Trees and their nature; or, The bud and its attributes: in a series of letters to his sons

Front matter

LETTERS ON TEEES.

TREES AND THEIR NATURE ;

OR,

Preface

The view given in tliese Letters of the nature of Trees^ although, in the main at least, the same as that first set forth by De la Hire, as long ago as 1708, and subsequently held by Darwin, Mirbel, Du Petit-Thouars, Gaudichaud, and others, differs widely from that commonly received among us. It neither represents the popular belief, nor does it accord with the recognised doctrines of the schools. To the popular mind, indeed, it may be said to be nearly unknown, while heretofore it has failed to secure the sanction of the greater number of our scientific botanists.

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PREFACE.

So little^ indeedj has the theory been countenanced by botanists, that, to take Professor Balfour's excellent Class-Booh of Botany (one of the fullest and most recent of our systematic treatises), as a fair exponent of the received doctrines in vegetable physiology, it may be questioned whether the notice there taken of the theory would lead any ordinary reader to do more than bestow upon it a passing regard, or would suggest to him the application here made of it (and obvious in itself) to two practical questions respecting trees — questions often put, and commonly felt to be exceedingly perplexing, viz., To what age do they naturally live?" and, To what size do they naturally attain?" Certain it is, that in considering these questions. Professor Balfour himself makes no allusion to the theory, and seeks for a solution of them in a direction altogether different from that in which it points.

It is precisely because our prevailing notions, both popular and scientific, differ so widely from what the author believes to be the truth on this subject, that he is induced to publish this volume. He is himself

PREFACE.

ix so convinced of the soundness of the theory which he advocates^ that he feels persuaded that all that is needed to secure for it a ready and general acceptance, is to lay both the theory itself and the evidence in support of it^ fully and clearly before the mind. Thisj he ventures to submit^ has not yet been done ; and to this circumstance he would attribute the position which the theory at present holds. It appears to him^ thatj while^ on the one hand, some supporters of the theory have advanced arguments in its behalf which are really untenable, so, on the other hand, some of its opponents have erroneously imagined that they had disproved the theory when they had merely shewn the fallacy of those arguments. It appears to him, likewise, that in respect both of the arguments in support of it and of the arguments in opposition to it, too much has been made of considerations connected with the wood^ and too little of considerations connected with the hud. The former, indeed, seem to him extremely valuable, and he has taken full advantage of them in his argument. Yet it is rather on the latter that he would rest the theory. The in-

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ferences to be drawn in support of it, from the nature and attributes of tbe bud^ seem to him so unassailable and so convincing^ that^ although he does not imagine thatj in the exposition here given of them, he shall succeed in carrying conviction to the mind of every one of his readers, he is not without a confident expectation, that among all classes of these, both the learned and the unlearned, the contents will greatly out-number the non-contents.

Although continually spoken of in these Letters as his own theory, the author begs to disclaim all pretensions on the score of originality. He has advanced nothing that was not known or held before. The only merit he is disposed to claim in connexion with it is, that of having unfolded it more systematically, and in greater detail, than any of his predecessors. At the same time, he thinks it due to himself to state, that it was worked out by him, substantially as it now appears, without any assistance from others ; that it was embodied in the course of Lectures on Physiology, which he delivered in Marischal College during the winter session of 1844, without any recollection

PREFACE.

xi at the time of the views of M. Du Petit-Thouars ; and that it was subsequently more largely developed in a paper On the Nature^ Longevity ^ and Size of Trees^ which he published in the Edinburgh New Philosophical Journal" for January 1847, long before he had any knowledge of the writings of De la Hire, Darwin, Mirbel, or Gaudichaud.

What led the author to direct his attention to this subject was, a difficulty he felt soon after he began his labours as a teacher of Physiology in 1840, in bringing trees within the pale of two laws universally regarded as applicable to all living beings — the law of a determinate duration of life, and the law of a determinate size of organism. His earlier inquiries disposed him to regard the difficulty as insuperable, and the laws as so far exceptional. After a time, however, two things drew him into the train of thought out of which the theory sprang. One was, reflection on the potato-plant as the produce of a stem furnished with hiids^ and capable of being reproduced from year to year indefinitely from buds alone, and the comparison of this with the results of

PREFACE.

slipping and grafting in tliose trees that admit of being propagated in that way. The other waSj reflection on the entire absence in all vegetables of anything corresponding to the renewal of substaiice^ which is constantly going on in the living tissues of animals^ and by which alone their continued vitality is maintained. Once in possession of these two keys^ the whole theory^ as here unfolded^ gradnally, and without any sensible effort, took shape in his mind. The difficulty referred to vanished^ and the lawSj imagined to be exceptional, stood out in their character of universality.

Trees being in themselves objects of universal interest — of interest even to the young, the author, while he has made it his first aim to treat his subject in a scientific spirit, has yet striven also to present it in a form, and in language adapted to the general and the juvenile reader. And, holding to the young persons to whom these Letters are more immediately addressed, the relation therein indicated, and writing under the promptings of that relation, he has not hesitated; as occasion offered, to introduce such ob-

PREFACE.

xiii servations as might lead them (and others of their tender years into whose hands this little book maycome) to associate Nature with God, and Natural Truth with Revealed; and^ in the words of the late venerable and revered author of the Essays on the Nature and Principles of Taste^ to look upon the universe which they inhabit, not as the abode only of human cares or human joys^ but as the temple of the Living God, in which praise is duC; and where service is to be performed."

Southampton^ December 5, 1855.

Contents

PAGE

LETTEE 1 1

Introduction. Questions as to tlie natural longevity and size of trees. Footing on whicli these questions rest : twofold — Istf that every tree is an individual or single plant ; and, 2ndly, that all living beings have a determinate duration of life, and a determinate size of organism. Grood grounds exist for believing that the latter assumption is well-founded. On the supposition that the former is also well-founded, nothing yet known as to the natural age or size of trees. Doubts as to the validity of the assumption. Question whether a tree is not in point of fact an aggregate of individuals — a body corporate, — consisting, at midsummer, of a collection of living yet perfectly distinct OMnual tree-plants, the produce of the year, and of the dead remains of a still larger number of individual plants of th e same species , the produce of preceding years ; the living plants evolved from huds and growing as parasites on the organic remains of the dead plants. If this be the real nature of trees, there will be no natural limit to their age or size. G-enealogical tree.

Letter II 11

Inquiry as to the extent of our knowledge regarding the natural age and size of trees, on the assumption that every tree is an individual plant. The popular belief; vague. Information contained in systematic treatises on botany — by Professor Balfour, M. Richard, M. De Candolle : its unxvi

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satisfactory character. Information contained in books which treat expressly of trees, e.g., Griipin's Forest Scenery : equally unsatisfactory. Difficulties attaching to the inquiry from the circumstance that we nowhere see trees presenting indications of natural old age, and that we see everywhere trees of great age — as old, in fact, and as large, as any of their kind have ever been known to reach — still growing as vigorously as in their earliest years. Remarkable statement in Isaiah Ixv. 22.

Letter III. 25

Corporation-theory of trees resumed. Re-statement of this theory. The theory itself only a part of a more general theory in Vegetable Physiology. Statement of this general theory. All plants, even those called perennial, really annuals — some wholly disappearing by decomposition at the end of the year they are evolved, — portions of others remaining for ulterior purposes in the vegetable economy of nature, but still remaining only as dead organic matter. AU plants evolved either from seeds or buds, or both. Buds equivalent to seeds, and merely fixed or adherent seeds. The produce of the buds of trees identical in character with seedling tree-plants ; and trees themselves merely the product of tree-plants issuing from buds and growing parasitically on the persistant dead remains of the tree-plants of former years. Inferences : Is^, trees, as such, without natural limit to their age or size ; 2ndly, tree-plants, however, live but one year, and attain to a comparatively small size.

Subject continued. The persistent dead remains of the tree-plants of former years serve to the living and growing plants of the current year the purposes of a permanent mechanical support and of a temporary soil. Illustration of these statements as regards the two great divisions of the tree tribe. And, 1st, as regards the Exogen. Disposition of the plants as successively developed year by year in the vertical direction. Plan of fir tree. The bud at the summit of the first year's plant sends upwards a new shoot and

CONTENTS.

XVll downwards new roots, these roots in their descent pass alongside the shoot and the roots of the plant of the previous year, and thence extend a short way beyond into fresh soil. And so on. Disposition of the bark. The terminal bud and its relation to the pith contained in the medullary cavity. Qualification of the statement that the plants issuing from the buds actually send down roots.

Letter V. 89

Examination of the parts composing the Exogen, as viewed horizontally or in the transverse direction. Cellular tissue. Relation of the woody tissue to the cellular. Medullary or pith cavity, medullary rays, medullary ring or cambium, and bundles of woody tissue. Disposition of the woody bundles often irregular — eccentric character thus given to the concentric woody rings. Gfrouping of the woody bundles into sets or parcels — columnar or buttressed character thus given to the trunk. Winding or erratic course of woody fibres or bundles. Identity of woody tissue above ground with that underground. Antagonism between the woody and the cellular tissue. Elm at North Stoneham, Hants, with roots filling up the decayed bole.

Letter VI. 49

Examination of the parts composing the Endogen. The palm — disposition of its parts. Bud of palm — sends upwards leaves and fiowers, and downwards roots— these roots pass inside the remains of the palm-plants of former years. The palm-plant has no proper stem, and the palm-tree no proper trunk. Roots of the palm-tree fibrous like those of grasses, and derived from the palm -plants of the first few years. Aerial roots of certain palms, piercing through the trunk, passing down through the air into the soil, and forming props for the support of the palm-trunk. Slender hold which the palm-tree has of the ground.

Letter VII . 54

Harmony of the Corporation-theory of trees with the known history of many trees still extant and remarkable for their

h

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age and size. References to very old and large 'trees — yewS;, courbarils, American cedar, boabab, gum-dragon tree, deciduous cypress, the banyan, enormous plank of timber, Wellingtonia gigantia.

Question— "Why, if this theory be sound, very old and very large trees are not more numerous than they really are] Explanation— All trees subject to accidental" death from extraneous causes, and are sooner or later, and some kinds of trees more speedily than other kinds, thereby destroyed. Enumeration of these causes.

Letter VIII 68

Evidence adduced in support of the theory. Two-fold — Is^, that the growths emanating from the buds constitute severally perfect and independent plants, and that a succession of such plants may be kept up from year to year for ever from buds alone ; and, 2ndlyy that at the end of the year, the plants thus evolved (save the buds only) die and never live again.

First branch of the evidence taken up and pursued. The produce of the buds includes all the parts entering into the constitution of the most perfect seedling plants, viz. : stems and roots, leaves, flowers, seeds and buds. The bud can evolve the seed. Illustrations furnished by the potato, the strawberry, and the processes of grafting, slipping, and layering. Mr Knight's view as to the dying out " of fruit-trees opposed to the theory : his view erroneous.

Letter IX 79

Second branch of the evidence taken up- and pursued, viz. : that at the end of the year the plants emanating from the buds die. The only parts of the plants that then remain are the stems and roots, the other parts having dropped off. Proofs that these stems and roots die at the end of the year. Gfeneral considerations as to the very transient duration of vitality in all organised structures : the continued vitality of any structure only possible by a continual change of substance, called by physiologists interstitial or molecidar nutrition. This process obtains in

CONTENTS.

xix animals : does not obtain in any kind of vegetables. Inferences.

Additional considerations regarding the absence of this process of molecular nutrition in plants, intended to shew the identity between the perennial tree and the mere annual in respect of their vitality, and the difference between plants and animals. These considerations drawn from the different objects for which plants and animals respectively have been created. Obj ects of animal existence. Obj ects of vegetable existence — illustrations — corn-producing plants, timberproducing plants — the objects for which each of these exists accomplished year by year. Inferences as to the vitality of the persistent annual stems and roots of trees. Moreover, after the year they are formed, these stems and roots undergo no change in the way of growth or extension.

The proofs hitherto adduced may be thought incomplete or insufficient. Although the stems and roots undergo no nutritive or other organic change after the year of their formation, the living sap moves or circulates through them. Hence a presumption that the parts in Question still continue to be possessed of vitality. That presumption, however, erroneous. Why : the stems and roots of the previous year no otherwise concerned in the movement of the sap than passively and as mere channels of transmission. The circulation of the sap a vital process, and due to vital agency ; but this agency seated in the living and growing - parts — buds, leaves, ca^mbium, and spongioles of the roots, and the cause both of the ascending and the descending currents. No good grounds exist for ascribing vitality or vital agency to the old stems and roots. Further, in the course of time, these stems and roots undergo decomposition without this affecting the vitality of the growths siibsequently evolved from the buds.

Letter XI 103

Arguments in support of the Corporation-theory of trees, derived from the concurring and independent views of various

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authors, e.g., M. Du Petit-Thouars, Mr Appleby, Dr Ware, M. Mirbel., M. Gaudichaud, Professor Owen.

Letter XII 122

Objections to the theory considered. - Greneral nature and grounds of these. Nature of the woody layers annually formed in Exogens — these layers serve various purposes — still they are both virtually and actually roots. Mode in which they are evolved peculiar. Admission that they are • primarily formed in situ and from the cambium, as maintained by Mirbel. Relation of the cambium to the bud — the cambium continuous with and an integral part of the bud — an extension of it in adaptation to the circumstances and objects of existence of exogenous tree-plants. Constitution and structure of the cambium — product of its development ; this not wholly evolved in situ— 2, certain portion growing and creeping downwards. This latter portion undeniably root and specially the rooi— the former, or that formed in • situ, a provision for bringing the root proper into relation with the shoot emanating from the bud. No natural or structural difference between the part above ground and the part under ground ; the tissue of the one continuous with the tissue of the other, and identical throughout with roots. Mode in which the cambium is developed into cellular and woody tissue.

Letter XIII 134

Evidence in favour of the assumption that the woody layers in Exogens are of the nature of roots. Whenever circumstances admit of it, the woody tissue of the trunk grows and comports itself as roots do ; processes of slipping and layering. North Stoneham elm, with roots filling up a chasm in the bole — other examples of this. Aspect of a piece of hardwood timber denuded of its bark. Relation of branches spreading southwards to roots spreading northwards. Disposition of the woody fibres in the thorn, the poplar, the beech, and the yew. Spontaneous division of trunk of thorn into lesser stems. Fibres descending from a branch in Draccena and spreading over the trunk ; graft

CONTENTS.

xxi of Rohinia hispida sending down roots on dead stem of Robinia pseudo-acacia. Actual descent of woody fibres in the palm — virtual descent of these fibres in the trunk even of Exogens ; Dr Lindley's opinion as to this point.

Letter XIV 145

Evidence continued. Unequal growth of the woody layers in the same tree in different years and on different sides of the trunk — these differences directly related to differences in the number of the plants emanating from the buds, to the vigour of the plants, and their position on the tree. The development of the cambium into wood dependent on the buds and their produce, i.e., on the leaves, and that in a way not referable merely to supplies of elaborated sap furnished by the leaves. The wood not wholly developed in situ. An actual as well as a virtual descent, in some way, of woody tissue from the leaves. Holly-and-chain piece.

Letter XV 155

Dr Carpenter's objections to the theory. Partly general, partly special. In as far as general, various — these considered. Argument founded on an elm, referred to by him, considered. Argument founded on the structure and constitution of the cactus considered.

Letter XVI 167

Dr Carpenter's special objections to the theory considered. These twofold — 1st, that the buds and cambium -layer, and their respective produce, are merely continuous products, and an extension of the existing tree. 2ndly, that the buds of trees are not co-ordinate with the seeds, and that only the produce of a seed can be regarded as an individual being. The former objection taken up and discussed.

Letter XVII 177

Dr Carpenter's second special objection taken up and considered. The seed itself, in a like sense as the bud, merely an extension or a continuous product of the parent plant. The bud can evolve all that the seed can. No real difference between two trees, e.g., two willow trees, raised, the one from a seed, the other from a bud. Exceptions taken to

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I

this assumption, and allegation made that the bud reproduces only its own variety of the species, while the seed reproduces the species itself. Alleged dying -out of the produce of grafts. Other exceptions taken. Difficulties attaching to Dr Carpenter's view. Gremmiparous and oviparous reproduction identical in nature. A single cell the primary element in the reproductive process, and the bud the primary seat of this cell.

LETTEE XVIII :

Mutual relations of the bud and the seed. The two identical in their nature ; but the bud the primary mode of the reproductive process, and the seed a modification of the bud in adaptation to special ends : these ends, though they have a place in vegetables and animals generally, point to man and to man's moral and social nature and the institution of marriage as their primary source and origin. This view pursued at some length. Man's twofold nature and relations : an organised being and as such allied to plants and the lower animals and to the inorganic world ; a spiritual being, and as such allied to Gfod and the world that is to come. Uniformity or unity of plan observed throughout the whole of nature. Quotation from Professor Powell as to this. Application of the views advanced to the hypothesis suggested. The bud might alone have sufficed for reproduction, both in vegetables and animals, and even in Man. Adam, formed first : Eve afterwards ; Eve the off- . spring of Adam and evolved from a rib as from a bud. Reasons given in Scripture for Eve^s creation. Woman's mission. Inference.

The bud at least co-ordinate with the seed : both answer the same end, but each in a way that the other cannot. How sometimes the one, sometimes the other, and sometimes both together, are made use of by Nature. Importance of the bud in the economy of Nature — seen in timber and coal.

Practical applications of the Theory. Its uses in the ex-

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xxiii planation of phenomena and in the solution of questions connected with trees — its uses to the gardener and the forester. Apology and protest. Suggestions. — I. Cautions as to pruning and precautions as to planting and thinning. II. The fact of the tree-plants of each year being essentially independent of those of past and subsequent years, aground of hope to the landowner that a disease affecting his plantations for one or even for a series of years,, may be but temporary and not permanently injurious. Disease in its own nature essentially temporary. Eecovery of diseased larch plantations. Probable final recovery of the potato, the h.op, the vine, and other plants from their " disease." Possibly some qualification of this expectation requisite in the case of trees — the timber produced by diseased plants perhaps unsound, and may affect the adjacent sound timber. '^Dry rot " in timber.

LETTER XX 213

Application of the theory to questions in natural theology. Laws of Nature : what they are ; various definitions given of them — Dr Alison's, Dr Thomas Reid's, Plato's, (Ersted's. ' Illustrations. What the law written upon trees ; what the language which they speak. Conclusion.

POSTSCRIPT 223

Annual and prospective money-value of larch and Scotch fir plantations.

APPENDIX 229

LETTERS ON TREES.

Letter 1

As the days of a Tree, are tlie days of my People," Les Jours de mon Peuple egaleront les Jours des Arbres/'

Isaiah Ixt. 22.

1. The Winter is gone, and Spring is come again. The Sun, ''hke a giant refreshed with sleep," is again putting forth his strength ; and under his influence, as the instrument of Him who made and still upholdeth all things, " the earth is again rising as from her grave into life and beauty." What season more fitting to take up our favourite subject — the Trees, and to pursue those speculations regarding their natural longevity and size, and likewise regarding their real nature, which have so often, in the fields and by the fireside, formed the subject of our casual conversation. The buds on manj^ sorts of trees are already swelling, and the sap in the immediate vicinitj^ of the buds is

A already in motion, — to be followed, ere long and in quick succession, by the evolution of leaf, and flower, and fruit, and wood, and root, and by a perfect circalation of nutrient fluid in all the living and grow'ng parts; and all this to be succeeded before the Tear has run its course, by the faUing of the leaf, the c^ropping of the fruit, and the cessation of all vital action in what remains.

2. Taking up the subject now, ere yet the annual process of vegetation is well begun, and following this process through its several stages, we may have it in our power in the course of the season to make for ourselves observations enough, and experiments enough,

, to satisfy us whether our speculations be true to nature and to fact.

3. Of Trees in general, then, as of particular kinds of trees — for example, the Oak, the Elm, the Beech, the Fir, &c. — it may be asked, and often is asked, " How long do they naturally live ? " And, To what size do they naturally grow ? "

4. Before proceeding to consider the answers to be given to these two questions, let us clearly understand on what footing the questions rest. To most, if not to all who entertain them, the questions proceed on the assumption that a tree is a single object, in a sense precisely analogous to that in which an ox or a horse is so regarded; they imply that every tree is as truly an individual being, corporeally regarded, as each of

LETTER I.

us is ; and has as real a personality as belongs to our mare Fanny or our dog Ccesar.

5. Nor is this all. They proceed also on the principle, that however the appointed term of life and size of organism may vary in the different sorts and species, all living beings without exception are subject to the law both of a determinate duration of life, and of a determinate size of organism.

6. And this principle is unquestionably a sound one. No law of nature is more absolute or universal than the law of mortaUty. Everything that hves, be it plant or animal, lives only for a given time, on the expiry of which it passes into the state or condition of death. Nor is this left to be brought about by accidental causes. To these, indeed, it is often owing, the greater number — probably of all sorts — of living beings thus prematurely perishing. But independently of such causes, the loss of its vital properties, and the cessation of its vital actions, is a fundamental law of the constitution of every living being. The conditions of its existence include within themselves provisions for its dissolution. The arrangements to which it owed its origin, and by which its vital actions have been since performed, are such as unfailingly ensure after a time the extinction of its vital powers, —

Such changes are gradually wrought in it by the

LETTERS ON TREES.

agency of its own vitality, as are ultimately incompatible with the longer continuance of life. Death then follows as a matter of course. And those changes are attended by a gradually increasing languor or sluggishness in the vital processes, and by a corresponding hardening and rigidity of the textures composing the organism, — changes that constitute and betoken the state to which the name of old age is given ; a state which obtains uniformly when life is not prematurely cut short, and is indicative of the approach of death.

7. Again, all organised bodies have an appointed size or bulk of organism. Of lifeless inorganic bodies, it cannot be affirmed that they possess any such property, being larger or smaller, to any conceivable extent, according as circumstances may determine. It is otherwise, however, with animal and vegetable organisms. These have naturally a fixed or standard size to which they grow, and from which they never greatly deviate.

8. I have perhaps needlessly gone into these details respecting this principle. But I have purposely done so, and for this reason, that, while the principle is confessedly one of the grounds on which the questions before us proceed, and one which I hold to be unassailable, no answer that may be given to the questions, that is not in conformity with it, can be regarded as satisfactory.

LETTER I.

9. If, then, every tree be a single or an individual object, it is plain that, by the laws of its being, it must have a determinate period of life, and a determinate size of organism ; and allowing that neither of these is absolutely fixed any more than in the case of the dog or the horse, but that each may vary within certain limits, there must nevertheless be an average in respect of both for each kind or species of tree — it being of course understood, that all the conditions requisite for its natural life and growth, obtain. And accordingly, the questions before us thus qualified are — " How long does this or that kind of tree naturally hve V And, " What is the size to which it naturally attains ?"

10. These questions, you may imagine, must admit of a ready and a satisfactory answer. True, you may feel yourselves unable to answer them, and yet reasonably presume that our knowledge of all sorts of trees must be complete and accurate enough to make the answers easy to those possessed of that knowledge. They are not far to seek, speaking generally, as regards animals. Migratory as animals are, difficult of access or dangerous of approach as many of them are, these points in their history are accurately known, or may readily be ascertained in regard to a large proportion of them. How much more easily in regard to trees ! Fixed to the soil as trees are, remaining always on the same spot of ground in which they were first planted,