Growth ring

“ In each of these cases the growth made is inharmonious and one-sided: the balance between the two intersecting planes of growth, or between the two opposite sides, has been lost. But when a tree is planted in the open, and when all the other conditions of growth are favourable, it grows harmoniously in all directions,—upward, outward, and all around. In other words, it is growing as a whole, growing, as it ought to grow, through every fibre [254] of its being, and yet maintaining a perfect symmetry of form and the harmony of true proportion among its various parts. ”

“ Thus, in all organised beings, there is a process of growth, mere increase in bulk as it were, and a process of evolution or metamorphosis, [Pg xxviii] in accordance with which certain parts assume a different form from the rest, in order the better to fit them for the performance of different offices. Should growth and development be uniform and regular, that is in accordance with what is habitual in any particular species, there is no monstrosity, but if either growth or development be in any way irregular, malformation results. ”

“ It is clear, I think, that we may account for many ordinary biological processes of development or transformation of form by the existence of trammels or lines of constraint, which limit and determine the action of the expansive forces of growth that would otherwise be uniform and symmetrical. ”

“ Each group supplies an approximate curve of its decreasing growth with age. So, after plotting the means, a long average line as nearly straight as possible is drawn through them. This gives the factor by which individual rings may be reduced to the standard adult growth ”

“ Adaptation comprises all structural changes resulting from adjustment. It includes both growth and modification. The latter is merely growth in response to unusual stimuli, but this fact is the real clue to all evolution. Growth is periodic, and in a sense quantitative; it results from the normal continuous adjustment of the plant to the stimuli of its proper habitat. In contrast, modification is relatively permanent and qualitative; it is the response to stimuli unusual in kind or intensity. A definite knowledge of the processes of growth is indispensable to an understanding of modification. ”

“ But the increase of size which constitutes growth is the result of a process of molecular intussusception, and therefore differs altogether from the process of growth by accretion, which may be observed in crystals and is effected purely by the external addition of new matter—so that, in the well-known aphorism of Linnaeus, the word “grow” as applied to stones signifies a totally different process from what is called “growth” in plants and animals. ”

“ The term growth ought strictly to be confined to mere increase of size, and development to change of structure. [916] Now, a child is said to grow into a man, and a foal into a horse, but, as in these cases there is much change of structure, the process properly belongs to the order of development. ”

“ Pierre, who says: “When the branches of a plant are disposed in a uniform plan of diminishing size, as in the pyramidal shape of a pine, there is progression; and if these trees be planted in long avenues, diminishing in height and colour, as each tree does in itself, our pleasure is redoubled, because progression here becomes infinite. It is owing to this feeling of infinity that we take pleasure in looking at anything that presents progression, such as nurseries in different stages of growth, the slopes of hills retreating to the horizon at different levels—interminable perspectives.” ”

“ The growth of a crystal is restricted like the growth of a moneron or of any cell. If the limit is passed and the conditions remain favorable to growth, we find an instance of that excessive or transgressive growth which we call reproduction in the case of living individuals. ”

“ As the waves grow when the winds strive with the other forces which govern the movements of the surface of the sea, as the heap grows when we pour corn out of a sack, as the crystal grows when from the surrounding solution the proper molecules fall into their appropriate places: so in all these cases, very much as in the organism itself, is growth accompanied by change of form, and by a development of definite shapes and contours. ”

“ Fig. 239.
If we imagine growth to act in a perpendicular direction, as for example the upward force of growth in a growing stem (OA) , then, in the absence of other forces, elongation will as a matter of course proceed in an unchanging direction, that is to say the stem will grow straight upwards. Suppose now that there be some constant external force, such as the wind, impinging on the growing stem; and suppose (for simplicity’s sake) that this external force be in a constant direction (AB) perpendicular to the intrinsic force of growth. ”

“ That there must exist a certain dependence of growth on organization, may be shown a priori. When we consider the phenomena of Life, either by themselves or in their relations to surrounding phenomena, we see that, other things equal, the larger the aggregate the greater is the needful complexity of structure.
In plants, even of the highest type, there is a comparatively small mutual dependence of parts: a gathered flower-bud will unfold and flourish for days if its stem be immersed in water; and a shoot cut off from its parent-tree and stuck in the ground will grow. ”

“ As the final result of his laborious investigations, His tells us "that a comparatively simple law of growth is the one essential thing in the first development. Every formation, whether it consist in cleavage of layers, or folding, or complete division, is a consequence of this fundamental law." ”

“ When this limit has been passed, the transgressive growth takes the form of reproduction. Every species of crystal has also a definite limit of growth; when this is passed, new crystal-individuals are formed in the mother-water on the old individual, which grows no further. ”

“ This seems in fact to be the original and primitive form of generation; and it obviously depends upon growth. Generation is the superfluity, the ὕβρις, of growth, and connects itself in the first instance with the satisfaction of hunger. First hunger, then growth, then reproduction by division or budding. And this process may go on apparently for many generations without change—in the case of certain Protozoa even to hundreds of generations. But a time comes when the growth-power and energy 7 decay, and the vitality diminishes [1] —at any rate, as a rule. ”

“ In the natural process of growth, the gap must necessarily be wider between the summits of the twigs than lower down, and, instead of imagining “missing links,” it is necessary to trace each separate branch as low down as possible, and to institute the comparisons between the lowest points that can be reached. The method is simply the logical result of the fact that every existing form of life stands at the summit of a long branch of the whole tree of life. ”

“ In a fashion similar to that manifested in the shell or the horn, we find the logarithmic spiral to be implicit in a great many other organic structures where the phenomena of growth proceed in a similar way: that is to say, where about an axis there is some asymmetry leading to unequal rates of longitudinal growth, and where the structure is of such a kind that each new increment is added on as a permanent and unchanging part of the entire conformation. ”

“ And if not, how far do differences between the surpluses determine differences between the limits of growth? We shall find, in the answers to these questions, the interpretation of many marked contrasts in growth that are not due to any of the causes above assigned. For example, an ox immensely exceeds a sheep in mass. Yet the two live from generation to generation in the same fields, eat the same grass, obtain these aliments with the same small expenditure of energy, and differ scarcely at all in their degrees of organization. Whence arises, then, their striking unlikeness of bulk? ”

“ The reader has, I hope, a clear idea by this time of the main principle of tree-growth; namely, that the increase is by addition, or superimposition, not extension. A branch does not stretch itself out as a leech stretches its body. But it receives additions at its extremity, and proportional additions to its thickness. For although the actual living shoot, or growing point, of any year, lengthens itself gradually until it reaches its terminal bud, after that bud is formed, its length is fixed. ”

“ Still, it is visible in the fact that the condition on which alone a plant can grow to a great size, is, that it shall, by the development of a massive trunk, present inner relations of forces fitted to counterbalance those outer relations of forces which tend continually, and others which tend occasionally, to overthrow it; and this formation of a core of regularly-arranged woody fibres is an advance in organization. Throughout the animal kingdom this connexion of phenomena is manifest. {147}To obtain materials for growth; to avoid injuries which interfere with growth ”

“ The fact that all living beings are developed from a minute structureless germ has long been known, while the law which governs their evolution—that the change is ever from the homogeneous to the heterogeneous—has been arrived at within a x generation. But this fact of growth is by no means limited to the physical history of plants and animals—it is exemplified upon a far more extended scale. ”

“ In all the changes of structure which regularly supervene during old age, we see the effects of deteriorated growth, and not of true development.
In the so-called process of alternate generation many individuals are generated asexually during very early or later stages of development. ”

“ Phyletic growth, or the evolution of the organic world ever into higher and more complex forms, or at least into forms of different structure, is, as I have said, merely the sum of the processes of growth of the ancestors—together with the result of external influences on the forms during their development and their existence. This additional modification which the individuals as such undergo is—together with the influence of crossing—the very cause of the constantly progressing evolution. ”

“ In seeking answers to these questions, we inquired whether there are common to both Homogenesis and Heterogenesis, any conditions under which alone sperm-cells and germ-cells arise and are united for the production of new organisms; and we reached the conclusion that, in all cases, they arise only when there is an approach to equilibrium between the forces which produce growth and the forces which oppose growth. This answer to the question—when does gamogenesis recur? ”

“ With respect to all its external relations, it must have the faculty of adapting itself, by extending its organs in one or another direction. And this adaptation is complicated by the fact that it has to be modified to meet different conditions, at different stages of development, and that the plant can flourish only when all its stages of growth are simultaneous with favoring outward circumstances, and can be completed while these continue. ”

“ Development.—Growth is increase in bulk, development is increase in structure, and Spencer's chief induction in regard to development is that we see a change from an incoherent, indefinite homogeneity to a coherent, definite heterogeneity. "The originally like units called cells become unlike in various ways, and in ways more numerous and marked as the development goes on. ”

“ In the spiral shell we have a problem, or a phenomenon, of growth, immensely simplified by the fact that each successive increment is irrevocably fixed in regard to magnitude and position, instead, of remaining in a state of flux and sharing in the further changes which the organism undergoes. ”

“ Every growing organism, and every part of such a growing organism, has its own specific rate of growth, referred to a particular direction. It is the ratio between the rates of growth in various directions by which we must account for the external forms of all, save certain very minute, organisms. This ratio between rates of growth in various directions may sometimes be of a simple kind, as when it results in the math­e­mat­i­cally definable outline of a shell, or in the smooth curve of the margin of a leaf. ”

“ And if we go back to the genesis of celestial bodies, assuming them to have arisen by Evolution, these, too, must have gradually passed into their concrete shapes through processes of growth. Growth is, indeed, as being an integration of matter, the primary trait of Evolution; and if Evolution of one kind or other is universal, growth is universal—universal, that is, in the sense that all aggregates display it in some way at some period. ”

“ During growth, which is an increase of form and structure by a succession of changes, it also exhibits a new mode of motion, which is vitality or life, and the cessation of this activity is death, when the plant returns to the geonomic world by decay. But assimilation, growth and life are continued from one generation to another, and imply time from period to period. ”

“ The direction of actual growth will be in the line of the resultant of the two forces: and, since the external force is (by hypothesis) constant in direction, while the internal force tends always to act in the line of actual growth, it is obvious that our growing organism will tend to be bent into a curve, to which, for the time being, {498} the actual force of growth will be acting at a tangent. ”

“ ANATOMICAL STRUCTURE AND GROWTH.
394. Growth is the increase of a living thing in size and substance. It appears so natural that plants and animals should grow, that one rarely thinks of it as requiring explanation. It seems enough to say that a thing is so because it grew so. Growth from the seed, the germination and development of an embryo into a plantlet, and at length into a mature plant (as illustrated in Sections II. and III.) , can be followed by ordinary observation. ”