Secondary growth

“ For normal development there must be both the growth principle and power within the individual, and the growth stimulus and materials supplied by the environment.
The rate and nature of growth and development are influenced by two factors: (1) heredity (race, family) ; (2) environment (climate, social status, economic resources, city or country, materialistic or idealistic atmosphere, commonplace or cultured, ugly or beautiful, expressive or repressive, guiding or neglectful) .
Growth and development are two different processes. Growth is increase in size ”

“ 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 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. ”

“ These facts relating to growth are of fundamental importance for a correct interpretation of the oft-discussed phenomena of early arrest of growth. We have seen that among members of the same race a prolonged period of growth goes hand in hand with unfavorable development, while an abbreviated period of growth results in larger dimensions of all physical measurements, and in a superiority of mental activity. ”

“ First, that growth being an integration with the organism of such environing matters as are of like natures with the matters composing the organism, its growth is dependent on the available supply of them. Second, that the available supply of assimilable matter being the same, and other conditions not dissimilar, the degree of growth varies according to the surplus of nutrition over expenditure—a generalization which is illustrated in some of the broader contrasts between different divisions of organisms. ”

“ These parts, then, being in close proximity with characters which neither the conditions nor correlation have affected, their suppression is naturally referred to compensation of growth. Under domestication, however, development is carried on rapidly and to a great extent. A very large number of characters is selected and developed. Here, then, we should look for the most striking manifestations of compensation of growth. ”

“ 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." ”

“ 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. ”

“ 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. ”

“ 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. ”

“ I have called this book a study of Growth and Form, because in the most familiar illustrations of organic form, as in our own bodies for example, these two factors are inseparably associated, and because we are here justified in thinking of form as the direct resultant and consequence of growth: of growth, whose varying rate in one direction or another has produced, by its gradual and unequal increments, the successive stages of development and the final configuration of the whole material structure. ”

“ 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. ”

“ But when the rate of growth is much decreased by the increase of expenditure—when the excess of assimilative power is diminishing so fast as to indicate its approaching disappearance—it becomes needful, for the maintenance of the species, that this excess shall be turned to the production of new individuals; since, did growth continue until there was a complete balancing of assimilation and expenditure, the production of new individuals would be either impossible or fatal to the parent. ”

“ 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. ”

“ Living matter is always growing, much or little, slowly or quickly, in its reserve-stuff or in its protoplasm, for expenditure or accumulation. This inevitability of growth defines it, characterizes it, and sums up its activity. Development and the evolution of growth are consequences or aspects of nutrition. ”

“ The influence of environment was demonstrated in all those cases in which changes in the rate of growth affected the final form of the body; and we saw particularly that early arrest of development does not necessarily mean unfavorable development, because in many 246cases the rapidity and short period of development seemed favorable elements. ”

“ But why should the growth of every organism be finally arrested? Though the rate of increase may, in each case, be necessarily restricted within a narrow range of variation—though the increment that is possible in a given time, cannot exceed a certain amount; yet why should the increments decrease and finally become insensible? Why should not all organisms, when supplied with sufficient materials, continue to grow as long as they live? ”

“ A complete curve of growth, starting from zero, has the same essential char­ac­teris­tics as the regeneration curve.
Indeed the more we consider the phenomenon of regeneration, the more plainly does it shew itself to us as but a particular case of the general phenomenon of growth189, following the same lines, obeying the same laws, and merely started into activity by the special stimulus, direct or indirect, caused by the infliction of a wound. ”

“ Thus, development
along lines of large growth will tend to a slow rate of
reproduction from the simple fact that unlimited energy to supply
abundant reproduction is not procurable, whatever we may assume
as to the strength or cunning exerted by the individual in its
efforts to obtain its supplies. On the other hand, development
along lines of small growth, in that reproduction is less costly,
will probably lead to increased rate of reproduction. ”

“ It may possibly be an aid to the comprehension of the process of growth to regard one factor, namely the organism, as the active side of the development tending to indefinite growth in all directions, and the other factor, the environment, as the regulating, resisting factor, limiting such growth; the conception may, perhaps, be legitimately resorted to as we resort to various other devices which bring into prominence some one side of a process to the neglect of others but to the simplification of our concepts and calculations. ”

“ He regarded the history of development as the law of growth of the organs, and, in accordance with the theory of the constancy of species, the law of growth of every species and every organ was invariable in the same sense in which we apply the term to natural laws in physics and chemistry. ”

“ The methods which shall recognize in the presence of these enormous differences of endowment the dynamic values of natural inequalities of growth, and utilize them, preferring irregularity to the rounding out gained by pruning will most closely follow that which takes place in the body and thus prove most effective. ”

“ He maintains that every thing increases as much as it can, from the lowest to the highest degree of magnitude. These principles he afterwards applies to generation, and declares that the larger sizes arise out of the lesser; that all the parts successively expand themselves, and grow and increase proportionally in the same series of time; that none of them in reality takes the start of another, so as to be quicker or slower in growth ”

“ 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. ”

“ But on the whole it may be expected that the experience of the last hundred years involves so many varying conditions that the general law of growth which satisfies that period will continue to approximate the development of the population for a considerable time to come. ”

“ 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. ”

“ It is obvious that every inch sprawled over by this trailing stem supposes all the previous inches of its lengthening course; that every successive joint implies the existence of all the earlier joints; [Pg 147] that every whorl of spines involves the development of every former whorl. Yet our reasoning is at fault; there has been as yet no succession; the development has been simultaneous, for it is the development, not of growth, but of creation. ”

“ 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. ”

“ The action in renewal, like that of original growth, may be compared—very crudely—with the action of a separator which simultaneously distributes a variety of heterogeneous materials in an orderly fashion; but in the living body the thing distributed must rather be the appetency for special materials, not the materials themselves. ”

“ In like manner we observe in the budding of a plant or animal, that a small local growth arises on a part of the mature individual, which growth becomes larger and larger, and likewise more or less separates itself from the parental organism by an independence in its growth. ”

“ Each age has its own special method of existence; thus there are laws for growth, for maturity, for decay. There are the great facts of growth by exercise or use; the necessity of maintaining a just distribution of force amongst the various parts, lest one grow at the expense of another; the alternations of action and rest required in every part of the economy; the varied life of different functions which give to each its individuality and special rule ”

“ One of the simplest cases of correlation is that a modification which arises during an early stage of growth tends to influence the subsequent development of the same part, as well as of other and intimately connected parts. ”

“ In like manner where there is homogenetic multiplication, new individuals are usually not formed while the preceding individuals are still rapidly growing—that is, while the forces producing growth exceed the opposing forces to a great extent; but the formation of new individuals begins when nutrition is nearly equalled by expenditure. ”

“ 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. ”