdrawal of water and light killing them and wind storms breaking them off — which takes place annually, especially as the trees grow older, is important in taking care of trees. It teaches that not all dying or dead branchlets, which we find on the normally developed tree, indicate any disease or abnormal condition. It teaches that pruning is not an unnatural but a necessary operation which, if neglected and not systematically directed by man, will be done by nature in a haphazard manner without ref- erence to the wishes of man as to form. We learn from this that with the expanding crown some parts, the less favorably lighted ones, as for instance the interior or the lowest portions in a conifer, must eventually be lost, and, if we remove them in time, we have it in our power to direct the development of the tree in form, favoring in the competition those parts, which we desire to preserve or develop. Another fact in the development of the crown, which from different points of view interests the forester perhaps more than the tree-warden is, that every regularly formed branch or limb has its origin, its base, in the F'.5-—Diagram showing the con- very center of the trunk or branch from nection of all which it arises, its pith or central portion Been wah being in direct connection with the pith of the bole or mother branch. The growth of wood which takes place annually on the bole or mother branch envelops 14 Characteristics, Structure, Life of Trees the base of the daughter branch more and more, while the latter itself is also growing in diameter. The forester is interested in this method of branch formation, be- cause he knows that, owing to it, every branch or limb which once existed will produce a “knot” in the lumber, although this lumber may be sawed from an apparently branchless bole. As long as the limb remained alive, this will be a “sound” knot; after the limb has died, it will be a “loose” knot (in conifers), or a decayed knot, leaving a blemish or hole in the board. The forester, there- fore, attempts to grow his trees so as to kill out most limbs as early as possible in order to reduce the size and number of knots and thus secure a branchless bole. ; When, however, a branch is Fic. 6.— Method of formation of a knot. Seven annual broken or cut off, a dormant bud layers of wood; a, b, basal é E : eee of a limb which lived may dev elop into a branch. Such four years, then died and dormant buds are connected with broke off near the stem. : : This leaves a “sound knot the pith bya ime trace of pithy, to the left of a, the branch pons F chub fo) tue aight faceenee a material not large enough to be “dead” knot soon to be cov- noted as an imperfection. ered by the growing stem. Th 2 : Ran i ee (From Department of Agri- ere 4S, ‘ail SIMLeErese® An wt 1S Names Forestry Bulletin, structural peculiarity which con- oO. IO). cerns the tree-warden. The center or pith of the branch or bole, which forms a direct and continuous communication through the entire tree from the Growth and Form Development 15 tips of the roots to the tips of the crown with all its ramification of branches, consists of very loose, thin-walled cell tissues; hence it affords an easy pathway for the growth of the mycelium of wood-destroying fungi. It is along this line of least resistance that the most rapid progress of rot is made, and hence there is need for particular attention to the branch wounds where the fungus enters. The root system develops in a manner somewhat similar to the crown, lengthening and ramifying by annual additions and increas- ing in diameter by division and growth of cambium cells. There are, however, differences in devel- opment, due, no doubt, to the difference of the medium in which yy. 7, — Method of formation the roots live. The soil offering of adventitious branches from ‘ ? the growth of dormant buds. more resistance than the air, the ramifications are less regular. Instead of having more or less systematically arranged buds from which new roots may form, irregular growing points may arise on any part of the root where the bark is not too resistant, thus pro- ducing the new growth. The root system is therefore less regular, less symmetrical than the crown system. Never- theless, as we recognize typical forms of crowns like that of the conical conifer, the spreading oak, the vase-shaped elm, so there are typical root systems, which fact has more bearing upon the form of ornamental and shade trees, than is usually recognized. Although the root systems of most trees are very adaptive, there is a limit to the adaptation, and, as the trees grow older, the difficulty of adaptation grows greater, and shows 16 Characteristics, Structure, Life of Trees itself in change of form of crown, or in lack of vigor. An entirely different shape from the expected may develop. There are three types of root systems: the tap-root, the heart-root, and the tracing-root; in some species the type is and remains very pronounced, in others a change and adaptation is more easily effected. The tap-root, perpendicular like the bole of a conifer and penetrating deep into the ground, is adapted to deep soils, and the difficulty of maintaining a hickory, a walnut, a fir, or some of the pines in a soil which is shallow — due to rocks or impenetrable layers, or groundwater close to the surface — is often due to the inability of adaptation of their tap-root systems. The oak, also a tap-root tree, adapts itself more readily than those mentioned, splits up its tap-root into several strong heart-roots, and develops a considerable quantity of surface or tracing-roots, but then the short, stubby stature and rapid tapering of the tree above ground shows that it is not in its natural condition. Elm, ash, and linden behave in a similar manner, hickory and walnut resent curtailment of their tap-root more strenuously, and hence are difficult to transplant or to grow on shallow soils. The spruce, on the other hand, is one of the trees, which, with a typical tracing- root system, developing horizontally in the upper soil strata, can occupy the shallow soils without effect on its form devel- opment. So can willows, poplars, and birches, while beech and maple with a regular heart-root system made up of several strong roots descending obliquely into the ground, stand between the two types first mentioned, both in require- ment for soil depth, and in adaptability. With the recognition of these characteristics in root development we shall not expect the same species of trees to produce the same form and remain alike under all Physiological Points 7 conditions. To this very important relation which exists between root and crown development we shall refer again further on. Instead of leaves, the youngest parts, 7.e., the tips of the roots, are beset with fine hairs; delicate structures which serve the purpose of taking up water. The root-hairs live only a very short time, hardly through the season, being ever replaced by new hairs near the tip, which constantly pushes into new soil. The tips of the roots, therefore, are the most important part of this organ for the life functions of the tree. Physiological Points. We may now take a brief glimpse into the household affairs of the tree, — the manner in which it lives. The essential fact which must be realized is, that the leaves and buds at one end, and the tips and youngest parts of the roots at the other end, with the cambium layer con- necting the two, are the living tissues, and hence the main factors in the household. The tips and youngest ends of the roots or rootlets, densely beset with little hairs, are the mechanism which takes up the water and minerals from the soil. These are conducted through the roots by way of the cambium and the younger wood and bark to the leaves. The leaves in turn take up carbonic acid from the air, decompose it in their green parts (chlorophyll) under the influence of light, and combine it with the minerals and water into food materials which can be used in building up the body of the tree. This process is called assimilation. The food materials, manufactured in the leaves, wander through the veins and stalks of the leaves into the cambium and the youngest wood and bark of the stem and root, where they are used in new growth during the season, making the annual ring, or else are stored (especially in the pith rays) 18 Characteristics, Structure, Life of Trees for next year’s growth all the way down to the root tips. The stored material is then used the following spring to form leaves and shoots and new rootlets. The whole mechanism of the tree can be compared to a sytsem of water works — water being the most important factor in the life of the plant — the root tips being the pumps or valves taking up water with minerals in solution from the soil. The roots and stem and branches are the conducting pipes; the leaves are the engines where the power is applied which sets the current in motion: namely, heat, light, wind, and other causes of transpiration (evaporation). In the leaves, which may also be regarded as the stomach of the plant, the raw food is digested and assimilated into a form in which it may be used by the plant, and thence it is carried by osmosis ' to places where it is needed. It stands to reason that the amount of foliage which is active under the influence of light, determines the amount of assimilated food material which will be at the disposal of the tree and hence the amount of growth. The leaves and their. healthy function are, therefore, of the highest im- portance to the tree; but just as important is the number of root tips capable of securing water and the necessary minerals. For best results the amount of active foliage and of active rootlets must be in direct proportion; and, indeed, there is such a close relation between the two, that if for some rea- son the normal amount of active leaf surface is reduced, as by insect injury, a corresponding amount of rootlets may die because not fed, unless a surplus of stored material is available. Even more surely, if the root system is in any way curtailed, as for instance when a cut for a street is made, 1 Osmosis is the name for the process by which liquids are diffused through membranes. Physiological Points 19 or the ground lowered, or if the roots fail to be supplied with sufficient water, the foliage and with it the whole crown will suffer in proportion. Generally speaking, each side of the crown is in more or less direct relation with the same side of the root system, the roots living on one side feeding the foliage on that side, and vice versa. There is, in other words, more or less direct reciprocity between branch and roots. Hence, if a root on one side of a tree is cut through, a branch on or near that side may die or suffer. As the shoots lengthen each year, so the roots lengthen; and since only the youngest root tips remain active in taking up water, it stands to reason that they must be fed in order to renew themselves, and to per- form their function. Anything that prevents the descent of food material from the leaves, as when by partial or total girdling ' of the tree the conducting tissue is reduced, will therefore starve and eventually kill the root system, partially or entirely. Con- versely, if the root cannot furnish enough water to the leaves, these must wither and die, and finally the whole tree will suc- cumb. Again, if any of the needed minerals are deficient in the soil, this fact will be indicated by at least some abnormal development in the foliage, changes of color, size, form, etc. The interdependence, then, of roots and leaves is complete, an important fact in diagnosing abnormal conditions of either. Normally, the leaves elaborate the food materials during the summer in sufficient quantity to supply all the material of the present year’s growth, and, in addition, also accumu- late a surplus, which wanders out of the leaves before their fall, and is stored in the wood to be used for next spring’s 1 Girdling is the cutting through the cambium layer, or taking off a ring of bark around a tree. < 20 Characteristics, Structure, Life of Trees growth of buds and foliage. Hence a deficiency in food elaboration or defoliation in one year may, according to the time when it occurs, influence the growth and health of that and the next year; or the unfavorable season of one year may not show its effects until the following season. Besides food, a tree, like an animal, needs air or oxygen for respiration. The importance of this fact is perhaps very imperfectly realized by the uninitiated. Yet not only the leaves but also the twigs, branches and bole, and even the roots have breathing pores in the developed fissures of the bark, for the purpose of conducting air into the interior. That the roots must breathe is often forgotten, as when trees are planted too deep, or when ground is filled in on top of them. Many a tree is lost by this ignorance. The more compact the soil and the deeper the cover, the surer and quicker the result; the tree dying from suffocation. The same result is induced by flooding, or even a very rainy sea- son may, on compact soil, so reduce the aération of the roots as to kill them. Trees growing in swamps have adapted themselves gradually to the difficulty of root respiration, and the ground around trees grown in such conditions may be filled up without the same detriment that would come to trees not so adapted. Whenever there is a change made in the surroundings, especially in soil and in light conditions, there must take place an adaptation of the root system to the change. The tree, however, can make this adaptation only gradually, hence any contemplated change in the environment must be made by degrees or else the tree will suffer. It appears from the brief description of the household economy of the tree, that the requisites for tree life are, like that of other plants, first of all, at the root: — Ecological Points 21 Water, available in such a way that it can be absorbed by the roots; this depending upon physical and chemical conditions of the soil. Minerais, of certain kinds, in available form but only in small quantities, such as are found in almost all soils. Air, for respiration. The amount required of these supplies varies with differ- ent species and with their gradual adaptation to existing conditions, also with the conditions at the other end, namely, the environment of the foliage. Here the indispensable air for respiration and carbon supply is almost invariably present, but in addition there dire required :—— Certain conditions of the air as regards temperature and humidity in order to produce the so-called transpiration, i.e., evaporation of water from the leaf surface. This pro- duces a stream of water flowing from the roots through the young wood, the carrier of minerals upward and of assim- ilated food materials downward as needed. In addition there is necessary: Light of certain intensity to produce the chemical action in the leaves by which the food materials are digested or assimilated. Ecological Points. This relation and adaptation of the plant to its surroundings has been called its ecology. Some of these conditions of environment are unalterable in any locality and situation; climate in general and the seasons being, of course, uncontrollable by man. The adaptation of species to given climates has been accomplished during ages in such a manner as to assign to them fields of distribution within which they are found by nature, 7.e., within which they can perform their life functions satisfactorily. This process of adaptation is 22 Characteristics, Structure, Life of Trees unquestionably still going on, species increasing their field of distribution, and also changing their functions to meet changes in climate, or else succumbing and dying out through inability to adapt themselves. But this is a matter of long-continued evolution and very gradual change, in which thousands of individuals succumb while a few selected ones are adapted. Artificial acclimatization, therefore, is probably not, at least practically, within the means of man, as far as the long-lived arborescent forms are concerned, whatever may be accomplished with annuals, or even with shrubs, which send out new shoots from the root-stock annually. But transfer from one locality to another where the tree is not native has been practised successfully, the assumption being that the climate of the new location was favorable to the exotic newcomer. Whether or not such transfer may be successfully made is in general a matter of trial, climate being too complicated a matter to permit ready comparison and prediction of the adaptation of the plant to its new surroundings. We have only a few points for basing a judgment as to the probability of success. It is, for instance, not likely that a tropical species or one of southern warm latitudes will, as a rule, adapt itself to a northern climate. Species from moist climates are apt to succumb in dry ones. The nearer in temperature and moisture the climate is to that of the native habitat, the greater the likeli- hood of success in transplanting a species. Cases are known when the new environment has proved even more favorable to the development of exotics than to that of its native flora, as in the case of European species in California and in other parts of this continent. On the other hand, while a species so transferred may be able to live in the new surroundings it may develop differently from its habit in its native country. Again, some species have 991} []e1 ® st ssauddd pleg ay], ‘EMR}G Ul Gnays B saUIOdaq Inq “YNOS 9y) UT apnyyry UloyJOU B O} ULaYyINOS B WoL, SuNuR[dsuRs] JO Waa sy, — °g “OT 23 24 Characteristics, Structure, Life of Trees such a wide range of distribution, through such a variety of climates, that the success depends upon the choice of the locality from which the plant has been derived or from which’ the seed has been secured, for the seed preserves all the characteristics of its mother plant. A case in point is the Douglas Fir, ranging from British Columbia to New Mex- ico. Plants of this species, when brought from the humid, mild Pacific Coast do not thrive in the drier, severer climate of the Eastern States; but if grown from seed collected in the dry Rockies, they will succeed. It must also be kept in mind that there is considerable variation of climate experienced locally within narrow limits, as for instance, in going from the foot to the top of a mountain, or with change of aspect, and with different exposure to winds. Hence the tree in one place may find satisfactory environment, when in close neighborhood, but in a different situation, it may not: the south side of a town is warmer, the northwest colder, but healthier, the southeast most equable, and so on. While, therefore, the fact that different species of trees are by nature adapted to certain climatic conditions must influence the choice of trees for planting in a given locality, and while the natural adaptation of species to deep or shallow, wet or dry soils is also a matter to be considered in the selection of plant material, we know that soils at least can be adapted to support any tree species and also that the light conditions can, to some extent, be made favorable to the needs of the species adapted to the climate. There is one condition of soil which is most favorable to all tree species, namely, a deep, moderately loose, sandy loam, which permits satisfactory aération and fur- nishes an even water supply. When we speak of trees adapted to other, drier or wetter, more compact or looser, Ecological Points 25 soils, we mean that they can still prosper under less favor- able conditions, if necessary; yet they would do best on the soil as described, which is, therefore, the nurseryman’s choice. As regards light supply to the foliage, we have, of course, no means of increasing or modifying it in general, yet in | group planting, park planting, street planting, and even in pruning, the knowledge that different species require differ- ent light intensity for their best development is essential; for here proper adaptation to light conditions, and artificial changes in light conditions can be practised. All trees thrive ultimately best in full enjoyment of light and then develop their characteristic form, as we see it in single trees on the lawn; but, if placed in close neighborhood of each other, the fact will soon appear that one species is “stronger” than another; that means the one spreads its branches and kills out those of its neighbor by its shade. In other words, the foliage of one species requires more light to perform its work than that of another. This fact is exhibited in the individual tree itself. The interior of the crown in those which need much light, like the birch or aspen, thins out, is empty of foliage, because of the shade which the exterior exercises; it loses its lower branches sooner on account of the shading by the upper, or else the lower reach out farther to escape suppression. On the other hand, the tolerant or shade-enduring kinds, like beech and sugar maple, are characterized by compact and dense crowns: their foliage even in the dark interior of the crown can perform its office. And so a relative scale can be made with reference to light requirements from the most light- needing to the most shade-enduring. Birch, aspen, willow, poplar, and pine are examples of those more sensitive to the withdrawal of light; beech, sugar maple, holly, spruce, 26 Characteristics, Structure, Life of Trees fir, and hemlock are examples of those which can endure considerable shade. The practical importance of this fact is exemplified in almost every park or yard where groups are planted, either by the failure of the designer to group trees with reference to their characteristics, or by failure of the manager to cor- rect in time such changes of relationship, and by allowing the “stronger” to damage or kill out the “weaker.” The knowledge that this strength or weakness is merely in the light requirements can be used, first, in restraining the stronger by proper pruning, if the two are to be kept together; second, if it becomes necessary to plant between existing groups, in choosing a species capable of bearing the shade of its neighbors; and finally, in pruning individuals of the light-needing kind so as to give more light to the interior of the crown, making it fuller and more compact by the development of dormant buds. Recuperative Capacity. There is one other feature in the economy of the tree, important to the tree-warden, by which it differs from the animal household (with exceptions), namely, its ability to replace lost parts. This is due to the fact that it produces and keeps alive many more buds or growing points than it can develop in a season. . As we have seen, only a few of the many buds formed each season grow into shoots and make leaves; the majority die, are killed by insects, or dry out, while a number remain living but undeveloped, keeping dormant until needed. Let a tree be defoliated again and again by insects in a single season and the dormant buds will replace the lost foliage as long as there are stored food materials at hand to feed them; let a twig or branch be cut off, and several dor- mant buds near the cut base will vie with each other to replace it; cut off the whole tree and with most deciduous- Recuperative Capacity 2 leaved trees the stump, if not too old, will have dormant buds still alive below the bark to force themselves through and make sprouts to replace the lost bole; or else the cam- bium layer may form new, so-called adventitious buds for the same purpose. Lost roots too can be replaced, if conditions are favorable, through adventitious buds, a fact of importance in trans- planting trees, when usually a part of the root system can- not be taken up, and must be replaced by the tree in its new position. Upon this observation of the replacement of lost parts the practice of pruning is based: the tree pruner, by lopping off branches and thereby changing conditions of nutrition, produces at will new branches, and influences direction, character, and amount of development. Tree surgery becomes, therefore, next to securing favor- able soil conditions, the most important factor in the care of trees, for it enables us to remove diseased, malformed, undesirable parts without fear of harm to remaining por- tions and with the possibility of restoring to symmetry and vigor a dilapidated and sickly tree ruin. With old age, to be sure, this capacity for replacement may be lost in the older parts, and it must also be kept in mind that different species are more or less vigorous in developing dormant buds. The essential points, then, of tree life to be kept in view faerie care of trees are: — 1. The living portion of the tree is found in the cam- bium layer directly under the bark and in the tips of branches (buds) and roots. 2. Root tips and foliage are in direct communication with each other and interdependent, relying on each other for food. 28 Characteristics, Structure, Life of Trees 3. Water, minerals, and air in sufficient quantity at the roots are the principal needs of trees, and especially the aération of the roots is of importance, while light in varying amounts is required by the foliage for proper function. 4. Trees have the capacity of replacing lost parts. CHAPTER III DISEASE AND DEATH OF TREES—GENERALI- TIES =YJOR normal development trees require, as we have ) seen, light, heat, water, air, and nutritive ele- ments in certain amounts. If any of these conditions or elements are temporarily deficient (or sometimes when in excess) the normal functions are interfered with, and the tree may be ailing, although not necessarily sick, for it may recover its normal condition as soon as the deficiency is corrected. We speak of disease only when live parts fail to perform their normal functions and begin to die before their time, that is to say, when buds, rootlets, or cambium die at any time, and leaves change color, become dry, and fall before the end of the season. Since, as we have seen, the living parts of the tree lying on its periphery rejuvenate themselves every year by the formation of new shoots, buds, cambium and rootlets, there can be actually no natural death from old age in the same sense as in animals. Even death from internal causes as a direct result of disease, at least sudden death, is rare. Trees die mostly as a result of unfavorable external con- ditions, which interfere with their nutrition, and which are generally capable of control. As a rule, they succumb so gradually that they actually die by inches; it may take many years before all life is gone, and hence there is time for recuperative measures. 29 30 Disease and Death of Trees — Generalities Often it is difficult even for the expert to determine the exact cause of final death. The cause frequently lies hid- den under ground, or is only to be discovered in a compli- cation of various conditions, operative at different times. Finally, however, it is mostly interference with normal nutrition and especially deficiency in water-supply that is the ultimate cause of death. Old Age. Since the truly living portion of the tree is annually renewed, it follows that when we speak of the length of the natural life of trees, we can mean only that period of time during which the tree without human aid may, as a rule, successfully resist unfavorable external influ- ences of soil, climate, or attacks of parasites, and may repair mechanical injuries. Although we do not know in trees the decline which characterizes the old age of animals, yet we find that, as in animals, extreme youth as well as extreme old age predis- poses the tree to diseases, and that serious consequences and fatal results are more apt to follow the attacks of enemies in the younger and in the older stages than in middle life. One reason for the greater danger to old trees seems to be in their mode of growth. Since trees lengthen their shoots as well as their roots by additions, the distance between the place of supply and of consumption of water constantly increases. Finally the forces at work can not readily pump the water against gravity and friction from the ever farther removed root tips to the utmost twigs in sufficient quantity to satisfy the demands of a drouthy season. The twigs die back again and again, and thus a limit to height growth is set. At least this is the theory of the writer, and no better one has as yet been presented. But there is also opportunity given for fungi to enter Old Age 31 through the dead twigs as well as through the larger branches, broken off by the winds; the danger of damage from wind, snow, and ice pressure increasing with the growth in length which adds to the leverage. Rot, riddling the bole (which is really dead matter) and eating out the heart of the giant, does not really kill, but after years of work the stability of the bole is undermined and eventually the tree succumbs to a windstorm; broken, it may be, in full leaf and, as far as the living parts are concerned, in full health. Just as wild animals are said to die mostly from violence, so trees in nature break down under the violence of windstorms rather more often than they succumb to natural death or disease. When this time of insufficiency of water-supply and hence 'endangered old age will arrive, depends on a variety of con- ditions. Difference in wood structure and hence in conduc- tivity for water may make long-lived and short-lived species; deep soil and ready water-supply for the roots and favorable climatic conditions, increase height growth, and may also possibly lengthen, or, as may be, shorten the life of the individual. Again, some species, or some varieties or even some individuals of a given species may be found to resist damage more readily than others, or else be more predisposed and liable to disease. Some are more adaptive to a change in the environment, while others quickly resent such changes, especially as regards water-supply at the roots or transpira- tion at the foliage. Diseases in trees are usually more or less localized, spread- ing gradually, and in the absence of a nervous system, sec- ondary complications in other organs, as they occur in the animal body, are not generally observable. One portion of the tree may remain perfectly normal and healthy while another portion may be diseased or even dead. 32 Disease and Death of Trees — Generalities Nevertheless, since different parts are interdependent for their nutrition, any interference in feeding arrangements will be more or less felt, at least in all growing parts which organically belong together. It is, therefore, usually, one side of the crown, in sympathy with the same side of the root system, which is diseased or dead, while the other side may remain alive and even vigorous. This fact, together with the ability of trees to replace lost parts, makes it possible to resuscitate and restore quite dilapidated specimens by surgery and proper treatment, and to prolong their life almost indefinitely. General Causes of Disease. ‘There are two general causes of disease, namely, unfavorable environment and parasitic organisms (which, however, should really be considered a part of the environment). Under the influence of these two we may group for diagnosis and treatment four classes of troubles to which trees are exposed, namely: physiolog- ical diseases which are produced by generally unfavorable conditions of growth in atmosphere, climate, or season, and soil; mechanical injuries, which destroy living parts or else weaken the dead wood of the body; attacks of fungi and other plants; and attacks of insects. Usually several of these causes work together or are even interdependent, and it is not always easy to tell which is the primary, which the secondary, cause of the diseased or abnor- mal condition. This difficulty of diagnosis is especially experienced when there are no visible signs of insect or fungus pests present and when the trouble seems not localized but exhibits itself in general debility or sickly appearance. Fungus attacks are usually secondary results of mechan- ical injuries, and insect pests become in most cases fatal only when other debilitating causes are at work simulta- neously. General Causes of Disease 33 Shade trees in city streets are especially subject to many adverse conditions, which make the attack of fungi and insects much more dangerous than it would be in the virgin forest. Injuries from gnawing horses, abrasions from passing vehicles and other agencies give entrance to fungi, reduce the feeding area and the vigor of the tree; pavements and macadamized roads reduce the water-supply and the supply of air to the roots; excavations for buildings, sewers, water-, gas-, and steam-pipes destroy parts of the root system; gradings do the same, and earth fillings change the water and air supply; gas leakage at the root and other obnoxious gases at the foliage interfere with the health and vigor; inattention to the wounds and broken limbs invite fungus attacks; and electric wires introduce the danger of electric discharges. All these untoward conditions of the environ- ment together with the mechanical injuries, if not fatal in themselves, tend to reduce the vigor of the tree and make it more susceptible to the attacks of parasites. The first concern of the tree doctor, therefore, is to secure a favorable environment, — sanitary surroundings for his charges, which will keep them in vigorous condition and enable them to fight off their enemies in the plant and animal world. The conditions in the atmosphere are only very partially controllable; drouthy and wet seasons and the ills of frost and lightning have to be endured without much, if any, chance of counteracting their unfavorable influences. But the medium in which the roots perform their function, the soil, is much more readily influenced, and here, therefore, lies the main activity for securing favorable conditions. As we shall see more fully later, the regulation of the water- supply to the roots and a sufficiency of air or oxygen for their respiration, and, to a minor degree, a satisfactory amount of available mineral material are the means of 34 Disease and Death of Trees — Generalities keeping trees in vigorous constitution and of avoiding physio- logical diseases. Not only are certain species adapted to certain climatic conditions and hence may not be transferred into a different locality with assurance of success, but even the individuals of the same species are adapted to the special features of their nearer surroundings of local climate as well as of soil, and resent change, or at least must re-adapt themselves if moved into new surroundings. To some extent, even the seed itself inherits this adaptation; hence the young plants of Pacific Coast conifers, grown from seed derived from the mild, moist climate of their habitat, may suffer from frost and drouth in the Eastern States, while plants of the same species, derived from the rigorous, dry, alpine climate of Colorado, will be hardy. In transplanted trees this difference in derivation of the plants and the difficulty of adaptation may sometimes account for their ailing condition, and may result in their death. The seasons will naturally influence the condition and disposition to disease of the tree: a period of drouth, for instance, may kill feeding roots, leaves and branches, and at the’same time open the door for fungi to enter; a period of wet, rainy and cloudy weather may have the same effect, by depriving roots and leaves of their respiration; a severe cold spell in the spring may kill foliage and twigs, and espe- cially “kill back” immature young wood of the previous season, such as forms when a moist fall follows a dry sum- mer. Attacks of fungi may or may not be of moment accord- ing to the season and the condition in which the tree is found by these parasites. . Mechanical injuries, by which the truly living parts are exposed to the air, are perhaps the most prolific cause of trouble and disease. -—A “sun-scalded” silver maple still b.— The bark torn off from one- alive, giving chance for fungus to enter. half of the bole. Immediate attention by tree wax and wrapping has kept the tree in full growth. 36 Disease and Death of Trees — Generalities A tough skin or epidermis protects the leaves and young shoots, and a corky bark the living portion of the older parts of the tree, and prevents, or at least impedes, access of insects and fungi to the tender living tissues. But there are innumerable opportunities of breaking through this protective cover and exposing the delicate tissues below. Minute punctures are made by insects; hailstones tear off portions of leaves, produce contusions on the young twigs and lacerate the bark; windstorms tear off foliage and twigs and break branches; frost and sun-scald split and kill portions of the bark, and lightning may rend the bole to the very heart. In addition, careless man and gnawing animals inflict wounds, small or large. The result is, first of all, an interference with the normal functions of the tree: certain areas of conducting tissue or, in the leaves, of assimilating tissue are destroyed, and by so much the equilibrium of the whole system is disturbed in its nutrition; and secondly, a way is opened for fungi to attack the living or supporting tissue. The recuperative power of trees is so great that almost any wound, if properly assisted, can be healed by the pro- cess of callusing, described on pages 91-98. All that the tree doctor can do, or needs to do, in most cases, is to see that this healing process is performed promptly and without interference. The sooner the injury is looked after the better, so that the secondary evils of fungus infection may be prevented. Fungus Diseases. Any portion of a tree which has been mechanically injured, so as to expose the living tissues of the wood, is subject to the attacks of fungi, although sometimes attacks may occur without such injury. There are fungi which live on trees as saprophytes, using the tree merely as a location; others which feed on the tree, Fungus Diseases: 37 sapping its life, ~ true parasites; others again are in some stages of development parasitic, and in other stages only saprophytic. There are fungi living on leaves, others living on the roots, others on the bark, and again others living on the wood of the tree, producing its decomposition, or what is commonly known as rot. The young plants or seedlings are exposed to a large num- ber of fungus enemies, which do not trouble them in later life, but we shall here only discuss those occurring in older trees. Of the many interesting phenomena in the life history of the fungi one of the most important is that many not only pass, like the insects, through different phases or forms of development, but in these different phases live on different “hosts,” as the plants are called on which they feed. The well-known rust of wheat lives in one phase of its development in the ground, as many others do, and in an- other on the barberry bush; some fungi, active on the juniper tree, are found in different stages of development on apple and other trees. A rust which attacks the needles of pines is dependent for its development on ragweed or groundsel (Senecio). Lately a new pest attacking our white pine has been introduced from Germany, and this passes one stage of its development on currant bushes. The presence of a certain plant may, therefore, be a cause of the spread of the disease on another, and the removal of the host plant as well as of the infected trees or parts of them is often the only means of getting rid of the trouble. In so far as specific enemies exist on given species, if an epidemic has set in, it may become practically necessary to replace the species by another in order to avoid the spread or renewal of the trouble. The fungi which attack the foliage usually destroy only 38 Disease and Death of Trees — Generalities portions of the leaf surface and thus simply reduce the assimilating area and lessen the feeding capacity of the tree; thereby the growth of the tree is diminished in proportion to the leaf area destroyed. Since the leaves fall and are renewed the next season, the trouble can be continued only by a new infection; in other words, only one season’s growth and function is involved. There are, however, a few fungi which not only reduce the assimilating leaf area but even cause the premature fall of the entire leaves, and these fungi are, of course, the more injurious. The most common leaf fungi are those producing the spot diseases, the foliage being covered by spots varying in color, size, and shape, which mark the destroyed tissue. Some- times the destroyed tissue dries out, becomes brown, and breaks out under action of rain and wind, the leaves remain- ing perforated as by shot. Another class of fungi produce the so-called powdery and other mildews, recognized by a whitish or else black spider- web-like growth on the surface (the fruit-bodies), which becomes powdery. While the spot diseases and mildews affect mainly the broad-leaved trees — maples, chestnuts, oaks, and many others — the rusts, characterized by collections of yellowish red, somewhat powdery fruit bodies are more frequent on conifers. These attack also stems and branches, causing peculiar swellings or knots and blister-like patches. Here also belongs the disease known as juniper apple, which appears on the red cedar with a fruit body of slimy or gelatinous, yellow or brown, conical masses. On the whole, all these fungi are of minor importance and, if the trees are otherwise kept in vigorous condition, their damage is in most cases readily repaired. ing , the two white spots on the wound be fruit bodies of the fungus. erous cherry tree Fic. 10. —A cank 40 Disease and Death of Trees — Generalities The “black” fungi, which attack the bark, find entrance through small wounds made by hailstones, insects, or break- ages. Working between bark and wood in the bast or bark portions of the cambium and into the wood, they destroy living tissue, and, if the injury is extensive in younger trees and twigs, they become dried out and killed. These bark-fungi are found especially on conifers, pine, spruce, fir, etc. Their presence is usually not discovered until a number of pin-sized, white, black, bright red, or yellowish pustules or spots — the fruit-bodies of the fungus — appear on the outside of the dead bark. In deciduous-leaved trees the same class of fungi produce malformations known as canker. On small areas of irreg- ular shape the bark is killed, and in the attempt to heal the damage by callusing each season, and at the same time in the continuance from year to year of the fungus growth, all kinds of curious shapes of the wound are produced. Small fruit-bodies, white with minute red spots, appearing on the dead bark of the margin of the wound are the indications of the fungus causing these malformations. Similar to this disease is the black-knot of the plum and cherry trees, a fungus producing swellings of irregular shape. By reducing the water-supply, especially in dry years, these bark-infesting fungi cause sometimes the partial or entire death of twigs and branches. Various fungi working on young trees and on foliage give rise to swellings of the leaves like boils, and to the curious deformations known as “witch’s broom.”’ Timely removal of these arrests the progress of the disease. The condition and age of the tree determine, to a large extent, how far these fungus attacks may be detrimental. The vot fungi, which produce the decay of wood, are the Fungus Diseases 4I most common and the most insidious, since their mycelium penetrates deeply into the body of the tree out of reach. Since the trunk of the tree, the wood, is mostly dead tissue, Fic. 11. — Three species of rot fungi. When these fruit-bodies appear at the base or on the wounds of a tree, the interior is usually all decayed, and help comes too late. (After Murrill, from Cornell University Bulletin, No. 205.) they do not impair to any great extent the living portion. Yet they are not mere saprophytes, for they really feed on the wood, absorbing cell-walls and cell contents, and to some extent impair its functions in the conduction of water. But their main damage lies in destroying the firmness of 42 Disease and Death of Trees — Generalities the wood body. While the tree can go on rotting for years, to all appearances without detriment, its stability is under- mined, and finally a windstorm may lay it low in full leaf and otherwise in full health. These fungi gain entrance to the wood through wounds made by broken or badly pruned branches, by broken bark or through injured, exposed roots. On the ragged surface of a broken branch stump, and even on a well-pruned but unprotected wound, dust and water collect and form a seed bed on which the fungus spores — cor- responding to the seeds of other plants, minute or microscopic, easily scattered by the winds — can locate and sprout. These grow into the wood by rootlike hy- phe, which bore through and between cell-walls, branching mul- tifariously and forming a mass of white meshes penetrating the wood in all directions—the so-called Fic. 12.— “Shelf” fungus on. the stem of a pine. a, sound wood; , resinous “light” mycelium. ‘This draws its suste- wood; c, partly decayed - : wood or punk; d, layer of Nance from the tree, aestroying living spore tubes; ¢, old ¢el]-walls and absorbing cell con- filed up spore tubes; f, fluted upper surface of the tents. As a consequence the wood fruiting body of the fungus, se S- : : oe THON EARS (ood ee dries, shrinks, cracks, turns reddish a great number of fine brown, or else becomes spongy and threads (the mycelium), its A om vegetative tissue penetrating Yellowish white. The mechanical the wood, and causing 1S destruction proceeds as the ame decay. (Department of 3 3 Agriculture, Division of For- celium proceeds. estry Bulletin, No. ro.) . : Finally, sometimes after years, the mycelium forms a fruit-body on the outside of the tree, the readily recognized toadstool making its presence Fungus Diseases 43 known to the uninitiated long after the mischief has been done. On the roots, besides the rot fungi, there are found others which attack the living parts and hence become directly a damage to the life function of the tree. While here too, as a rule, an injury or weakened condition invites the fungus attack, there are fungi which appear to attack perfectly healthy and uninjured roots. Thus the southern root rot which infests a large number of tree species, kills the roots so extensively as to produce a sudden wilting of the leaves and subsequent death of the tree. Poorly drained and poorly aérated soils seem to favor its develop- ment. The honey mushroom also kills young trees and weakens or stunts the growth of older trees which finally, if a dry, hot season occurs, may dry up for lack of water-supply. Its mycelium grows not only in, but alongside the roots through the ground, within a few inches of the surface and thus spreads from tree to tree, increasing the area infested. Some few plants other than fungi may be found as para- sites on branches and bole; they are mischievous, although rarely of importance unless extraordinarily developed. Among these are various species of muzstletoe, which occa- sion objectionable burl-like malformations, due merely to the mechanical obstructions to the wood growth which their roots, imbedded in the cambium layer of the host, produce. The dying of the branch above this burl may be the con- sequence. ‘The trouble is spread by the seeds of the mistle- toe, which are covered with a sticky substance and are carried by birds to other branches and trees; hence its spread, at least, can be prevented by removing the affected branches. In addition to the parasitic fungi and other parasitic plants, there will be found on all trees epiphytes, ze., 44 Disease and Death of Trees — Generalities plants which do not feed on the host plant, but use it simply as support, such as mosses and lichens, orchids and various climbers, like the Virginia creeper. As a rule, these are of little consequence; yet if in excess may become troublesome. The excessive development of mosses and lichens on the bark is a sign either of a very humid atmosphere, of very wet soil, or of very slow growth of the tree. In the latter case, the outer bark is sloughed off very slowly, thus giving time for the epiphyte to develop. Usually there is no damage to be anticipated from the epiphytes, but, if exces- sively dense, the cover of lichen and moss may become injurious by closing the breathing pores of the bark, and had better be removed. Creepers are usually harmless, but may become objection- able on young trees and young parts, like wires or artificial ligatures, if the pressure with which they resist the expansion of the body of the host plant becomes so great as to retard or prevent the supply of formative materials to the portions below the constricted part. In such cases the lower portion will be retarded in its diameter growth. Insect Damage. A host of insects belonging to the orders of beetles, moths, butterflies, gall-flies, saw-flies, plant and bark-lice, are parasitic on all parts of trees, feeding on leaves, twigs, cambium, roots, and wood. Sometimes it is the imago, the beetle, that does the mis- chief, but mostly it is the larva, the grub or caterpillar, which is to be feared. Some live and feed on the exterior of the plant, especially those which depredate the foliage, others are internal feeders, living during some stage of their development within some part of the host plant. Such are the gall-insects and leaf-miners, which lay their eggs in the soft tissues of leaves, leaf-stalks, or fruit, where the larva develops and feeds. The larve of the bark-beetles feed Insect Damage 45 on the soft cambium layer underneath the bark; the stem- borers hollow out twigs or make their abode in the trunks, feeding on the wood itself. Some do little or practically no damage; indeed, in the majority of cases only when an extraordinary development of an insect pest in any one séason takes place, or when repeated invasions have to be endured, or when other acces- sory unfavorable conditions occur, need any apprehension for the life of the tree be felt. Such unusual developments of insect pests seem to take place periodically, when, due to specially favorable seasons or otherwise, the pest is favored, while natural enemies are reduced or less favored. The leaf-eaters of certain species are especially liable to this periodic excessive multiplication. If the defoliation is only partial and occurs at a time of the year when the foliage can still be replaced by the development of the dormant buds, outside of the temporary unsightliness, only a reduction in the season’s growth is the result. But, if the defoliation is complete, and, as happens with some species “f leaf eaters, more than one generation is developed in a season, repeating the destruction of the foliage as new leaves are formed and thereby preventing the assimilation of food materials, the tree may be weakened even to death. At least a repetition of the defoliation for two or possibly three seasons, according to the vigor and age of the tree, will be fatal. The new foliage, formed in the same season after the first defoliation, is apt to be smaller in size or abnormal in form and thinner, hence less effective. Sometimes, however, when a large number of buds have been destroyed, unusu- ally large and abnormally formed secondary leaves arise from the few remaining buds. In either case the nutrition of the tree is interfered with. 46 Disease and Death of Trees — Generalities While some insects are general feeders, 7.e., attacking all kinds or at least a number of tree species, insects, even more than fungi, are partial in selecting their hosts, ¢.e., given species of insects attack given species of trees. Besides, they differ much more in their life habits than fungi, hence they may not be dealt with as a whole, like the fungi, but it becomes more needful to know them specifically by name, appearance, and habit, with their life history, in order to apply judiciously measures for their reduction. Moreover, there are a number of enemies of the obnoxious insects found in the insect world, and it becomes necessary to dis- tinguish between friend and foe, in order not to destroy the natural enemies of the pest. We can here refer specifically only to the more common pests of ornamental and shade trees, leaving the vast num- ber of minor and of orchard pests to be studied in the specific literature. Fuller descriptions will be found in Chapter VI; here only the character of the damage in general is to be discussed. With regard to the manner in which.the damage is inflicted, we can classify the injurious insects into a few groups, each group containing representatives of the yarious orders into which insects are scientifically classified. These groups may be called leaf-eaters, ledf-miners, ieaf-rollers, leaf- suckers, gall-insects, bark-lic rk-beetles and borers. The character of the damage itself may be threefold, namely, destruction of substance, occasioned by leaf-eaters, _bark-beetles or borers; loss of sap occasioned by plant-lice; and formation of abnormal excrescences or galls, to which the plant is stimulated by various insects. All three kinds of damage or any two may be occasioned by the same pest. The Jeaf-eaters are mostly caterpillars of butterflies and especially of moths, which in feeding on the foliage generally Insect Damage 47 destroy the entire leaf. But the larve of beetles also, and some of the beetles themselves are destructive in this manner. The Jleaf-miners, which skeletonize leaves, eating only the softer portions in patches, also come from different fam- ilies. Some of these, like the elm-leaf beetle and the larch- miner, make such extensive inroads, that the result is very much like the eating of the whole leaf. Others make only small, blotch-like mines or short tracks on upper or lower, or both sides of the leaves, destroying small areas of the soft tissues. These, as a rule, do little damage. Neverthe- less it is wise to reduce them by burning up the fallen leaves, in which they usually hibernate. Another set, the /eaf-rollers, also coming from different families, roll the leaves together in various ways to make shelter for the caterpillars, folding the edges and sewing them together with silken threads, or spinning them, as in the case of needles of conifers, into a web. These distor- tions and occultations of the foliage would generally be of little consequence, but the insect, here sheltered, usually is destructive to the buds and young shoots, and, if the leaves in the web are eaten, as is done by some, the damage may become considerable. While the leaf insects so far mentioned feed on the foliage by eating it, there are a few, like the plant-lice and leaf- hoppers, which suck the sap by piercing the succulent leaves and leaf stems or even twigs, causing the leaves to crumple or roll, or producing gall-like swellings. Usually these leaf-suckers do not do much damage unless unusually abun- dant. There are, however, some bark-lice which do much more damage by puncturing the bark of twigs. To this group belong also various scale-insects, which, adhering to the small limbs, sap their life and cause them 48 Disease and Death of Trees — Generalities to dry up, and even large branches and entire trees can be killed by these scale-insects if they are abundant. A very large number of insects coming from several of the various orders, inhabit the foliage and smaller twigs in their egg and larval stage and produce what is known as galls, peculiar swellings, tumors, or malformations, often highly colored. Especially the family of gall-flies, number- ing some hundreds of species, inhabit largely the oaks, producing all sorts of leaf-galls. Among these are the galls of commerce from which ink and gallic acid are manufactured. The damage is too small to deserve much attention, but where excessive, the leaves should be gathered while green and burned, to get rid of the deformation. These swellings or malformations of twigs, buds and shoots are often accompanied by a shortening of the annual growth and a crowding of the foliage, forming what is known on willows as the “willow rosette’’ and on pines or on spruces as the “pine-apple.”’ The saw-flies, similar to the gall-flies, lay their eggs in the tissues of the leaf, but as they live in colonies and have often two broods in a season and their larve feed voraciously, they are more injurious than the gall-flies and may, as in the case of the larch and the pine saw-flies, cause widespread havoc. ‘The conifers suffer especially from these pests. With the family of beetles known as weevils we come to the stem-boring insects. For, although some feed on the foliage and puncture the bark, their worms or grubs inhabit not only the fruit but also the young twigs; the beetle with its long cylindrical snout perforating the bark and depositing an egg in the hole, the larva developing from it, burrowing beneath the bark, loosening it from the wood or boring into the stem and destroying the wood. Bark-beetles, the “grubs”? of which live under the bar’ Insect Damage 49 especially of coniferous trees, and feed on the soft cambium layer, are usually secondary troubles, after the vigor of the tree has been undermined by defoliation, by fire, or by other causes. They rarely attack vigorous and healthy trees; sometimes, however, when a pest is excessively abundant, healthy trees may be attacked and succumb, especially young specimens. Since the larve of these beetles destroy the cambium, their damage becomes easily very serious, leading to the death of the tree. And as their presence is not readily detected before the mischief is done they are most difficult to deal with. Not less insidious and difficult to combat are the wood- borers and wood-wasps which burrow in the wood, or hollow out the pith of twigs. Although they are mostly less injuri- ous to the tree, being usually few in number and working as they do in dead wood, yet when they attack the smaller branches and young trees they may cause undesirable loss. Even in the bole of older trees they may, if very numerous, undermine the vitality of the tree by reducing the conducting tissue so as to eventually cause the death of the less vigor- ous individuals. Moreover, these boring insects may pro- duce mechanical injuries which furnish an entrance for fungus growth and thereby lead to more serious trouble. The roots suffer also from a number of insects. Some of them destroy the youngest root tips mechanically, as is done by the mole-cricket and the larva of the June bug, while wire- worms and other beetle larve, and a few caterpillars and root-lice living underground, feed on them, and others again burrow in them. The damage is usually of moment only in young trees and is, of course to be found in the loss of feeding apparatus. There should perhaps ‘here be added, since the question occasionally arises, a few remarks on “how to kill a tree.” 50 Disease and Death of Trees — Generalities It is easy enough to get rid of any tree by cutting it, or by merely girdling, and, if it is a “sap-wood” tree, by sawing through the sap-wood, thereby cutting off water-supply from the foliage and food-supply from the root. While this works positively with conifers and many _ broad-leaf trees, there are some of the latter, which have such vigorous sprouting habit from the root that something more must be done to kill the root-stock. Removal is, of course, again the most effective but expensive method. With some, cutting through the root strands will expedite death; but others are so persistent that still another means must be added. The most effective of these and least destructive to other vegetation, is the thorough drenching of the root- stock with kerosene which closes the breathing pores and chokes out life. CHAPTER. IV DIAGNOSING OF DISEASES UST as the physician finds his greatest difficulty in determining the cause of illness, so the tree doctor, although knowing the diseases to which trees are liable and knowing the remedies, may still find trouble in diagnosing the true cause of the evident abnormal condition. Here it is that experience and judg- ment come in, yet sometimes even an expert remains doubt- ful. Nevertheless, by careful examination, in many cases even the less experienced can determine what ails the tree. Usually, if anything is the matter in any living part of the tree, the foliage gives the first indication, and furnishes the most readily available symptoms for diagnosis. Hence our examination begins with the foliage, to see whether it shows any divergence from normal conditions in size, quantity, form, or color. With a conception of what the normal foliage ought to be, we ascertain whether the leaves of the individual under examination are smaller than usual, or thinner, whether the foliage as a whole appears slim, whether the leaves are wholly or partially discolored, whether they are mechanically injured, eaten, crumpled, or otherwise misshapen, spotted, wilted, or dead. If no local cause, as from fungi or insects, can be ascer- tained as surely responsible, we look next for indications on twigs, branches and bole as accounting for sickly appear- ance of the foliage or death of branchlets. Mechanical 51 isp) Diagnosing of Diseases injuries to the cambium and young wood, caused by insects or other agencies, and the robbery by sucking insects like the scale and bark-lice, affect the feeding processes of the tree and may be the reason for the abnormal condition of the foliage. If only certain portions of the foliage show abnormality, it is almost certain that a localized cause will be found such as a colony of insects, a partial destruction of food-conduct- ing tissue, a particular root injury. If, on the other hand, the whole crown is affected, the cause must be more general and may be found in general conditions of nutrition. Then it becomes necessary to examine the soil, to see whether in any way conjectures as to the conditions at the root may be formed, accounting for the indications in the crown. Here, in the root region, matters become more compli- cated because hidden from direct observation, and yet here lies probably the most fertile source of trouble. As so often in an old man head and feet become feeble simultaneously, so in the tree, when the top gives out, there is usually something wrong at the root, and that means generally at the very extremities, — the root-tips. The dis- tance from root-tip to branch-tip, from pump and power plant to feeding extremities, increasing continuously, makes naturally the life processes more and more difficult to per- form at the extremities, and if any other cause of discomfort is added, the result may be fatal. As on the leaves and bole, so on the roots, there are predatory insects and fungi active and the roots are liable to mechanical injuries with the same results. But, in addi- tion, there are essential conditions in the soil, the medium in which the roots live, which can change to a much greater extent than can those of the air, the medium of the upper portions of the tree. As we have already seen, these changes Insect Damage 53 involve the water-supply, the supply of oxygen, and the supply of nutritive elements. The most common symptom of unfavorable soil condi- tions is found in the paling or ef¢zolation of the leaves, which become prematurely yellow, wilting and falling before the end of the season; while in other cases the leaves and buds are reduced in size. Branch-tips, especially of horizontal branches, are killed back, and the top of the crown dries and dies, giving rise to the so-called staghead; or else water- sprouts, slender, long, wisp-like shoots out of the regular order, are formed. Excessive growth of moss and lichen may also be an accompanying symptom. If the tree has been vigorous before, and has only recently shown signs of weakness, we must note especially any changes lately made in the soil conditions, which may account for change in its vigor; such as the cutting down or filling up of ground, making ditches, laying gas-pipes, draining or flooding, cultivating or sodding, performances which are apt to interfere with the root system, altering its environment, and hence the amount of active root growth. If none of these investigations give a clue, we must then inquire into the weather conditions and the history of the preceding two, three, or four seasons, as well as into sur- roundings generally, and we must ascertain what has been the previous treatment of the patient. Thus circumspect investigation and observation and historical evidence must be brought together to diagnose the more complicated cases, while in other cases the initiated may be able at once to determine the cause of the abnormal condition. The novice will have to examine with more care, especially to avcid the mistake of recognizing as the pri- mary cause what is only secondary. Insect Damage. ‘The most obvious damage is that done 54 Diagnosing of Diseases by the leaf-eating insects. The only trouble is, that when the damage has become apparent, it is either too late, or very difficult, for that season at least, to combat them. Since in these cases preventive measures alone are effica- cious, it is desirable to secure, in due time, evidence of the probable appearance of large numbers of these pests, or else, as a matter of precaution, to apply preventive measures (spraying poisons) even without that evidence. In the German forest administrations, trial collections of the hibernating insects are made every spring to deter- mine whether necessity for preventive measures exists. Cocoons, caterpillars, and beetles are collected from under the bark of stems and from under the moss and rubbish at the foot of the trees, and an estimate of their probable number is made. In parks, similar precautions can be practised to advan- tage, and the collection, instead of being a trial one, may be one directly destructive of the pest. Observation of other signs, which, however, require the eye of the practised entomologist or dendrologist, leads to a recognition of the impending danger. The number of insects observed in previous seasons may also be used as an indication of what to expect in the follow- ing year, since insect pests are apt to grow from year to year until a climax is reached and their progress checked by natural enemies or by an untoward season. In city streets, where only certain species of trees are planted and the same species lines street after street, the development of insects depending on that species is naturally favored: a city of elms is also a city of elm-beetles. Hence, one may expect here a yearly incursion, and preventive measures should be taken as systematically as street clean- ing, or as any other regular public function is performed. Fungus and Bacterial Diseases 55 If the timely examination of insect conditions has been neglected, then the diagnosis will be made when the dam- age has begun or has progressed to some degree. The insect can be observed at work, the culprit captured and its name or character determined. With the leaf-eaters this is usually readily accomplished, but the sucking insects whose damage is not at once apparent, as well as the bark- beetles and borers are discovered by close observation only. ‘The small round entrance holes in the bark of conifers, accompanied by resinous exudation, and finally the loosen- ing of patches of bark where the cambium has been de- stroyed give evidence of the presence of bark-beetles. The presence of borers is indicated by the entrance holes, usu- ally near the base of the tree, and by the excreta or finely divided wood particles, wood-flour, found at the base of the bLEe: Fungus and Bacterial Diseases. ‘The fungus diseases of the foliage make themselves known -by the partial dis- coloration of the leaves, usually in spots of various colors, and by the powdery aggregations of fruit-bodies, silky, smutty, or otherwise. Sometimes also the foliage wilts or dries up. As there is only one practicable remedy for all these fungi, namely, spraying with poisons, it is not necessary to be familiar with the different kinds, beyond recognizing their existence. The same can be said of the rot fungi, which practically behave alike, and are treated alike. Dis- coloration of the wood in wounds, and whitish or yellowish mycelia strands breaking through the tissues, and finally the fruit-body proclaim the presence of rot fungi. The dying of portions of the crown on account of reduced water conduction may also be due to these fungi. 56 Diagnosing of Diseases The existence of the root rot which produces stunted growth and eventually death, may be determined by close observation in finding a whitish, yellowish, or dark brown growth of loosely interwoven, hair-like mycelium threads on the root surface and in decaying tissues, or in the soil itself. This mycelium will also be found between wood and bark in whitish leather sheets, and will grow into the bark at the base of the tree above ground, finally producing here and on exposed roots the readily recognized fruit- body. There is at least one insidious disease, known to be due to bacteria, a disease peculiar to North America, and famil- iar under the name of /ire-blight, which attacks the trees of the apple family, and especially the pears and quinces, but also the mountain-ash, service-berry, and hawthorn. It is evidenced by the browning and subsequent blackening, first of the leaves and finally of young twigs and shoots, starting at the tips and progressing downward until even the larger branches may be infected. The bark of the diseased branches cracks, and a thick, blackish, gummy fluid exudes, the bark later drying up and shrinking. The disease may even descend into the trunk, then resembling swn-scald. Curiously enough, healthy, vigorous, well-fed, and well cultivated trees are more liable to this malady than less thrifty ones, new succulent growth favoring the disease. There is but one remedy, namely, to cut out and burn the affected parts well below the discolored portions. This should be done during winter or spring, or in the fall after the trees have stopped forming wood. Checking the amount of moisture in the soil, as, for example, by the growth of grass or clover, will reduce the succulent growth and pre- vent the disease. Physiological Diseases. Whenever local causes of the Effect of Soil Conditions 57 diseases of foliage are present, such as those produced by insects or fungi, the diagnosis is comparatively easy and the remedy readily suggested; but in the absence of such local disturbances, when the evident abnormality of the foliage is due to more remote causes, the difficulty is greater. As long as fungus growth or insect depredations on bark, wood and root, can be discovered as likely to have produced the disturbance in the condition of the foliage, even a layman may find the cause; but to diagnose the so-called physiolog- ical diseases which are due either to permanent changes, or to some unusual temporary conditions in the environment, the services of an expert may be required. Changes in the conditions to which the tree was originally adapted may take place in the soil or in the light supply (when neighbors are removed or are crowding), or they may simply be in the weather conditions of the particular season, or, in many cases, the combined conditions of soil and season effect the sickness. Indeed, whenever the conditions of nutrition are inter- fered with, the foliage will soon give evidence of it. And in this connection, the soil conditions, especially the mechan- ical conditions which influence water and air supply, are of the greatest importance, as these are the ones which can be more or less controlled. Effect of Soil Conditions. It must not be overlooked that a soil changes in its stucture and thereby in its capacity for water conduction and aération by the compacting of rain- drops, by frost, and in many other ways, so that the same soil which was originally satisfactory to tree growth, may in time become less so. Not only soils exposed directly to rains, but also those under sod, or even under sidewalks, become constantly more and more compacted, and hence a gradual change in their permeability to water and air takes 58 Diagnosing of Diseases place, until in an unfavorable season this reduction of water and air becomes fatal. Moreover, as the root system expands it enters new regions and possibly less favorable strata than it occupied before. Therefore, whenever direct visible causes are absent, an examination of the soil conditions, especially those of water supply and aération, furnishes in most cases the basis for the diagnosis of disease. Excess or deficiency of water, and deficiency of air at the root produce very similar results in the appearance of the tree above ground. Pale or yellowish foliage, undersized leaves, short annual shoots, or long spindling ones poorly foliaged, and finally the dying of branch tips are the results of a compact heavy soil. Especially is this true in a cool wet season, when, owing to the excess of water in the soil, air (or oxygen) is excluded from the roots, and their respiration rendered imperfect. In newly planted trees, especially in compact soils, these same symptoms, followed by death, often appear as a consequence of too deep planting. The aération of the roots and lower portions of the tree being thereby precluded, alcoholic fermentation of the cells sets in, and the water- conducting function of the cambium and young wood is impeded, as becomes evident from the sickly yellow appear- ance of the foliage. If the soil is not corrected, in a year or in a few years the tree succumbs. Some species, however, such as willows, poplars, elms, and basswood, may under these conditions form new superficial roots from the bole and thus help themselves. A surplus of water in the soil, besides unfavorably influenc- ing a€ration and thereby producing the symptoms mentioned, may also produce a kind of dropsy, if weather conditions are favorable to rapid transpiration or if light conditions in Effect of Soil Conditions 59 the foliage have been changed: an excess of water will cause an excess of cambial activity, and this may cause the bark, especially on young twigs, to burst open in spots, from a few inches to a foot, exposing the wood. This is found very frequently on currant bushes, but occurs also in oak, horse-chestnut, and beech. ‘To correct this and some other similar conditions, the expert surgeon applies a blood-letting process, making a longitudinal cut through the bark, whereby the pressure is relieved; such a wound soon heals. In other trees, like the silver maple, the excessive growth sloughs off the old bark, rapidly exposing the younger bark. This may be followed up by sun-scald — the drying and breaking open of the bark — with the consequences usual to mechan- ical injuries. A great number of malformations in young shoots, foliage and fruit are also attributable to excess of water-supply at the root. A very common result of the change in the relation of consumption to supply of water, as for example, when a tree is severely pruned, or in the case of mere excess of water at the root, is the formation of so-called water-sprouts, or suckers, — very vigorous thin long shoots, which arise form dormant buds out of regular order along the branches and bole, particularly near cut branches. These may or may not be injurious. They interfere, however, with the sym- metrical development of the crown, and they are injurious when they rob the main branches of water and cause their drying out. They should therefore be removed, and at the same time the water-supply at the roots regulated. Thus, while excess of water on compact soil becomes injurious through the impeded aération of the root system, deficiency of water in a drouthy season produces similar results by the failure to supply the stream of transpiration 60 Diagnosing of Diseases from the foliage, the newly formed rootlets dying in the dry soil. This results in premature yellowing of leaves on single branches, a shortening of the year’s shoot and the drying out first of portions of the bark and finally of entire branches. In light sandy soils this deficiency of water at the root may be due to over-drainage, or, in compact soils, to the packing and caking of the surface layers, preventing aération as well as the penetration of water. This hindrance to penetration, especially in paved and asphalted streets, grows more and more pronounced from year to year, and hence premature loss of vigor is the consequence unless assistance is given at the root. Since trees get their water-supply from great depths, the drouth must be very protracted before the effect is felt, except in shallow soils, on rocky ledges, etc. Yet, in our country, there occur seasons, when the drouth is so severe and protracted that even well-established specimens of native trees, such as Rock Maple, and White Pine, have their leaves badly scorched. The leaves then do not fall, but become brown and dry, and remain hanging on the twigs. A very similar appearance of foliage in early spring, espe- cially in conifers and other evergreens, such as Rhodo- dendrons and Buxus, is due to winter drouth. This is experienced usually when, with the ground still frozen, a sudden rise of temperature occurs and dry winds prevail which overtax the transpiration current from the leaves. This “burning” of the leaves is chiefly confined to that side of the tree which is exposed to the prevailing winds. In fruit trees there are quite a number of other symptoms due to deficiency of water which do not concern us here. Different species make different requirements on water- supply, some adapting themselves to deficiency or excess Effect of Soil Conditions 61 more readily than others. These latter, like the Swamp Oak, Bald Cypress and Alder, especially when they have once adapted themselves to swampy life are at a great disadvan- tage if the conditions are suddenly changed. It is, there- fore, possible that in newly planted trees any ailment is merely due to change from one set of conditions to another, to which the tree is not as yet adapted. Thus a tree moved from a shady position to one of more intense light will suffer for a time until the foliage is adapted to the new enyiron- ment. In passing it is interesting to note that even a physically moist or wet soil may be physiologically dry, that is to say, the water may not be available to the rootlets. ‘This is the case in swamps where the water is saturated with humic acids from the decay of vegetable matter, these acids having a greater attraction for the water than the rootlets can exer- cise. Here we see quite frequently the disease called stag- head, which consists in the drying of the top due to deficient water-supply at the root. It is, therefore, necessary to be cautious in the attempt to diagnose and correct water conditions. The death of the top, top dryness or staghead, is gradual, the lower branches remaining green, their annual shoots, however, becoming shorter. It is a result of drouthy con- ditions at the root, which may be caused in various ways, other than the one just cited. In forests and parks, by cut- ting out or burning the undergrowth and by severe trim- ming, the sun is given access to the ground. As a consequence the decomposition of the litter and humus which covers the soil proceeds more rapidly, while at the same time on: account of the increased light supply the foliage becomes more active. Stimulated by the increased food elaboration, all the benefited trees at first grow more vigorously and their 62 Diagnosing of Diseases foliage is greatly increased, but finally, after a year or more, a disproportion of supply and demand arises, and, as the lower branches appropriate a greater share of the water and minerals from the soil, the upper ones are starved and die. We will see later that electric discharges may also cause this stagheaded condition. Although water is the most important contribution of the soil to tree growth, — most soils containing sufficient quantities of the needful mineral nutritive elements — yet, sometimes a deficiency of the latter in available form may account for sickly appearance of the foliage. Hence the chemical constituents of the soil should also be exam- ined. If the premature yellowing of the leaves and other abnor- mal appearances do not find any other explanation, they may be due to deficiency in iron, magnesium, potash, lime, phosphoric acid or nitrogen, and the application of appro- priate fertilizers will correct the evil. The deficiency most likely to occur is in nitrogen, of which trees require a relatively large amount. The absence of nitrogen in sufficient quantity is indicated by the etiolation of the foliage, which assumes a yellowish or even a whitish appearance. It will have appeared from the foregoing statement that, while the foliage gives sure indications that something is wrong, it is not so easy to decide what is wrong. Different -causes may produce the same abnormal appearance and the same behavior in foliage and twigs; just as the paleness of the human patient may be due to various causes. The abnormality may be primarily due not to local, but to more remote causes, which affect the whole physiology of the tree, and often the secondary evils, which, to the Atmospherical Influences 63 uninitiated, appear as the true source of the disease, are’ merely the result of the unfavorable physiological condi- tions of the tree. Hence in diagnosing, one should never be satisfied to stop short of an examination of the condition of the patient in all directions. Atmospherical Influences. The conditions of the atmos- phere naturally also influence the functions of the tree, but are mostly not under control. Here, too, species vary in their requirements and in their capacity for adaptation. Here even more than with reference to soil conditions (which are under control) it is necessary to make sure of the natural adaptation of the tree to its surroundings. And, we reit- erate, it is not only the species that need consideration, but the individual itself, when transplanted from one set of conditions to another. For, the individual tree as it grows up from the seed has the capacity of adjusting itself to its ‘environment, but when suddenly transplanted into other surroundings it cannot do so at once. Hence it may be ailing for some time until it gradually adjusts itself, or else it may succumb to the unaccustomed conditions, either directly or by physiological disease, or indirectly by falling a prey to parasites in its enfeebled state. If, in planting, species or specimens have been chosen which are adapted neither to the conditions of humidity or drouth, nor to the temperature changes of the atmosphere common in their new home, they will suffer, and perhaps die, and should be replaced by those which are better suited to the environment. Theoretically, it may be possible to help such exotics by regulating the soil conditions, and to mitigate climatic conditions by screens and other protec- tion; but practically this is usually too troublesome. Soil and atmosphere are in such interdependence as far 64 Diagnosing of Diseases as the life functions of a tree are concerned, that the influ- ences of the one may be counteracted or increased by the influence of the other: drouthy conditions of the atmosphere may be met by irrigation at the root; cloudy weather may counteract deficiency of water at the root; a warm soil may start growth so early in the season that frost will do dam- age, which otherwise would have been harmless. These relations involve complications which may baffle even an ex- pert’s diagnosis as to the true cause of physiological disease. The humidity and temperature of the atmosphere are conditions of moment, especially in frost phenomena, but the soil plays in these no subordinate réle. Indeed, many frost phenomena are more dependent on soil conditions than on temperature. Stiff, clayey soils are, as a rule more liable to frost than light soils, and a soil producing over-luxuriant growth is apt to expose the imperfectly ripened wood to damage by early frosts in the fall. There are three seasons in which frost may occur with differing effects, namely, the fall or early frosts, the winter cold, and the spring or late frosts. The early frosts occurring in the fall at the end of the grow- ing season will be felt especially by those leaves which have not been shed, and by the tips of the shoots which have not perfected their growth. Damp locations seem to induce this late growth, or at least do not seem to mature the wood as well, and they are also more liable to fall frosts than drier regions, hence draining may reduce the frost danger. In certain positions the danger from frost is greater than in others, and, if this is due to cold air settling in a given place, say a group of trees, it may be corrected by opening up the group and thus creating a draft for the cold air to draw off. Conifers may suffer especially in such “frost holes.” Atmospherical Influences 65 The proper treatment for trees whose shoots have been frost-killed, is to head them back severely to sound wood in order to get rid of the injured, and to supplant it by active, healthy growth. This pruning is best done shortly before the foliage starts, when the extent of the injury can be better noticed. Trees or branches thus injured by fall frosts may sometimes leaf out and bloom in spring, but they soon succumb for lack of sufficient water-supply through the injured parts. The loss of foliage with the approach of winter, which is a natural physiological process, is more or less connected with changes in temperature conditions, and hence in some years may occur earlier, in others later than usual, without being a sign of sickness. Besides leaves, certain species, like Elm, Linden, Black Locust, Poplar, Willow, Oak, Bald Cypress, and many others shed more or less regularly whole branchlets, from one to ten years old, and more. This phenomenon may also be considered pathological, although it occurs quite frequently, and sometimes regu- larly and systematically. Neither the cause nor the rem- edy is known. This shedding of branchlets is entirely different from the loss of the tips by frost, regularly experi-— enced by some species like Linden, Elm, and Sycamore, and by exotics which find the summer too short to finish their growth. This habitual freezing back can be prevented by defoliating the branchlets before growth ceases, when the wood will harden before the frosts come. In other species such loss of the young twigs occurs only under special conditions, namely, when the young wood has not been matured in time. This is apt to happen when a late and warm moist fall follows a dry summer, inducing belated growth which does not harden but remains succulent and is nipped more or less severely by the early frosts. 66 Diagnosing of Diseases Late pruning in summer will produce such late growth and is, therefore, to be avoided. The late or spring frosts will injure mainly the new tender growth of leaves and flowers, and the opening buds. A temperature from two to even seven degrees above freezing point may suffice to do the damage. Southern, eastern, and southeastern exposures are especially dangerous, for in these sun-warmed situations vegetation awakens in early spring and the tender foliage falls readily a victim to the late frost. Shade, or any other method of keeping the soil cool and retarding the activity of roots and buds is the only means of counteracting these frosts. In most cases they have to be endured, or avoided by selecting late budding species and varieties. Winter cold, as a rule, does not do much damage, yet occasionally very severe and persistent cold, causing frost to penetrate the soil to a great depth, may become detri- mental, injuring or even killing trees and shrubs. This is especially true when the preceding season has been unfav- orable, or for other reasons the plants have had their vitality impaired. Soil conditions and situation have considerable influence on the occurrence of winter killing, just as they have on early and late frosts; high, dry ground and exposed places being especially subject to this damage. Even native species are by no means exempt. The loss may be only in buds, or in twigs, but, if the roots are killed, the entire plant may succumb. During the severe winter of 1903-1904, Red Maple, Butternut, and White Pine in the State of New York were killed outright, and a long list of trees and shrubs were partially killed. The loss of part of the root system may exhibit itself, as in any other case of reduced water-supply, in the loss of part of the crown Atmospherical Influences 67 and a thinning of the top, or in under-development of the foliage, the latter being smaller, assuming a_ pendulous position and early fall coloring. The best preventive, where this kind of loss is anticipated, consists of pruning and mulching well, in order to restore the proper balance between root and crown. Winter cold will, of course, affect the young and imma- ture twigs in the same way as do the late frosts. In smooth-barked trees, such as the Beech and Horse- chestnut, and in special situations, the bark of branches and young trees cracks in patches, and the cambium and the young wood underneath are killed. If such lesions are xtensive they may lead to the death of branch or tree. This injury generally takes place on the southwest side and toward the end of winter when rapid temperature changes are more common; a few warm days stimulate the cambium on the south side to premature activity; freezing weather following, these active areas are killed, the young wood cells and cambium shrinking away from them and the bark cracking and drying out. Often not until summer does the bark split and reveal the damage below. Such frost phenomena as the killing of the bark appear in very variable form, such as small frost boils, or smaller or larger frost plates, the dead bark splitting off from the live margins and rolling back, exposing the dead wood, which then is either gradually covered up by a callus from the marginal cambium, or else becomes infested by fungi. The worst form of these frost injuries is the malformation known as canker, in which fungus parasites also take part. Wet, cool localities seem to predispose trees to this disease, but severe pruning and manuring in the spring may produce the same effect; this curiously enough, seems to appear as an individual peculiarity which can be transmitted by 68 Diagnosing of Diseases grafting. Drainage of soil and more careful pruning will reduce the disease. The cankerous parts should be cut out to the living cambium and covered with hot tar, at the same time the exposed side should be partially protected by brush or boards, until the cambium overgrows the wound. Similar results, z.e., the bursting in longitudinal cracks and killing of the bark and of underlying wood portions, are produced by the so-called swn-scald, which is also espe- cially observed on the south and southwest sides of such smooth-barked trees as Beech, Apple, Pear, and also of the soft-wooded Basswood, Horse-chestnut, Chestnut, Ash, Plane tree, Birch, and Willow. It is an open question whether this is not due in part, at least, to frost, in conjunc- tion with the sun. Protection of the exposed side by boards or straw, or still better by a neighboring shady tree, will avoid the trouble. When the fall of a winter temperature is very sudden and very low (below zero) frost splits, due to uneven shrinkage of the wood in the interior, are produced in a variety of trees; especially in those with distinct heart-wood, the sap- wood shrinking more than the heart-wood, a longitudinal split results. These cracks usually close up during warm weather, a callus overgrowing the wound forms a ridge and the damage consists only in this malformation, unless fungi and insects gain access. Such frost splits occur very frequently in northern latitudes, even in the forest, and on very cold days with a noise resembling a gunshot. Obnoxious Gases. Finally, special conditions of the atmosphere which become more and more potent in our cities, namely, the smoke and other poisonous gases emanat- ing from factories, must be considered as causes of disease. The merely mechanical black coating of coal particles and soot which settle on the foliage will only slightly reduce the Obnoxious Gases 69 function of the leaves, while a still more serious injury comes from the sulphurous acid which accompanies the smoke of most coals, and poisons the foliage. A small amount of this acid taken up by the leaves suffices to do the mischief. In most cases, however, the movement of the air, and the chemical change of sulphurous acid into innocuous sul- pkuric acid produced by contact with the humid air, prevent the worst effect; but, if conditions are favorable, the smoke of a brick yard, for instance, may suffice to kill the foliage. Even the smoke from locomotives may become injurious in moist climates, or in certain locations, such as in narrow valleys, when it remains stationary for some time. We may mention such smoke-resistant trees as Sycamore, Poplar, Ash, Alder, Maple, and Elm. The duration of the poisonous condition of the air rather than the concentration of the poison is of moment. The first visible signs of poisoning are characteristic pale spots on the blades of leaves, which turn brown, while the veins of the leaves remain green; the normal water movement in the leaves is interrupted and the green tissues are disorganized, the tips and margins of the leaves being first affected and drying up. The effect is similar to that of drouth and sun- burn. If the trouble continues, the entire leaf becomes yellow or brown, except in the case of conifers, when the leaf-turns red. Finally the leaf rolls up and drops. The drier the air, the higher the temperature and the more intense the light, in other words, the more active the foliage, the more quickly are these effects produced. The effect is therefore greater in the day and less at night. The poison does not penetrate the tree, but remains in the foliage, and hence the effect is only that of defoliation in general, namely, reduction or loss of food material. 70 Diagnosing of Diseases Chlorine gas, developed by the burning of coal in smelters and in certain soda factories, as well as soluble metallic oxides from various manufactures, have similar effects. Only the systematic suppression of the smoke nuisance, which several cities, notably St. Louis, have begun, and the enforcement of factory laws (such as are operative in most European communities) to prevent the escape into the air of poisonous substances, will remove this cause of disease for which there is no remedy. The escape of illuminating gas produces similar effects. To injure foliage a large amount of this gas is required, such as the continuous vitiation of the air, which often takes place in the neighborhood of gas works or of natural gas wells. The effect is usually the dying of portions of leaves, the tips and margins especially turning brown and dry; sometimes the entire leaf becomes dry and withered, hang- ing, however, tightly to the branch. More frequently still does the escape of gas into the soil from leaky pipes do harm. Indeed, when we read that in 1905 the gas companies of Massachusetts experienced a loss of ten per cent. of the gas actually produced, we must conclude that gas leaks are a much more frequent cause of damage to trees in streets and parks than is usually sup- posed. It is probably the sulphuretted hydrogen, which, taken up by the roots, acts as a poison. The result of gas poison- ing may be only a partial or local dying of parts, namely, of those directly affected by the leak; but it may also cause death of the whole tree. The presence of the gas is detected by the odor when the ground is turned, and by a blue coloration of the roots or of the sap-wood, ascertained by boring or chipping. This gas kills the roots, and, as a consequence, discoloration and Electric Currents 71 premature dropping of leaves and dying of branches occur above the affected root. A characteristic outward sign for diagnosis is the darkening and rapid loosening and falling of the bark, similar to what occurs in the case of kerosene poisoning. If the leak is a sudden one and the gas escapes in a large quantity, a tree in full foliage may suddenly have its leaves droop and turn brown; these hanging on, however, till winter winds tear them off; such trees die in short order. In some cases trees have been known to have been killed by gas in a single night. If, however, the leak is slow and small, only a single root and its corresponding crown parts may be killed, but, if the leak continues and the gas spreads in the soil — which in loose soils may go on rapidly for a thousand feet or more, — general debility develops and the whole tree gradually succumbs. There is practically no recovery for a tree once severely poisoned in this way, for the soil is saturated with gas, the roots are killed, and it is practically impossible to renew the soil. Watering, which has been proposed as a remedy, does not seem to counteract the poison. If detected in time, renewal of the soil, root pruning, and severe cutting back may restore the patient. Electric Currents. The appearance of trees killed by gas is very much the same as that of those killed by light- ning or electric currents, the foliage dying and remaining hanging on the tree. This takes place not necessarily only on trees which show the lightning stroke along the trunk, but also as a result of general electric conditions of the atmosphere, or of a discharge through the whole tree, with- out any apparent actual mechanical injury. If the stroke follows a vertical line along one side of the 72 Diagnosing of Diseases bole there may not be any more consequences than accom- pany any ordinary or frost-split wound which may be healed by callusing, but when it follows a spiral course, killing cambium on all sides of the tree, the result is like that of girdling. Very lately it has been discovered and experimentally demonstrated ' that electric shocks of low tension occurring during thunder-storms, especially in winter, are the frequent cause of the phenomenon described above as staghead, the leader and upper portions of the crown for from five to ten feet or more being killed while the rest of the tree remains uninjured. Every tree owner should look out for the wire stringer, who not only disfigures the tree by chopping off branches, ‘regardless of consequences, but introduces the danger of electrocution. Trees and branches, beating against elec- tric wires'In winter storms, wear off the insulation and thus establish short circuits, which under certain weather condi- tions as, for example, in a thunder-storm, may bring about the total destruction of a long-cherished old tree. According to the latest investigations ? there is a difference in the effects of direct currents which are used chiefly in operating electric railroads, and of alternating currents of the electric light plants, which, although carrying a higher current, appear to be less disastrous. In moist or wet weather, when the tree is covered with a film of water, the current causes, at the point of contact, an injury to the tree, which provides favorable conditions for leakage through the film of water, grounding the current and burning the limb, partially or entirely killing the cambium 1See Forestry Quarterly, Feb., 1904. 2“Tnjuries to Shade trees from Electricity.” Bulletin No. 91, Mass. Agr. College. Light Conditions 73 at point of contact, and drying out the limb above. With alternating currents the damage seems usually confined to this local destruction at or near the point of contact as a result of the heat created. With direct currents, in addi- tion to these local burnings, electric effects are sometimes noted at a distance, the escaping current girdling trees at the base, and killing the cambium without the characteristic burning at point of contact or at point of discharge. This appears to happen only when the positive current is not as usually carried by the feed-wire, but by the rail, and leak- age through imperfect rail-connection occurs. In an ob- served case the damage was done when the trees were four feet from the rail, the moisture conditions of soil and bark being evidently most favorable for electric discharge. The only help is, of course, to string the wires outside of the tree line, or at least to prevent contact, keeping in mind that winds will sway the branches and that allowance must be made for this. No authentic cases of injury or death, due to the mere effect of the light of arc lamps, are on record. Light Conditions. Where trees are planted close to- gether, standing in groups or clumps, there is apt to be an uneven distribution of light, some trees or some parts of trees being deprived by their neighbors of a sufficiency in that respect. The light is necessary, as we have seen, for the leaf to perform its functions in assimilating food. Defi- ciency in this respect may show itself in ediolation, the leaves becoming small and elongated, and the leaf-stalks and branchlets thin and slender. Finally, when the shade becomes too dense, the shaded portions die. This very important observation is utilized by the forester in secur- ing branchless boles by the natural trimming that takes place in dense growths. 74 Diagnosing of Diseases It stands to reason that the stronger and more shade- enduring species, having also a denser crown, will retard the development and kill out the light-needing varieties that may have been planted under its shade. The sensi- tiveness to withdrawal of light increases with deficiency of soil moisture. Pruning back of the stronger will give the weaker a chance for development. Care is necessary, however, with some species, especially conifers, in not opening up too rapidly, so that the foliage may gradually adapt itself to the new light conditions. Wherever there are trees planted in groups or as close neighbors this relative shade endurance becomes one of the most important factors in influencing the form develop- ment of the tree, and where light-needing species are in competition with shade-enduring, the former are likely to lose the battle. Mechanical Injuries. Finally, if none of the causes of disease so far discussed can be adduced as occa- sioning abnormal conditions, we must look for mechanical injuries. As we have seen, mechanical injuries to the bark and wood, by whatever agency inflicted, are first of all injurious by admitting destructive fungi. In addition, the bark, branch, or bole being broken or torn off in places, much of the underlying cambium and young wood is killed and rendered inactive in conducting water and food materials. As a consequence, some parts of the crown and of the root system are underfed and suffer in proportion to the extent — of the injury, until the wound is healed and closed up. Usually, such injuries are one-sided and it is, therefore, a particular branch or one side of the tree which shows the influence of the under-feeding in the foliage or in dying portions. More regarding the nature and _ physiological Mechanical Injuries 75 influence of these injuries will be found in the discussion of their repair in the next chapter. It will hae become clear that the diagnosis of diseases in trees, although by no means as complicated as in the animal, nevertheless requires considerable knowledge and judgment. CHAPTER V CONTROL OF PHYSIOLOGICAL DISEASES AND TREATMENT OF MECHANICAL INJURIES — GENERAL CARE OF TREES ag;| UST as in all other cases, the ills to which trees are exposed are best met with the prescrip- tion of the old adage: “An ounce of prevention is worth a pound of cure.” Just as the physician insists upon sanitary conditions, as a means of preventing disease, so the tree doctor should insist upon securing the most favorable conditions of growth for his charges. ‘These may be achieved by looking after soil conditions, mainly with reference to air and water-sup- ply; by providing a satisfactory amount of light, and, above all, by timely and judicious surgery—pruning, by which the consumption of supplies from the root can be regulated sometimes more easily than the supply in the soil itself. These two means, then, regulation of foliage development by pruning and soil improvement, are compensating and should usually go hand in hand. ‘Timely attention to these requirements will prevent many of the troubles to which trees are liable, and, when trouble has come, half the battle is won, if these conditions of favorable nutrition are estab- lished and the tree has been kept in vigor to fight off the disease. We shall devote this chapter, therefore, entirely to the discussion of proper care in soil conditions and in pruning, 76 Soil Improvement 7G whereby physiological diseases are prevented or cured, and mechanical injuries rendered harmless. ‘Too much stress cannot be laid upon the need of such care. ‘Tree owners do not seem to realize that, after the plantation is made, it still requires attention; that most trees deteriorate or die because they are underfed and allowed to dry up. Sufficient water-supply is the most important means of maintaining healthy tree growth. . Soil Improvement. The most natural conditions for tree growth are found in the virgin forest: a soil continuously shaded, practically free from grass and weeds, covered with a heavy mulch of decaying foliage and of humus, which prevents evaporation and keeps the soil granular, easily penetrable to water and air, and well supplied with food materials. Street trees and lawn trees are not growing under natural conditions. In the one case the pavement keeps much of the water from penetrating, while in the case of the lawn, the grass competes severely with the tree for water, and the - natural mulch of foliage is raked off every year, and thus food materials and soil protection are removed and much moisture is allowed to evaporate. Such trees are, therefore, more or less on starvation rations; they show almost always that they are underfed, or else suffer in their respiration, and, if any other contributive cause for unhealthy condition is added, they readily succumb, espe- cially as they grow older and the difficulties of securing their water-supply increase with age. In lawns, therefore, and in streets, where practicable, the sod should be taken up from time to time, or the soil stirred so as to secure better aération, and a dressing of hardwood ashes, of garden mold or of well rotted stable manure applied, and possibly a mulch of spent bark shav- 78 General Care of Trees ings or leaves should be added. If this is done in the fall the tree will be invigorated with new life, the winter moist- ure will penetrate, and new rootlets will form in larger numbers, for root activity continues long after the fall of leaves. In the spring the sod may be re-established, although badly starved trees will be benefited by keeping them mulched for a few seasons. The mulch should not be too thick, just enough to prevent the pattering rain from compacting the soil, and to prevent evaporation from it; this may be attained by a cover not heavier than one-half to one inch. Nor should the mulch be allowed to become compacted itself, so as to impede free penetration of water and air. There is not much value in making this application close around the stem; it is under the trough of the outer foliage, under the ambitus of the crown, that the main feeding root- lets are located, and here the treatment will most benefit the patient. On shallow and very compact clay soils this treatment should be frequently repeated, and possibly at the same time some sand or garden mold should be worked into the soil, or else an application of lime, marl, or gypsum may be made, which has the effect of granulating a stiff soil, making it porous and thus improving its water-conducting capacity. The application of slacked lime, as free as possible from magnesia, should be made during the winter in small re- peated doses at the rate of about one to three pounds per hundred square feet. Watering, where practicable, will, of course, overcome the effects of drouth; but it must be kept in mind that a surplus of water may become injurious by reducing aéra- tion. Often, the mere loosening of the soil is sufficient to correct the deficiency in water-supply: the loose surface 6 Fertilizing 79 soil acts precisely like a mulch, the capillaries having been destroyed. Hence no water can rise from below into the surface layer, and thus loss of water by evaporation is pre- vented. In applying water to the surface, therefore, the compacting of the soil by the water must be avoided, and this is best done by applying the water through ditches or holes near the tree, by sub-surface watering. Where, due to soil and topographic conditions, continued excess of moisture is experienced, and aération thus im- peded, the drainage must be improved. Usually it is better simply to lower the water table than to attempt thorough draining. An open or covered ditch properly located at some distance will do the work. Such ditches may be filled up with rubble and then be again covered and sodded. It is, however, advisable to be very cautious in attempt- ing the regulation of the water-supply by drainage, for not only do species vary in their water requirements, but the individual trees, having once adapted themselves to a wet situation, may resent any sudden change of condition. Time must, therefore, be allowed the tree to adapt itself, by changing the water level gradually, while at the same time the process of adaptation may be assisted by judicious pruning. Fertilizing. Troubles due to deficiency in mineral salts in the soil are of rare occurrence, since most soils contain sufficient quantities of the needful minerals of which trees require only small amounts, their bodies being mainly built up from the carbon of the air. The only mineral likely to be deficient is nitrogen, the lack of which would produce a yellow or even whitish appearance of foliage. In nature this mineral is provided by the decay of fallen leaves, in which the nitrogen-gathering bacteria work. So the practice of raking off the leaves in parks is one way of starving trees. 80 General Care of Trees A nitrogenous fertilizer, or an occasional dressing with hardwood ashes, which contain the required minerals in most accessible form, is to be recommended wherever the vigor of the tree is impaired. A dressing of ten pounds of -ashes per hundred square feet, costing perhaps. twenty cents, will be found very ample. Although in most cases hardwood ashes are as good a fertilizer as need be, for very impoverished soils the follow- ing mixture will be found serviceable and should be applied ‘in early spring before the leaves unfold, namely, one pound of nitrate of soda, five pounds cotton-seed meal, two pounds acid phosphate, two pounds muriate of potash, the whole mixed together just before using; one pound of this mixture costing, if prepared in quantity, less than two cents per pound, will suffice for a hundred square feet. This is also an excellent top dressing for lawns. | The growing of a crop of clover, alfalfa, lupine, or some other similar crop and plowing it under while green, is also an excellent means of recuperating impoverished soil both physically and chemically, and at the same time improving its aération. While lawns are benefited by sheep, cow, and horse ma- nure, and some flowering shrubs respond to treatmentewith a compost made of bone dust and manure, or better still, with leaf-mold, the physical improvement of the soil for water conduction by stirring and mulching, as advised in the preceding pages, is usually all sufficient for arborescent growth. Points in Grading. One of the most common mistakes causing the loss of many old trees, is the filling up of ground over the roots in grading operations, by which water and still more surely the necessary air is excluded. This careless burying of the roots shows inexcusable ignorance Points in Grading 81 of the requirements of tree life, for if the cover is of sufficient depth, say two feet or more, and especially if of compact soil, it will usually quickly and surely kill the tree. No less ignorance is exhibited by those who, when such filling is to be done, leave an unfilled depression or space directly around the bole, perhaps walling it up with brick and covering with wire netting or filling with rubble. In doing this the notion is to admit rain water, and perhaps also air, to the roots. But, while undoubtedly the admis- sion of water and air is facilitated by this device, the need of water and air is much less near the bole where only con- ducting roots are located, than on or towards the ambitus of the crown, where the feeding rootlets lie and the respira- tion is most actively needed. Filling around the bole is, to be sure, undesirable as it not only clogs respiration in that part of the bole, but, with some species, induces the formation of suckers, which weaken the tree. Hence the precaution of keeping the base of the bole free is a good one, but it does not compensate for the filling over the feeding rootlets. There are three ways of meeting the trouble, if there is a strong desire to save the trees instead of removing and replacing them by others. Where practicable, the filling should be done so as to leave depressions with gentle slopes towards the feeding area of the root system; or better still, the filling should be done gradually, taking if possible several years, and after first thoroughly stirring and fertiliz- ing the ground around the roots, so that the tree may wake new feeding roots towards the surface. Or, where deep fillings have to be made and valuable trees are to be saved, the following device may be employed. After the ground has been stirred and fertilized as suggested, an air chamber may be established by covering the ground 82 General Care of Trees with rubble or broken stone before putting down earth and sod, keeping the space around the bole open and in addition introducing through the filled ground aérating pipes which connect the air chamber with the outer air. In any case, trees so treated should be at the same time severely pruned, since some of the feeding roots are bound to die and it is necessary to establish an equilibrium between root system and crown system. Otherwise nature will do the pruning and perhaps not in the manner desired. Different species vary in their sensitiveness to the with- drawal of air and, as we have seen before, trees which have grown up in swampy conditions make provision in other ways to meet their requirements for air, and may therefore be covered to a considerable extent with impunity. In general it will be found that the trees naturally growing in the swamp will stand filling best. The depth and character of the soil used for cover will naturally also have to be considered, since with a loose soil and a moderate depth the respiration may not be materially interfered with, while a thinner layer of clay would be detrimental. In most cases, however, the safer way is either to avoid the grading or to replace with new trees. Whenever it becomes necessary in grading, making of streets, laying of conduits, etc., to cut into and destroy part of the root system, a corresponding amount of the crown system should be removed by proper pruning, keeping in mind the fact that the side on which the roots are destroyed is the one that needs to be most severely pruned. The aération and watering of street trees is a most difficult question, especially where macadam or other solid pavement is used. It is, therefore, necessary in the first place to choose species which are frugal in that respect. Here again, species Pruning and Trimming 83 growing naturally in the swamp promise well. In addi- tion, a certain space, say one and one-half by two yards, should, if practicable, be left unpaved around the base of the tree, and this space should be kept open, stirred and fertilized from time to time. Where this is not practicable, a smaller space left unpaved may be covered by a grill or iron grating, supported on wooden pegs driven in the ground. Such grills are found in Paris, Berlin, and London (see page 119), and permit of watering the trees. This treat- ment is, to be sure, applicable only with new plantings, when the trees will adapt themselves to the conditions. Where old established trees are concerned, it is doubtful whether they can be permanently maintained when a tight pavement is placed over their roots. Pruning and Trimming. Next in importance to atten- tion to soil conditions, there is nothing of more value for avoiding and correcting trouble in tree economy than prop- erly applied surgery. There is competition everywhere in the living world, and not only do the individual trees compete with each other for root and air space, water and light, but each leaf, each bud, each shoot competes with its neighbor, although only a limited number can develop. As we have seen, trees prune themselves, 7.e., some of the buds and branchlets die every year and are broken off by the wind. This natural pruning is the result of the struggle for existence, 7.e., for food and light supply, between the buds or branchlets, and an adjustment in the economy of the tree, keeping the balance between income and expend- iture. By reducing the number of mouths to be fed the remaining are better fed. There is, therefore, not neces- sarily any apprehension to be had if some twigs and branches die in response to the perfectly normal need of adjusting 84 General Care of Trees consumption to nutrition and light supply. On the contrary, by anticipating this natural process through timely artificial pruning and trimming, still further advantage can be secured; for, by interfering early and limiting the competition, the vitality of the remaining branches is increased, so that pruning acts very much like soil improvement. The common practice in pruning is to cut out the dead wood; the proper practice is to prune in time so as to avoid as much as possible the making of dead wood. By judicious and systematic trimming (heading in), both the form and the health of the trees are improved, and in fruit trees even the fruit-bearing can be influenced, — but this is an art by itself. Such trim- ming should be done annually or biennially, when only small tess: cee a for changes at a time are made, the ; branchlets cut are small, and the tree economy is only slightly disturbed. The branch system being kept shortened, the roots are much more likely to suffice in supplying the needed water even in drouthy seasons, while enough dormant buds will develop to fill out the crown as much as is needful. Thus by timely and systematic attention we can produce just such forms and conditions in a tree as we desire, instead of leaving it to the accident of natural development. Indeed, in such light-needing species as the Sycamore or Silver Maple, which are apt to thin out in the interior of their crown, the crown may be considerably improved and the foliage cover thickened by such cutting back of branches and consequent formation of new branchlets, which fill out the otherwise thin crown. Another advantage of cutting “or heading back” the annual shoots in rapid growing Pruning and Trimming 85 trees with sprawling branch systems, as in the case of the Soft Maple, is to make the crown more compact and thereby to increase its resistance to wind breakage. Unless this operation is judi- ciously performed there is danger of spoiling the natural form and making the crown formal and undesirable. Fic. 14. — Levin’s patent pruning shears. Whenever twigs or branches are dying without a visible cause, it is in many, if not in most cases a sign that the root and branch systems are not in equilibrium, and it is SS: ao en SSS SS = ae Itc. 15.— Broken branches which have not been pruned, liable to intro- duce rot. proper to remove not only the dead wood, but also some of the green wood, in order to give the root system opportunity to do its work more easily. How severely this surgery may be applied depends on the condition of the individual, the species, and the age. Some species, even when quite old, respond more readily to the treatment than others, and they may be cut back severely into old parts and yet rehabilitate themselves. Others, like the ash, do not respond so readily and lose, as does also the oak in very old age, the power of re- placement by dormant buds. Per- haps it may be a law that all those that sprout readily from the stump, such as the oak (when young), chestnut, basswood, and maple, also respond readily to the pruning knife. 86 General Care of Trees Besides the trimming for form and equilibrium, all broken branches must be at once pruned in proper manner, to pre- vent location of fungus spores, for, as we have seen, branch stumps are the most prolific causes for the beginning of rot. The rules for proper pruning, although simple and based on a knowledge of tree physi- ology, seem most generally un- known or overlooked, because Fic. 16.— Solid steel pruning the operation is left to ignorant shears. . workmen. There is_ probably more loss of tree life due to unskilful pruning than to any other cause. Nothing can more pithily and impressively express the public attitude still prevailing to a large extent on this subject than Lowell’s words in a letter directed to the Presi- dent of Harvard University in 1863, a letter containing so much common sense on tree management that we quote fully from it. “Something ought to be done about the trees in the col- lege yard. . . . They remind me always of a young author’s first volume of poems. There are too many of ’em and too many of one kind. If they were not planted in such formal rows, they would typify very well John Bull’s notion of ‘our democracy’ where every tree is its neighbor’s enemy and all turn out scrubs in the end, because none can develop fairly. ... 1 think Hesiod (who knew something of country matters) was clearly right in his ‘half being better than the whole,’ and nowhere more so than in the matter of trees. . . . We want to learn that one fine tree is worth more than any mob of second-rate ones. We want to take a leaf out of Chaucer’s book and understand that in a stately grove every tree must ‘stand well from his fellow apart.’ . Manner of Operation 87 Nor should the pruning as now be trusted to men who get all they cut off, and whose whole notion of pruning, accord- ingly, is ‘ax and it shall be given unto you.’ Do pray take this matter into your hands — for you know how to love a tree — and give us a modern instance of a wise saw.” Manner of Operation. \ie may distinguish between trimming or heading in, which refers to cutting back or shortening of twigs and small branchlets with shear or knife, and pruning proper, which refers to operations with axe and saw in removing larger branches. It is in these latter operations that care is most needful, in order to avoid secondary damage from fungus disease. The tools must be sharp; the saw with wide set for large branches; the cut must be made smooth. When cutting heavy long branches there is danger of the weight of the branch breaking it off before the cut is completed, splitting, splintering, and tearing off bark. _ To avoid this, two cuts should be made, the one at some dis- tance, —two or three feet — from the base of the branch, to relieve the leverage, the other, 5, 17 Mettiod of tenouine which is the final one, or near 4 heavy branch without split- : ting and tearing the bark on the final one, at the base; in the under side, the lower notch both cases first sawing a kerf or eins made first. notching from below half way through the branch, and then sawing or notching from above, in order to avoid splitting and tearing off bark on the lower side. With very large branches or tops to be removed, mechan- ical appliances, such as chains and ropes, varying with conditions to suit the case, for the purpose of avoiding 88 General Care of Trees damage will readily suggest themselves. A rope or hook ladder will often be a desirable addition to the outfit. Where saw or axe cannot readily be used, a chisel and mallet may be substituted. In any case, a smooth surface must be secured, not a hacked and lacerated wound. Always cut close at the very base of the branch to be amputated, with a cut as nearly parallel to and even with the outline of the main axis (branch or trunk) as possible, ks —— = Fic. 18. — Good and bad pruning. A, side view of good and bad branch pruning; B, front view of a well pruned branch. leaving no portion or stub of the amputated dead branch on the trunk. Many older branches as well as younger, have at their base a swelling bulge, sometimes called a “‘shoulder’’; this must be cut into and removed in order to satisfy the-requirement of close cutting, in spite of the fact that the wound is thereby greatly enlarged. The object of cutting close and parallel to the remaining axis Is to expedite the closing of the wound by the callus or wound wood formed from the cambium at the margin, which, as we will presently see, is more readily formed when the cut is made as prescribed. Great care must be Manner of Operation 89 taken not to loosen or separate the bark from the wood at the margin of the wound, or to crush the cambium in this region. All wounds must: be smoothed and then heavily dressed with an antiseptic, impenetrable cover, in order to keep out water, and with it, bacteria and fungi. Common lead paint answers this purpose best, being antiseptic as well as lastingly impenetrable to Fic. 19. — Topping shears. water. By making it as nearly as possible the same color as the bark the unsightliness is reduced. Coal tar is also recommended, but aside from its unsightly color it sometimes damages the cambium at the edges, and is not as easily handled as lead paint. Be sure to make the coating thorough, possibly applying two or three coats. This coating or dressing does not influence the healing process in any way, but is merely a mechanical device to keep out water and fungus spores. Therefore, every cranny should be filled, especially the lower edge, which collects water more easily. If cracks appear, the coating must, be renewed so as to fill them and keep out the surface waters. With the observation of these few simple rules, any intel- ligent man can do the ordinary pruning without doing dam- age. As to the time of pruning, there are advantages and dis- advantages in every season, although the operation may be performed at any time with safety, provided it is properly executed. During the early growing season, when the bark peels easily, there is greater danger of injuring the tree mechanically by bruising the bark; so it is better to defer the pruning until fall, winter, or very early spring. In > go General Care of Trees summer the leaves are also a hindrance to the work, and, besides, a certain amount of food in leaves and young parts would be lost to the tree, endangering the life of a propor- tionate number of rootlets, or at least unnecessarily reduc- ing the reserve stores. Light trimming, however, may usually be done in summer with impunity. For pruning into live parts it is better to wait until the foliage has withered, when the food contents of the leaves have been withdrawn into the trunk and become available for the unfolding of the next year’s buds. The cold winter makes prun- ing an uncomfortable operation, and the results are therefore hazardous and less efficient. It is, in addition, physiologically undesirable, except on mild days, as, owing to the uneven expansion of bark and wood under the influence of frost, the wood is apt to shrink away from the bark, and a consider- able portion of the cambium may be killed, rendering the healing process more difficult. For the choice of early spring (March or April) it is said that then the healing process of the wounds sets in at once, or at least sooner than when made in the fall, and the dan- ger of fungus infection is reduced. But as a matter of fact it is generally believed that the season has not any appreciable influence on the healing of the wound, provided the pruning is properly done, which means also proper protection of the wound. Large wounds especially are best made in fall or early winter (October, November, and December in the Northern States) rather than in spring. In winter the bark adheres firmly and the wood is dry so that the paint or tar can be more readily Fic. 20. — English shears. Callusing and Repairing g1 applied, while in spring the oozing sap of many species will prevent the paint from sticking or the tar from penetrating. If pruned in the fall, the wound wood begins to form in the early spring and is well advanced before the fungus spores begin to fly. ‘The com- parative absence of fungus spores in late fall and the fact tat the form of the tree is better visible when the foliage Fic. 21.— Malleable pruning has left it also favors this season anos as compared with the summer. Orly those species, which, like the maples and birches, are apt to bleed freely even late in the autumn and early in spring, are best pruned in winter or late summer, although the bleeding is in the ' main detrimental only because it prevents the paint from adhering. Callusing and Repairing. We will now briefly look at the healing process, a knowledge of which will be useful to the pruner and will assist his judgment, especially as to where and how to locate most advantageously the cut in trimming, pruning, and repairing. When, in the natural order of things, a leaf falls, or a piece of bark is sloughed off, as is so conspicuously done in the sycamore, this loss of parts has been gradually prepared for and the wound is already cov- ered securely by a cork layer, or Ne: ae See shearing 4 temporary covering has at least been provided for by the formation of gum or resin, before this final voluntary loss occurs. When an involuntary physical injury, as the tearing off of a piece of live bark or the breaking of a branch, takes place, a similar process of providing a covering of the wound 92 General Care of Trees sets in, but this takes time, and meanwhile the exposed part is subject to inimical influences, drying out, or giving access to parasites. Of course, only so far as living tissues are touched or exposed is there any real injury, hence scraping or breaking off the dead outer bark does no direct harm and the cutting off of dead branches in the dead parts produces no further results. When live tissues have been injured, a certain area of the wounded and exposed live tissues dries out and dies before the healing process has begun, and it is only by the growth of neighboring live tissue that a covering can be gradually established. In other words, the cut surface or wound consisting of dead tissues cannot heal over as a flesh wound does, but the narrow ring of cambium cells at the margin of the wound, being relieved from the pressure of the bark, subdivides and grows rapidly; and an excessive growth of wood cells and bark cells takes place, forming the so-called callus or wound wood, and this protrudes from the old bark over the wound, like a thick mass boiling over from the rim of a vessel. Year after year it increases in mass, and finally covers up the surface mechanically, leaving only a scar where the margins meet; and in time even this may vanish. The wound, then, is not really healed; merely a mechanical cover or cap is established, not organ- ically connected with the surface of the wound, and, if properly cut, it comes off like the cover of a box. In conifers, especially in young trees, usually an exuda- tion of resin first covers the wound, preventing loss of water and entrance of fungi, but the callus itself forms more slowly, and in older trees both processes of resin and callus forma- tion may become feeble or fail altogether, so that careful attention to the wounds is necessary. The growth of the callus, like all other growth, takes Callusing and Repairing 93 place, of course, during the growing season only, and is due to division and enlargement of cambium cells into wood, cork, or bark cells. Since these cells preferably divide ver- tically or lengthwise, and since the assimilated food materials required in their growth are carried from the foliage down- ward, the upper edges and the sides of the wound usually close more rapidly than the , lower edges. F For the same reasons, a branch stub protruding from the trunk or larger branch SS heals more slowly, for here yy! cee ; 447) the cells must divide hori- Yj, mir h zontally or crosswise, which CDRS they do with difficulty; more- my over, the cells, being out of i A 153 the direct path between root and foliage, have to derive their food materials circui- Fic. Satisfactory growth of the ao 23. callus over a pruned branch. tously from a _ neighboring branch, and are apt to find them less in quantity and less readily available than if a direct supply from the foliage of its own lost portion could have been had. Hence a vertical wound, running up or down the trunk or branch, is much less dangerous and more quickly covered than a much smaller wound running around the bole or branch, and similarly, the wound made by the loss of a branch at its very base is more rapidly closed than when cut or broken above the base and across the diameter. Branch stubs are, therefore, apt to die back and to decay most readily, because longer exposed to the action of rot fungi without any vital process counteracting these fungi. In the case of small branchlets or twigs, which have been Fic. 24. — Callusing proceeding from the sides, not the top or base of the wound. 94 Callusing and Repairing 95 trimmed back, if the wound is not covered at once with wax — which keeps it moist and the cambium layer at the circumference active, so that it can form a callus under the wax — the twig dries out and dies back for a shorter or longer space. The cambium below the dead portion will, of course, seek to repair the damage, and its activity will make itself apparent in a bulge of the bark, and when the dead stump has broken off, the callus will proceed, as described above, to cover the ragged wound. More frequently and prefer- ably, a bud below the dead pertion will start into life and grow into a shoot; the shoot will tend to take the direction of the mother branch and by its growth at the base will expedite the sloughing off of the dead por- tion; in this way the wound is . Fic. 25. — A bud below the ter- covered more rapidly and com- minal branch starting into ac- pletely than by the ordinary pace to supplant the lost callusing process. Thus in a short time its existence is only to be inferred by a crook in the branch; and eventually even this crook may be outgrown. Hence in trimming back, care should be taken to cut near to a strong bud or branch, and yet not near enough to have the bud itself dry out or be injured. What should be the distance of the bud from the wound depends on a vari- ety of conditions, which influence the rapidity and intensity of the drying out of the stub. If cut in the spring, shortly before or after the activity of the buds has begun, the cut 96 General Care of Trees may be made quite close to the bud; if earlier, it will be safer to leave a stub of a quarter to a half inch in length. Or the stub may be left an inch or more at first cutting, and after the bud has started, the stub may be cut back to near the base of the new shoot. The rapidity with which wounds, especially large ones, are covered up by callus for- mation depends on various conditions. Different species behave differently in this re- spect, but finally the general vigor of the plant, its age and its condition of nutrition, 1.e., the amount of food ma- terials it can elaborate, de- termine the rate of progress. The size and number of the wounds, their smoothness or y roughness, their location on Fic. 26. — Correct method of trim- the bole. whether or not a ) ming, a stub being left one-quarter a to one-half an inch above the next Stump has been improperly eau ts left and what its length is all these facts have an influence; indeed, conditions are so variable that it is impossible to give definite rules, save in a given case, as to how severe the pruning may be. If, however, the wounds have been properly dressed and ket covered against water and fungi, it does not matter how long it may take them to close, although the danger of the deterioration of the antiseptic covering naturally increases with time. Small wounds are covered relatively much more quickly Callusing and Repairing 97 than large ones. ‘The proper practice is, therefore, to prune in time, so as to avoid the cutting of large branches. In order to secure a satisfactory proportion be- tween the amount of food material used in making callus, and the supply, it is best not to make too many large wounds at once, and, if possible, no wounds larger than four to six inches in diame- ter. Three medium-sized branches of from three to four inches in diameter may be safely removed in any one year, even from old trees, and the wounds will heal in from three Fic. 27.— An example of proper prun- =a se years, while young ing, but with the wound left undressed. vigorous trees will elaborate enough food material to take care of a larger number. The wounds on young trees and in the younger portions of the trees heal more readily than those on old trees and those near the base, removed from the food-elaborating foli- age. In very old trees which are underfed, the callusing pro- Ric. 28. — Imported bill hook. egg may go on with exceeding slowness or may even be entirely suppressed. Wounds on the lower side, shedding water more readily, are less dangerous than those on the upper side of limbs. In general, the fewer and the smaller in extent the wounds 98 General Care of Trees and the more they lie in the length direction of the stem, the more readily are they covered; 7.e., the more live cam- bium borders them sideways, the more active the foliage above the wound, and the more directly the repairing cam- bium is fed. The severity with which a tree may be pruned depends, then, mainly on its capacity to cover the wounds in a reason- able time; and since this is a result of food elaboration, it depends on the growth conditions of the tree. Therefore, the tree surgeon, like the surgeon in the hospital, must consider the condition of the patient. The pruning may be executed in the most careful and approved manner, and yet the result may be disastrous if the vitality of the tree is not equal to the task of repair. If the pruning were accom- panied by attention to the vigor of the tree in improving its chances for nutrition, results would more often be satis- factory. Hence, if you prune heavily, do what you would expect to do with a human being that has an operation to undergo; make it comfortable and keep it well fed in order to invigorate its constitution. Specific Rules. Pruning of ornamental and shade trees is practised, then, (1) to remove superfluous and injurious parts, (2) to keep the trees within manageable shape and limits, (3) to train the tree to desirable form, (4) to modify the vigor of the tree. Pruning for Balance. ‘The first pruning is to be done at the time of planting, when it is needful to restore the balance between the branch system and the root system, the latter often having been curtailed in the operation of transplanting the tree. First, all injured roots need attention. Broken ones must be cut with a sharp, smooth draw cut, in such a manner that the face is on the lower side, so that from it Pruning for Balance 99 new fibrils may form in the natural direction. Bruised roots, if too much lacerated to promise ready healing, are also better removed, since they may otherwise become starting points for rot. If they cannot be dispensed with without too much loss to the tree their treatment may fol- low the prescription for treat- ing wounds in general (see page 89). Next comes the trimming back of the head to balance with the root system, keeping in mind in the choice of parts to be removed the height from the ground at which it is desired to start the crown. Injured or misshapen parts are, of course, the first to be subjected to the knife. Next a heading in of the tips of spindling branches may suffice, with due reference to desir- able shape of the crown. Finally, if this seems insufficient, whole branches may be entirely removed by cutting them out close to the stem. When it seems undesirable to use the knife, the balance may be attained by breaking out buds, and this is the preferable method, especially in conifers, as the knife is apt to spoil their form. If, in the planted tree, balance between the root system and crown system has been disturbed, as may be occasioned by the loss of roots through grading, the same operation of balancing the crown is needed, always keeping in mind that the tree will, unaided, restore the balance, but without reference to its appearance; hence it is desirable to anticipate the natural process. The need of pruning for balance when part of the root Fic. 2g. — Pruning axe. Fic. 30. — Brush axe. 100 General Care of Trees system is killed by winter cold has been discussed on page 67, where injuries by frost are described. Pruning for Form. The removal of dead and broken branches and the smoothing and proper dressing of badly made wounds is, of course, the first concern of the pruner. The removal of green branches has usually for its object the regulation of the form, in order to favor invigoration, or new formation in other parts. Every branch or twig cut produces a change in the development of other branches or twigs, because these now enjoy different light, food, and water- supply. The skilful pruner keeps in mind, therefore, what new develop- ment will be induced by cutting away branches, and cuts accordingly, either to strengthen a weaker mem- ber by removal of a stronger, or to , help a stronger one by subduing Fic. 31. — “Lightning 2 : double edged pruning superfluous feeders, favoring either Saw. the leaders by the removal of side branches, or inducing the spread and compacting of the crown by heading back the leaders. And, in pruning for form, he keeps in mind that the heading in of young shoots tends to develop dormant buds; that the tendency of most species is to develop the uppermost buds rather than those . at the base of the shoot; that heavy pruning at the top tends to invigorate and produce better development of the lower portions, and vice versa. Of superfluous parts to be removed are the water-sprouts or suckers, for, as their very name indicates, they are rob- bing other branches of food materials. Water-sprouts are branchlets, arising from adventitious buds out of regular Pruning for Form 101 order, along the trunk and branches, whenever the equilib- rium in feeding conditions is disturbed and has to be ad- justed, as, for instance, when the tree has been heavily pruned, or when soil or light conditions have been changed. Although they are not neces- sarily a detriment, it is evident that they interfere with the development of the regular crown and are therefore best removed. It appears that water-sprouts are less likely Fic. 32. — An example of correct to form if the pruning is done _ pruning, well healed, but with : water-sprouts developing. after midsummer, when a re- adjustment of feeding conditions without this expedient seems to take place. In setting new trees, or in the case of plant material which has not been trained in the nursery to form its head at a desirable height from the ground, this should be attended to first. This height depends upon the species and the object for which the planting is done. In specimen trees, and especially trees of high stature, and decidedly in conifers, the crown should reach down almost to the ground. In shade and street trees it is desirable to keep it from ten to fifteen feet above ground. In street trees and in ornamental plantings, where several kinds of trees stand close to each other, the pruning knife may be used to advantage in preventing an undue expansion of crown. If this is done at regular and not too long intervals, interference between neighboring trees and the conse- quent influence on each other’s form may be avoided and the operation be kept within the limits of a slight trimming back. 102 General Care of Trees In planted groups of several species, the fact (referred to on pages 25 and 73) must be keptin mind that the different species vary in regard to the amount of light which they require for normal development. Some, such as the Beech, Maple, and Holly, are very shade-enduring and at the same time they themselves make a dense shade; if associated with such light-needing species as the Tulip tree, the Ash, Walnut, Cherry, and many others, the latter will be ¢ at a great disadvantage: the shady species Fic. 33.— “ Tele- j : ‘ graph” tree crowding them, suppressing their branches, ae oe and possibly shading out the entire tree, unless the shaders are kept within bounds. The pruner must study these relationships, must protect the weaker, and must give them at least a free upper crown, if he desires to keep the groups in harmonious development. A little observation will soon show which trees are relatively weaker in their shade endurance. The most difficult task of the pruner, because requiring the most judgment, a sense of fitness, and a clear concep- tion of the results of his pruning, is that of training trees to desirable outline. This refers, of course, to single trees on the lawn, where the form and outline of the crown are the important features. The “natural,” symmetrical form, typical of the particular species, is, to be sure, the ideal one to be attempted in general. But it is by no means certain that the individual tree will, if left alone, develop this form. Not only do conditions of the soil, which influ- ence the root development, find expression in the shape of the crown, leading to irregular and sometimes undesirable Fic. 34. — ‘‘Paragon”’ double edged pruning saw. Pruning for Form 103 shape, but accidents, like breakages of branches, disturb the normal development and call for the correcting hand of man. Some species, as, for example, the Silver Maple, the Sycamore, and poplars, have a straggling habit, developing so irregularly, that their long branches are apt to be broken by the winds. By judicious pruning this habit can be counteracted, and the crown be made more compact and wind-resistant. Too often old neglected trees have lost their beauty by neglect in earlier pruning, and it may tax the ingenuity and good judgment of the tree doctor to restore them to desirable shape in order to save the time which their replacement would require. Usually in such cases general repairing and invigorating of the dilapidated cripples are also involved. As regards the form in which to trim a tree, it is neces- sary to know, not only that the various species exhibit vari- ous forms typical of themselves, but also that their form varies with age, the young tree being different in form from the mid- __ F'6- 35-— Plain one edged A : Fae pruning saw. dle-aged, and this again differing from the old tree. It is, therefore, impossible to give general rules; only study and observation in the field can develop the eye which recognizes typical form. There are, however, two very clearly distinguishable types, namely, that of the conifers, and that of most of the broad-leaved trees. The conifer type is characterized by the pyramidal shape of the crown, the main axis developing more rapidly than the branches, and these besetting the bole to its base. This beautifully symmetrical pyramid, which is especially typical of spruces and firs, lasts from twenty to forty years and 104 General Care of Trees sometimes even longer. Then the lower branches begin to die, and, when the tree has reached its full height, this loss of lower branches proceeds more rapidly, and a period of unsightliness must be passed through. Meanwhile, the branches of the upper crown lengthen and the crown broadens, the old trees of most species having a very differ- ent shape from the younger ones. It is, of course, desirable to retain the pyramidal form of the conifers as long as possible, to trim as little as possible, and then always to a strong lower bud, which will then ap- parently continue the limb as if Fic. 36.— California bow from an end-bud. The pruning shaped pruning saw. Z of lower branches, the peculiar beauty of the conifers, should be deferred until it becomes absolutely necessary. In conifers, bud pruning is advantageously practised to preserve perfect shape and prevent undue spreading. This is done by clipping off the center-buds from any shoot that projects beyond proper limits. This method will also tend | to improve and compact the form of such looser crown structures as the upright junipers. Should a leader be damaged or broken, cut it back, leav- ing a short stub above some strong branch, and tie the latter up (by using the stub) as nearly as may be into ver- tical position, when it will by and by assume the leader- ship and eventually supplant the lost one. “In the broad-leaved trees the tendency with most species is to lose the juvenile form, in which the main axis is prom- inent, sooner than in conifers; the branches develop more stoutly and the crown spreads earlier, unless by crowding in the forest or in planted groups, this spread is prevented and the shaft forced to grow upward. Pruning for Form 105 In the development from youth to old age there can be recognized at least four stages of development, in which the form varies. In 1864 a Frenchman, M. A. Des Cars, published a book- let on the methods of pruning trees,’ which is still essentially correct. It was written for forest- ers, with a view to secure the pro- duction of good timber rather than for use in ornamental trees. The author develops what he ee ane anaes considers the proper form for trees, especially oak trees, in the different stages of their development. He also devises what he calls a dendro- scope, a piece of thin cardboard, in which a hole has been cut of the shape which the outline of the tree crown is to assume. A fine wire, stretched from base to top of the whole, serves as a guide in adjusting the dendroscope oppo- site the bole of the tree in front of the eye. By this little device the pruner is aided in determining what branches to remove in order to secure the desired symmetrical form. While we would hardly recommend any strict adherence to the directions given on this point by Des Cars, we reproduce for their suggestivenéss the summary of his conclusions, together with the dendroscope and the examples of how to shape a given tree. The use of this device is self-evident. 1. YOUNG TREE. The length of the branchless trunk should equal one-third of the entire height of the tree. The head should be elongated, ovoid in form, with the center of gravity sufficiently low to keep the tree upright. The lower branches, shortened to prevent excessive development of the 1A Treatise on Pruning Forest and Ornamental Trees, by A. Des Cars. Translated from the Seventh French Edition, with an Introduction by Chas. S. Sargent, Boston, 1884. 106 General Care of Trees leader, should afford sufficient leaf surface to elaborate the sap necessary to insure rapid growth. 2. Mippie-AGeD Tree. The trunk should equal about two-fifths of.the entire height of the tree. The head should be a shorter ovoid than that recommended for trees of the first class. A vertical branch upright on the trunk, or any part of the trunk, should if necessary be made to replace the original leader; all other vertical branches should be shortened to encourage the growth of the leader. If a single branch cannot be converted into a leader, a regular well-balanced head may be made with several branches. As the tree grows some of the lower branches should be removed to increase the length of the trunk. Not more than three or four branches should be removed in any one year. The amputation of a branch should be carefully performed; the cut should be made perfectly smooth and rounded, to coincide with the form of the trunk, thus bring- ing its whole circumference into direct communication with the leaves by means of the layer of living cells. These distribute the descending sap, which alone forms the new wood destined in time to cover over the wound. Wounds made in this manner heal in a short time; but, to preserve them from external influences which induce decay, they should be covered as soon as made with a coat of coal-tar. All dead or dying branches, and all stumps of branches, should be cut off, and the wounds treated in the same manner. -3. Op Tree. The length of the trunk should nearly equal one-half the entire height of the tree. All decayed portions of the tree should be carefully removed.