Harry Marshall Ward

“ It is not to these latter alone that our few existing ancient oaks are so attractive, however, and a slight acquaintance with the oaken roofs and carvings of some of our historical edifices affords ample proof that the indefinable charm exercised on us by what has proved so lasting, is a real one and deep-seated in the Saxon nature. In fact, everything about the oak is suggestive of durability and sturdy hardiness, and, like so many objects of human worship in the earlier days of man's emergence from a savage state, the oak instinctively attracts us. ”

“ He not only laid bare the complex facts of the life-history of many forms,—e.g. the Ustilagineae, Peronosporeae, Uredineae and many Ascomycetes,—treating them from the developmental point of view, in opposition to the then prevailing anatomical method, but he insisted on the necessity of tracing the evolution of each organism from spore to spore, and by his methods of culture and accurate observation brought to light numerous facts previously undreamt of. ”

“ The timber itself is remarkable for combining so many valuable properties. It is not that oak timber is the heaviest, the toughest, the most beautiful, etc., of known woods, but it is because it combines a good proportion of weight, toughness, durability, and other qualities that it is so valuable for so many purposes. The richness of the cortex in tannin warranted the growing of young oaks at one time for the bark alone, and the value of the acorns for feeding swine has been immense in some districts. ”

“ It will be understood that this plumule also is living at the expense of the food stores in the cotyledons, the dissolved substances passing up into it through the tiny vascular bundles and cells, as they have all along been passing down to the growing root through the similar channels in its tissues.
The plumule—or, as we must now call it, primary shoot—differs from the root not only in its more tardy growth at first, but also in its habit of growing away from the center of gravitation of the earth and into the light and air ”

“ It is of the highest importance to understand that a bud is simply the young state of a shoot, and that it consists of the growing-point of the shoot enveloped by closely-folded leaf structures. In the oak the buds are already formed before the end of June, and on looking closely into the axils of the leaves on the young shoots—which have by that time ceased to elongate to any considerable extent farther—they may be seen as small, green, hairy bodies. ”

“ When a cambium cell passes over into wood-parenchyma it first undergoes a few horizontal divisions transverse to its long axis, and then we have a vertical row of five or six parenchymatous cells, the walls of which do not thicken much, but obtain small simple pits, and retain part of their living contents—protoplasm, nucleus, starch-forming corpuscles, etc.—and indeed present much resemblance to the cells of the medullary rays themselves. ”

“ The extreme tip of the root proper fits closely into the cap, and evidently adds cells to the inside of the latter, and thus replaces the old ones which are worn away. At this true tip of the root, moreover, we make another discovery, namely, that all the cells are there alike in shape, size, and other peculiarities; and if we could take a transverse section exactly at this place we should see no differentiation into axial cylinder and root-cortex, etc.; the small circular mass would consist of cells all alike, and with very thin walls and full of dense protoplasm. ”

“ This peculiarity of turning downward is so marked that it manifests itself no matter in what position the acorn lies, and it is obviously of advantage to the plant that the radicle should thus emerge first, and turn away from the light, and grow as quickly as possible towards the center of the earth, because it thus establishes a first hold on the soil, in readiness to absorb water and dissolve mineral substances by the time the leaves open and require them. ”

“ We are now in a position to understand generally the changes that convert the female flower into the cupped acorn. The fertilized oöspore becomes the embryo (Fig. 35, x) ; it grows at the expense of the contents of the embryo-sac, and develops a radicle, a plumule, and two relatively large cotyledons, which soon become so big that they occupy the whole space in the sac (Fig. 36) . Moreover, the embryo-sac increases to make more room for this growing embryo. And now comes in a curious point. We saw that the ovary consisted of three chambers, each containing two ovules ”

“ By this time, however, the symmetry of the root-system is being disturbed because some of the rootlets meet with stones or other obstacles, others get dried up or frozen, or gnawed off or otherwise injured, and the varying directions in which new growths start and in which the resistances are least, influence the very various shapes of the tangled mass of roots now permeating the soil in all directions. ”

“ The first indication of the development of the cork is the conversion of the sub-epidermal layer of cortex-cells into a meristem—i. e., the cells become capable of active growth and division.
Each cell of the layer referred to may be termed an initial cell of the cork-cambium (or phellogen) , and the layer may be called the initial layer. This layer behaves essentially like the cambium of a fibro-vascular bundle, except that its daughter-cells become cork and phelloderm instead of phlöem and xylem. ”

“ As we have seen, the forester has to exercise considerable forethought—the outcome of long experience—in growing oak so as to obtain long, clean stems. The natural habit of the tree is to form a short, thick bole and a widely spreading crown, the main branches of which come off not far from the ground. To compel the stem to elongate into a long pole he has to plant other trees with it (as we have seen, beech, spruce, etc.) ”

“ The vascular bundles are practically pipes or conduits which will convey these materials from the cotyledons to the radicle and plumule as soon as germination begins, and I shall say no more of them here, beyond noting that each strand consists chiefly of a few very minute vessels and sieve-tubes. The young epidermis takes no part either in storing or in conducting the food substances; it is simply a covering tissue, and will go on extending as the seedling develops a larger and larger surface. ”

“ In later years the length of the cambial cells increases, and hence the length of the elements in the wood.
The phloëm or bast of the individual bundle is separated from its neighbors by large rays of parenchyma, the cells of which agree with the secondary bast-parenchyma rays. As these pass into the cortex they widen, as they do at the pith (Fig. 12) .
The oldest portion of the phloëm—that next the cortex—consists of a group of thick-walled bast fibers with their lumina nearly obliterated; these are long, spindle-shaped fibers much like the fibers of the wood. ”

“ When the radicle commences to bore down into the soil it puts forth a large number of root-hairs from the parts a few millimetres behind the tip, and these attach themselves to the particles of soil and supply points of resistance; the tip of the radicle is protected by the slippery root-cap, and it must be borne in mind that the embryonic tissue of the growing-point consists of thin-walled cells full of relatively stiff protoplasm with very little water. Hence the growing-point is a firm body. ”

“ The exact mechanism of the movement in the stem itself is too complex for discussion here; but I may sum up the matter by saying that the disappearance of the water at the surfaces of the leaves starts a series of flows in directions of least resistance towards the mesophyll, and as long as the evaporation goes on more water flows into the cells, to replace that lost, from the vessels of the stem, when the water-columns are supported and moved partly by capillarity and by the air-bubbles in the cavities, and partly by a peculiar co-operation of the living cells of the medullary rays. ”

“ The exterior of the very young stem or branch is smooth or slightly pubescent, the green color gradually passing into a silver-gray as the periderm develops, and in a few years (when the shoot is from five to twenty years old, or thereabout) the gradually thickening bark is shining and turning browner, flecked with lenticels and lichens. ”

“ As so often happens in the study of science, we have in the oak a subject for investigation which presents features of intense interest at every turn; and however much the new mode of looking at the tree may at first sight appear to be opposed to the older one, it will be found that the story of the oak as an object of biological study is at least not less fascinating than its folk-lore. ”

“ In each successive season of growth the young oak develops more leaves than it did before—in other words, the total area of the leaf-surface exposed to the air and sunlight is larger each successive summer than it was the previous one. ”

“ When ripe the wind blows the pollen as it scatters from the dangling stamens, and some of the grains reach the stigmas of the female flowers; here they germinate, each pollen grain sending a delicate pollen-tube down the style into the ovary of the flower. This process of application of the pollen grains to the stigma is termed pollination, and depends on the wind.
The female inflorescences are also spikes (Fig. 32, A) , but they bear only one to five flowers, and stand off from the axils of the foliage leaves. ”

“ The next point to bear in mind is that these medullary rays (like the pith and cortex) are merely parts of the general cell-tissue, or fundamental tissue, through which the vascular bundles run upwards and downwards with a tangentially sinuous course from the leaves. The primary medullary rays, therefore, are merely spokes, as it were, joining the pith and cortex ”

“ While the pollen-tube is descending the style, the ovules have arisen as minute cellular outgrowths from the angles of the three chambers of the ovary (Fig. 34, d) . There are two in each chamber. Each ovule is at first a mere solid lump of cells (nucellus) , which curves and becomes enveloped in two thin investing layers, called integuments, as shown in the figures A-D (in Fig. 35) . Inside the solid nucellus, n, of the ovule there soon arises a small cavity filled with nucleated protoplasm, and termed the embryo-sac, e, because the embryo is to be developed in it. ”

“ The chief diseases of the roots now arise from their spreading into unsuitable soil, the drainage of which may be incomplete, and thus bring about a sodden, acid, ill-aerated condition. The want of oxygen and the low temperature combine to kill the root-hairs and young rootlets, and the leaves above part with their water faster than it can be supplied from below, and they turn yellow and die off, the branches dry up, and the tree dies. ”

“ It is also a common practice to cut back oaks, and allow them to sprout into what is known as coppice—that is to say, numerous buds which would not have developed at all are impelled to grow up into twigs and branches (stool-shoots) from the lower parts of the cut tree. It was very usual at one time to grow oak in this way for the sake of the bark, which was employed in tanning, the trees being cut back again and again, and renewing the coppice growth after each cutting. ”

“ Summing up these essential features of the structure of the ripe acorn and its contents, we find that the fruit contains within its pericarp (which is a more or less complex series of layers, of which the outermost is hard) the seed; that this seed comprises a membranous testa inclosing an embryo; and that the embryo is composed of two huge cotyledons, a minute radicle, and a still more minute plumule; and that the tip of the radicle is turned towards the pointed end of the acorn, lying just inside the membranes. ”

“ Hardness.—Oak is neither the hardest and heaviest nor the most supple and toughest of woods, but it combines in a useful manner the average of these qualities. Good oak is hard, firm, and compact, and with a glossy surface, and varies much; young oak is often tougher, more cross-grained, and harder to work than older wood. According to Gayer, if we call the resistance which the beech offers to the saw, applied transverse to the fibers, 1, then that of freshly felled oak = 1·09. ”

“ If we shortly summarize the above we find that the root consists of an axis-cylinder surrounded by a cortex and the piliferous layer. At the tip the whole is covered by the root-cap, which is organically connected with the embryonic tissue which forms all these structures. The axis-cylinder is somewhat complex; it is sheathed by the endodermis and the pericyle, the latter of which gives origin to the new rootlets. Inside the pericycle are the vascular bundles running up and down as separate, alternate cords of xylem and phloëm ”

“ Some of these are referable to the exigencies of the non-living environments—the climate, soil, etc.; others are due to the attacks of living organisms, both vegetable and animal—from the weeds which smother the young seedlings by keeping the light from them, to man himself, who injures the trees in various ways. The earliest struggles of the young seedling are with the weeds, slugs, and insects of various kinds that invade the territory on which the acorn has germinated ”

“ Although the root-system of the young plant is regularly constituted of a series of lateral rootlets springing from the primary root, the orderly arrangement is soon disturbed when the tertiary and other rootlets begin to develop from the secondary rootlets; moreover, as the age of the tree increases, the tendency to irregularity is increased owing to the production of rootlets of the higher orders at different places, thus interfering with the acropetal succession of the younger rootlets. ”

“ From the outer layer of cells—the piliferous layer, corresponding to an epidermis—root-hairs are developed at some little distance behind the root-cap, and these superficial cellular outgrowths also rise in acropetal succession, the older ones behind dying oS as the younger ones arise farther forward. If we bear in mind all that has been shortly stated above, it will be very easy to figure the behavior of the root-system as it penetrates the ground, and the following short description of the biology of the root may render the matter clear. ”

“ In the section (Fig. 9) , for instance, all the little bundles at the angles and outside the ring are cut at levels where they have abandoned the larger bundles and are bending outward through the cortex to the leaves; lower down we should find them joining to the larger bundles at various levels, and running down with them, just as strands from leaves at higher levels are now conjoined to make up these larger bundles. The group of vascular bundles which passes into the stem from the insertion of a leaf is spoken of collectively as the "leaf-trace." ”

“ The first changes which take place when the young, thin roots begin to thicken are—first the piliferous layer dies away and the outer cells of the cortex turn brown; then a cylindrical layer of cork is developed in the pericycle, and as this cork is impervious to water it cuts off the cortex from communication with the axis-cylinder, and consequently the cortex gradually shrivels up and is thrown off. ”

“ The cells of the medullary rays are seen in one, two, or several rows, each cell having the form of a parallelopiped or ordinary brick—the bricks being supposed standing on their narrow sides and with the long axes directed radially. The walls in contact with the vascular bundles are thickened, and soon become woody and beset with simple pits; the cells contain protoplasm and nuclei, and in winter become filled to crowding with starch grains. ”

“ Other destructive agents during these early phases of the life of the oak are cattle and deer, which not only tread down the shoots but also nibble them off, and mice, squirrels, etc., do their share of injury, as also do wood-pigeons and other birds. In the north of Europe the young plants suffer terribly from the ravages of a fungus named Rosellinia, the mycelium of which sends its branches into the roots and kills them, consequently entailing the death of the plant. The larvae of various insects also damage the roots and bring about injuries which may prove fatal. ”

“ Thus, in the oak, the phellogen gives rise to permanent tissue on both side, of the initial layer: those cells which lie on the inside become phelloderm (cortical cells) , those on the outside become transformed into phellem (cork) . The three tissues, phelloderm, phellogen, and phellem, are called the periderm.
It is obvious that the cork-cambium, by thus adding to the cortical parenchyma, is gradually driven radially outwards from the center of the stem. ”