Truth and Error or the Science of Intellection/Chapter 6

by John Wesley Powell

CHAPTER VI

GENERATIONS OR PROPERTIES OF PLANTS

We are yet to follow properties through higher degrees of relativity. For this purpose it becomes necessary to examine the relations exhibited by plants in metabolism, growth, vitality, and heredity. Plants are not wholly disparate bodies, but rise by a discrete step or degree in relativity not exhibited in ethronomy, astronomy and geonomy. So that not only are the properties in those realms found in this new realm, but in addition a new set of relations which we denominate generations. We have, therefore, to examine those characteristics by which plants are distinguished from geonomic bodies, of course in only a general and summary manner.

In plants new kinds appear by chemical recomposition. A new substance, protoplasm, is constituted, being organized of many molecules of different kinds, which again combine with other substances. These molecules seem to be still further arranged in different proportions, by which the new plant substances become many; the formation of these substances is called assimilation.

The many substances of plant tissue have a secular development which is growth in size and form. The period of existence of the plant body is limited, and at death returns to simpler conditions; this return is decay, and belongs to the grade of processes. In growth the plant undergoes a change of increasing relativity, and in decay returns to a simpler state of relativity.

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. This time is occupied in making changes, and causation is metagenesis. Now a new element of time appears, for by producing germs and thus multiplying individuals like itself the same stages of metabolism, growth and life observed in the parents are repeated in the offspring. This new element is heredity, in which the offspring inherits the potentiality of the parent as it is restricted within certain narrow limits to careers of metabolism, growth and vitality similar to that of the parent.

Thus generations are generations of processes. The processes are assimilation, construction and destruction, growth of form and structure, vitality exhibited in endosmosis and exosmosis, and finally processes are repeated by heredity represented by parents and children.

In this grade of concomitants it must be observed that there can be no assimilation without growth, no growth without vitality and no vitality without heredity.

Indeed, as we go on to contemplate the concomitants that appear by increasing relations, it becomes more and more evident that one cannot exist without the others, and that abstraction must always be distinguished from analysis. It becomes possible to treat the whole process of plant formation as assimilation or as growth or as life or as heredity, and yet we distinguish these concomitants in thought. If we treat of the assimilation of plants, the phytology of plants, the vitality of plants or the heredity of plants through germs, we seem to take the whole subject in view, for the concomitants are not disparate but only abstract in consideration.

II

I define constructive assimilation as the building up of protoplasm, a compound composed of many molecules, and I define differentiating assimilation as the recombination of protoplasm into other substances which are simpler compounds. These simpler substances are composed not only of some of the molecules of protoplasm itself, but also of other substances, and are used for various purposes in the economy and structure of the plant. In these recombinations a surplus of substance is found which is excreted by the plant in two ways: first, as water which is imbibed and used as a vehicle for other substances, for the amount of water is in excess of the amount ultimately used in the tissue of the plant, and is excreted by transpiration; and second, as carbon-dioxide, for the oxygen of the air unites with an excess of carbon, and it is then excreted by respiration. Thus protoplasm is the basis of the tissues of the plant; but to make these tissues it must be recombined into different substances which are newer compounds, and new substances not found in protoplasm are necessary therefor. The water which is necessary for protoplasm is furnished together with an additional amount which becomes the vehicle for the new substances, and the surplus is excreted. In the building of new substances oxygen from the air is needed to dispose of some of the carbon, and this office is accomplished by respiration. Imbibition of water by the roots furnishes the material for assimilation both constructive and differentiating, while respiration in the leaves furnishes the oxygen necessary for certain chemical changes. We must now consider the substances produced by assimilation.

The plant is a chemical laboratory of exceeding complexity, where all of the operations are carried on with marvelous deftness and delicacy, and with a system of chemical paraphernalia adapted to the operations of microscopic life. The entire plant is engaged in these operations as long as life lasts, sleeping in partial rest by night and hibernating in semi-torpidity during the winter, but carrying on its operations in full vigor when the sun is genial. Assimilation deals with particles so minute that even the eye of the microscope cannot see them, and they can be known only when aggregated in masses as material for use or as products, but the operations are carried on particle by particle in such a manner that what is and what becomes reveal the method of becoming only to the eye of reason; thus ultimately all chemical knowledge is the product of inference. Nevertheless this inferred knowledge is erected upon a foundation of consciousness as revealed by the senses, and the ultimate proof of the validity of the inferences is the multiplication of facts as they are accumulated in vast numbers by history and attested by the verification of prophecy; finally, as the facts are resolved into laws their congruity is made evident. The love of truth born of the generations of thinking minds forever engaged with the materials of consciousness in the process of inference, ultimately establishes a habit and love of truth that submits every judgment to the tribunal of congruity, the court of equity which every man erects in his own soul. This is the supreme court of judgment.

History may decide and prophecy may confirm, but these decisions are annulled if the court of congruity finds them contradictory. Experience in the laboratory may pile up facts, prophecy in the laboratory may be fulfilled in multitudinous cases; but under the decrees of the court of congruity if any incongruity appears the chemist is turned again to his experiments, resting assured that somewhere his facts or theories are wrong, and he plunges into his labors to reach peace only when congruity is found. To a man who has not devoted his life to chemical research and has familiarized himself only to a limited extent with the history and theories of chemistry, the vast body of experiments, the innumerable verifications of prophecies and the congeries of congruities which have developed since Dalton propounded the atomic theory are such a monument of accomplishment by inference and verification that they appear as a pyramid of truth.

The fact to which especial attention is called is this: That the laboratory reveals in the substances of plants innumerable new kinds and these new kinds are found in series.

III

The plant is a laboratory for the evolution of many substances; but as the particles of which they are composed have number and as they are arranged in numerical, that is, molecular orders, they have at the same time extension, and their arrangement implies that they are placed in forms. Thus having considered generations of kinds, we are led to the consideration of generations of forms, and the forms which we have to consider are forms of cells, forms of tissues, forms of phytons and forms of plants. Plants also exhibit forms of crystals; the crystallization is fundamentally a theme of geonomy, so on the very start of this subject we are confronted with the fact that the plant exhibits the concomitants of lower relativity, but for present purposes we may neglect them.

The normal and developed cell has three concentric envelopes which may be called blasts, the whole enclosing a nucleus, so that the structure which we found in the earth as spheres is repeated here as blasts. These are the exoblast, mesoblast, and endoblast. Some plants are single cells, other plants are aggregates of loosely attached cells joined together as threads or as webs of threads as in the slimes, but in plants of a little higher grade these webs are consolidated by a woof of plant tissue as in some of the lichens and seaweeds.

The tissues are consolidated and modified cells. Then tissues are differentiated, exhibiting different structures; different structural tissues are again related and modified for the performance of functions as phytons and the phytons are systematized to constitute the plant, but the phytons are differentiated for special functions and we have the roots for imbibition, the leaves for respiration and transpiration, the circulatory apparatus for transportation, the floral phytons for reproduction and the protecting apparatus for the external covering of plants.

A system of phytons constitutes the higher plants. In the history of plant life the morphology of plant phytons is an important part of the science of botany, for the forms of phytons undergo a succession of changes, the investigation of which vies in importance with that of the chemical development of kinds to which we have heretofore alluded. When the different classes of plants are examined in this respect, the succession appears in the development of classes, those plants of the lower classes passing through morphologic stages which are repeated in higher classes and continued to still higher stages, so that the plants of the highest class practically include all of the stages in succession as exhibited in the order of the lower classes. While some research has been devoted to this subject, much more requires to be done.

IV

That which we call chemism is one of the concomitants of process and is here transmuted into vitality. Vitality is chemism internally controlled by the plant in obedience to the laws of heredity, and externally controlled by heat, gravity, and strain which produces stresses. Thus vitality is a new mode of motion. We must here remember that motion as speed is inherent and constant in the particle and that motion as path is always determined from without, but the particles within the body are all external to one another, and therefore the direction of motion which is internal to the body is in obedience to the laws of heredity, and the direction of motion which comes from without the body is heat, gravity and strain. Heat and its modification as light and perhaps as electricity and magnetism play an important role in vitality, which has been subject to much investigation by the observation of nature and artificial experimentation. The vitality of the plant is accelerated by heat, and becomes torpid when it is insufficient. Certain chemical processes, like that of the production of chlorophyll, are dependent upon light. Doubtless gravity exerts a direct influence upon the functions of the plant, but this influence has had inadequate examination. Stress and strain are exhibited as endosmosis and exosmosis, exhibited to us in the circulation of fluids through the membranes of the cells, and is an important theme in the physiology of plants.

V

As the plant germinates the motions of its particles in change are directed by the preexisting constitution of the germs; assimilation, therefore, is a directed motion, and as changes in assimilation and growth proceed the continued motion of vitality is controlled by antecedent conditions. In this manner the plant must pass through the same phases of assimilation and growth through which the parent proceeded; thus conditions are imposed which constitute causation; but there are other causes than those inherited, for the germ may not grow at all; it may not get footing in the soil, it may not find sufficient moisture, or the moisture may not contain other necessary ingredients. When it starts the frost may nip it, the sunlight may fail it because of an overhanging shade, herbivorous animals may devour it, man may dig it up. All of a multitude of conditions are necessary that a plant may mature; and these causes may be traced to the ultimate supply of food, as effecting the assimilation, to external forms which cast destructive shadows or protect from destruction, or they may be traced to external forces, so that there are heredity conditions and environmental conditions.

The plant is thus subject to inexorable conditions by its inheritance, and these conditions restrict its growth to the course pursued by its ancestors; but heredity is not the only factor of causation involved; the environmental factors may succeed in preventing, arresting or modifying the development of the plant. When the plant arrives at maturity and produces other germs, they also are subject to the laws of heredity; but the inheritance which they receive has accumulated in the development of the parent. Thus as generations pass there is secular development.

VI

Metabolism implies affinity, and again we have the problem of its nature in plants. It has often been surmised, and sometimes taught, to be choice. It seems to be the same thing in plant life, but there are other phenomena which appear in plants which suggest that the ultimate particles have not only the power of choosing their atomic and molecular associates, but they also seem to have the power to a limited degree to choose the attitude of their phytons toward external objects in space. Thus certain phytons seek the soil where they may perform the function of roots, and others seek the air where they may perform various functions in the plant life. These subaërial phytons seem to be able to direct their course toward different objects, when they require support, as in the case of climbing plants, and the leaves seem to be able to open or close in order to adjust themselves to conditions of light and darkness. The investigations into these functions of the plant are numerous and interesting, but they have been pursued mainly with the purpose to account for them as of a mechanical nature. Yet the problem remains: Have the plant elements the property of choice? If they have such a property they must also have consciousness.

We find in plants the same essentials: unity, extension, speed, and persistence as they are compounded into the properties of number, space, motion, and time, and as they are further developed as time, form, force, and causation; we also find the fifth property of affinity, which now seems to be choice even more plainly than we have found it in other bodies.