ARBORICULTURE.-XI

Globe, Volume XXIV, Issue 2642, 26 September 1882, Page 3

ARBORICULTURE.-XI

In concluding thoie papers upon the above subject:, I would draw toe attention of all planters to the fact that a knowledge of the structure and physiology of trees is the only true guide by which trees and soils can be brought into harmony, and having an insight to the various actions exhibited daring their growth, enables men to account for and grapple with the numerous hindrances to forest tree planting and roaring. Besides this material benefit from the study of trees, we have a greater interest, and as our tastes and intellect increases our lives become ennobled, happier, and brighter, because in thing* around ns we. see numerous spring* of pleasure. As an incentive to (boss occupied in the planting of trees, I will endeavor to give a plain idea of a tree and its workings, leaving out s* much as possible all scientific terms. Development towards a high state of perfection hoe undoubtedly been the ruling motive or ultimate object of those immutable laws which have governed and are now ruling the works'of nature. This is not only clearly seen in the studying of the animal kingdom as laid bare by geology, but in the vegetable kingdom we have as great a proof of development ; and as man is looked upon as the olimex of the animal series, so an exogenous tree is the highest state of perfection as yet arrived at in the vegetable world. A tree, to those who have never tasted the sweeta of science, is nothing—the bursting of the bud, imperceptible growth, fall of the leaf, and period of rest, are to them simple facts, and the why and wherefore of such thing* never cross thoir mind. But students of nature have a multitude of pleasures and sources of enjoyment which arc unknown to others, and men who pass- through life without a knowledge of creation and the wonderful laws regulating all effects, know not what a beautiful world they have been living in, what countless wonders tbey have never seen, and in point of fact hardly know that they have been in existence. Trees have played an important part in the history of thie world, and when we take into account coal, ships, houses, implements, &0., there is nothing which has conduced so much to the happiness and progress of the human race as trees, and yet of all natural objects they have been the least studied popularly. Looking at a fully developed tree on a calm day, all seems still as death (and but for the wind it is always so to the naked eye)—not a motion can be observed, and to all appearance it is lifeless. Yet within and without all is activity, the whole tree is a veritable laboratory, n natural workshop, where all is life. Even whilst wo are looking at the tree marvellous phenomena are continually taking place, and chemical actions and effects on a more wonderful scale than ever takes place in the laboratory of a chemist. The tree to all intents and purposes is a moving mass of life, ever doing and ever changing, constantly performing the functions allotted to it by the Great Designer of Nature in the economy of the universe. To have an idea of these remarkable phenomena taking place around ns we must commence at the very base, and as it were follow up the life history of a tree. Taking an acorn we perceive a hard, crisp, white substance, easily divided into two equal portions, contained in a tough leathery case-; at the base of these two halves we find a small prominence of the same substance, and connected with them. This is the embryo, or strictly speaking the future oak tree on a diminutive scale. In it we can discern the root and stem, and when tbo acorn is placed in the ground and becomes subject to the influence of heat and moisture the miniature root descends, the item aicencs, both deriving material for their growth from the white halves of the acorn. By the time the nutriment of these halves is entirely consumed the young root has prepared itself with means of obtaining food from the soil and the stem prepared itself for the purifying of this food, which is of a necessity taken np in a crude state. The life of a young tree consists of obtaining food, purifying, and utilising it, and in performing theca functions we hove presented to our notice provisions and contrivances on an equality with those so often witnessed in animal life. Examining the root of this young oak tree we soa that it branches in all directions, and that the numerous fibres make their way through the compact soil with such ease, freedom, and accuracy, that we are bound, to a certain extent, to look upon these fibres as being endowed with an amount of sense. On a closer inspection we find that every branohlet of these numerous root fibres is furnished as the apex with a differentiated mass of tissue, or what is technically termed a spongiole. It is tee apox which hunts after tho necessary food and absorbs it into the plant, and when we watch the movements through the soil, as it presses on toward® the richer parts around the tree, wo are at once struck with a wonderful contrivance by which it surmounts all difficulties, works round stones, rocks, and pierces hard soils. If roo:a increased in length from the base, and so pushed out, as leaves do, tho result would ba, when it came in contact with a hard substance, a turning back upon itself, aud so impoverish the tree j but nature haj made the tips of roots growing point,;, and instead of having to push their way through the soil, they add cell by cell to tbo root tips, and, au it were, build themselves through the soil, adapting the size and of tho fibres to the material in which they are working. Many interesting instaucßS might be quoted, showing tbo eccentricities of roots and what they are capable of doing, but the most remarkable freak ever seen by mt was in the mountainous regions ot S.E. Africa (dekukuna’a country) a land consisting of oaves and waterfalls. In one of these endless oaves, far into the bowels of a mountain, I noticed the branching roots of a tree spreading about the floor, and dis appearing down crevices and fissures, f racing these roots to a main stem, adhori-jg firmly to the side c£ the cave, I could have imagined that a true was growing there, but for the disappearance of this trunklike root through an almost imperceptible crack in the roof of the care. These giant root® were alive, and wore passing up through the mountain nutriment for tho supply oi a giant tree which at least must have been five hundred feet higher than the floor of the cave. In seeing how roots spread in switch of material for building up the tree, ■*.- observe the method by which this material 10 got into the tissues. Speaking plainly, it i i a kind of suction or what scientists call endosmose, for in those root tip* we find no holes, pores, or any opening by which the fluid flood 1 of plants can pus into the roots, and yet we

osn (ee it being absorbed. This peculiar phenomenon it easily explained by the fast thr.c a fluid substance will past through nonporoui ticiue into a viscid substance, or in other word*, water will past through abU drr into treacle. Therefore, at the contents of tae cells forming the spongiolei are thicker than the water holding the necessary ingredients in eolation, the latter pastes through the ceil walls, and so into the tissues of the roots.

BetumiEg to our ideal oak tree, wa etc the young roots branching and re-branching in all directions, with every fibril armed with a spongiole, and busy imbibing the dissolved constituents of plants. The fluid, or what we will call crude eap, passes along the roots into the miniature stem, ascends to'the leaves, and there undergoes a preparation necessary before it csn'ba utilised in forming vegetable substance. In the young tree the crude *ap is deprived o! all unnecessary ingredients, and is elaborated as it ascends the stem ; for, in the first stage of growth, the green stems can perform the rant functions as leaves. In this wise provision wo see that the whole plant is engaged in the manufacture of a substance commonly called •ap, out of which all the cells and veraalt used in forming the tree are made. This haste, or activity, soon results in the formation of vessels strengthened with deposits of lignins, and hence a stem capable of withstanding the winds. In the course of a few yoirs the stem of our oak tree becomes thicker, harder, and loses the pith which once formed, with the green bark, the whole of the stem, through which the crude sap permeated and passed into tissue. Now all this has disappeared, and wo have a tongh brown bark incapable of elaborating the sap, and a hard centre complexly choked up by deposits cl lignine and pressure from the continually forming vessels outwardly. It is now, when the tree has arrived to the full vigor of its life, that wo can look into and judge of the manifold wonders continually taking place in and around it. In the first pkee wo have a fluid substance being drawn into the roots, on to the stem, and then upwards into the branches and out to the leaves. Here is action entirely opposed to the general idea of gravity; for how is it that this sap ascends. To say that it doss so under the influence of capillarity, similar to suspending a piece of worsted thread and allowing the end to came in contact with water which pessos up to where it is tied, or dhplacement, as witnessed in a siphon, is entirely misleading, for in the first place it would render a descending sap an impossibility, and would not account for the effects ligatures have upca trees. Many ideas have been put forth as elucidations of this mystery, hut hitherto they bars failed in accounting for the results of various experiments. Having for a good many years been engaged in the studying of trees and (heir functions, my mind has ever and wen been centred upon this point; and although I have never seen it mentioned by any scientist, the following is the result of my observations ; end will, so for us I am able to judge, account far the circulation of rap is trees.

A cork placed at the bottom of a bucket o£ water will come to the top, b.eauis the water is heavier than the cork; oil will do the same ; yet there are many fluids whiqh would sink to the bottom. On the same principle tho crude sap absorbed by the roots is lighter than the contents of the cells and vessels through which it passes on its upward course. Figuratively speaking, the bark and cambiumlayer are analagous to the bucket and the alburnum or sapwood to the water. Eadosmose or the passing of one fluid into another, is certainly a form of gravity, and when we see crude sap passing through cell walls tq cells, aud so on until the leaves are reached, where, after getting rid of a quantity of go®, &c, it seems to increase in weight, and then commences to descend through the innermost layer of bark and the contiguous vessels, we must conclude that this is gravity also. The assertion that the ascent of sap in tress ie opposed to the laws of gravity is o« erroneous as if applied to the ascent of oil through water. Every gardener knows that by binding a branch of a fruit tree to the ground it will cam a the production of more fruit, because the purified and bonce heavier sap cannot ascend up the bend which is formed, and must therefore be all devoted to the fruiting spars. On the other band, the small side branches which have been thrown into an erect position by the bending of the- rent branch, will have the bu k or the it j crude sap thrown into them, and inoreato in sizs at the expense of the parent branch, which has its full supply out off by being bent. This instance alone proves, to my mind, that the difference in tha specific gravity causes the esoent and descent of sap (crude and elaborated). Again returning to our ideal tree, we see, in imagination, the crude sap passing into the leave®, and there undergoing a variety of chemical actions. Before we can at all understand this most wonderful part of a tree’s life, we must have a true conception of a leaf. A leaf, strictly speaking, is a continuation of the stem tissue, covered with an expamion of the bark. The veins can be traced into the midrib, tha midrib into the wood of the bronohlets, branehlets to branches, branches to stem, and so on to the roots, until arriving at the spongioles. The green cellular expansion, connecting the veins, Ac., can b: traced to the bark or covering of tho leaf stalk, and then to the bark of branch os and stem. Looking at the sap, ws cee it creeping along the midrib into the veins, then into the minute veinlets, until it comes in contact with tho numerous intercellular passages which have direct communication with the atmosphere by opening on tha under surface of the leaves, called stomata. Into these intercellular passages all unnecessary ingredients brought np from the soil are emitted, and •so passed away from the tree in the shape of gas or moisture. At the same time gaseous eltmcnte required for tho transforming of the crude sap into matter suitable for the formation or woody layers are imbibed, and a general elaboration takes place. Daring this very interesting chemical process, the s«p passes from the vascular tisane of the leaves into that part which is connected with the bark, aud than starts on its downward tendency. Miking a transferee section of the slim of an enk tree, wo notice a number of rings commencing from the first one surrounding tho pith. These are caused by the annual activity of the tree, or, in other word*, the cessation of work in the tree during winter. On the outside of these annual layers of woody vessels wo have the bark, which consists of threo layers of tissue. Down the inner layer, and between that and the already formed wood tissue, we trace tbs pure sap from the leaves. Hero again wa have a number of marvellous phenomena taking place, and as we discern the rich mucilage gradually pass into a layer of wood we are tempted to take a cloier examination and see how it is accomplished. The already formed vessels immediately in con’act with the sap assimilate it, and having the power of multiplying, produce other cells whicb, owing to vertical pressure, assume spied Ic-sbopad bodies, aad arc then termed vessels. That is, we have a formative matter between the bark and the wood, which tab ss lor sap and forms woody vessels out of it. In this way the tree increases in size year after year, and a 3 each layer of wood is formed, the pressure upon the interior increases, which, with the deposits of iignino in tbo old vessels, results in a hard and solid timber.

Many points of interest could be considers;! in connection with the life of a tree; but tbs production of wood, or the budding up of a giant stem being in a forester's interest the main object of a tree, there ifi no necessity to go into them now. Summarising the varietur phenomena touched upon during the study o£ our ideal tree, we can, whilst looking at it in the full vigor of life, grasp to a certain extent the regular, noiseless, active processes going on within it. The re"*- busy eearohing for food, the tissue of the stems carrying it up to the leaves, las leaves manufacturing the pure sap, and the cambium layer forming the circles o: wood, unite us one harmonious notion. Destroy the leaves, and the of tho roots would be wasted; injure the roots, and the leaves droop and die ; take away the cambium by cutting the bark, and the root* and leaves parish. If the roots are healthy the who's tree is bound to fl:urisb, and in selecting tresa for different toils and localities the naturo and structure of tbs roots should bo the chief guide, apart from the analysing of tha young tree itself. Having ia.-j that tho .reo builds itself up from what is absorbed by tha roota from the soil, we can cosily dad cut tha best formation for any given tree to grow on, by reducing it to aober and ascertaining tho chemical composition the ash, which is the inorganic matter taker, up by the roots to aid in the formation of the wood. Tho lard containing in abundance the Bpocbl ingredients of the ash, providing it agrees with the nature of tha roots, is, of course, the moat suitable, and will produce the best trees. cma, Hvm