Part 4

For the examination of idioplasmic differences we are restricted to visible characters. Hence a knowledge of the nature of an organism presupposes a complete investigation of its characters in their succession during the whole ontogeny. The results must, however, be tested and completed by comparison with other organisms and by the most comprehensive experimental procedure, possible, (as by culture under various conditions, and crossing with nearer and more remote relatives). The characteristics of nutrition varieties and accidental crosses must be separated from specific characteristics by experimental procedure, and latent determinants must be brought out by the same means.

15. REPRODUCTION, AND RELATION BETWEEN PARENTS AND OFFSPRING.

Reproduction is nothing more than a transition from one generation to the next following, mediated by the idioplasm of the germ cell. In asexual (monogenic) reproduction there is continuity of the same idioplasm. Therefore the parent continues in the offspring its specific life, as the stem continues its specific life in the branch. All the peculiarities conditioned by the idioplasm remain unchanged in the offspring. The latter, as the immediate continuation of the preceding ontogeny, starts from the point at which the germ cell left it, so that immediately after the germ cell is separated at the close of the ontogeny or before, the offspring passes at one time rapidly through the whole ontogeny, at another only the remainder or a part of it (the latter in alternation of generations and in asexual propagation of phanerogams).

In sexual (digenic) reproduction the formation of the germ cell is brought about by the union in equal parts of both parental idioplasms. The offspring is the organism resulting from the union of the force and matter of the parents, and represents in its nature the united continuation of their ontogenies. The characteristics of development of the child depend however on the viability of the determinants of the mingled idioplasms in which a new equilibrium has been formed. Hence if the child bears more resemblance to the father or to the mother, it follows that some of the inherited determinants develop while the others remain latent. If the child has certain visible characteristics more marked than either parent, it becomes possible only by the development of determinants which had previously been latent. The fact that the mother furnishes the germ cell with nutritive plasm and that she nourishes it for a considerable time does not increase the number of maternal determinants nor their capability of development.

If two corresponding characters, one derived from the father, the other from the mother, come into conflict in sexual reproduction, the one or the other, or even a third alternative characteristic, which heretofore was present as a latent determinant, may develop in the child. But also both parental characters may appear at once and in various combinations. Whether the development follows in the one way or the other depends on the strength of the individual determinants, on the kind of their idioplasmic arrangement, and on their agreement with the nature of the newly formed idioplasm.

16. HEREDITY AND VARIATION.

If heredity and variation are defined according to the true nature of organisms, they are only apparent opposites. Since idioplasm alone is transmitted from one ontogeny to the next following, the phylogenetic development consists solely in the continual progress of the idioplasm and the whole genealogical tree from the primordial drop of plasma up to the organism of the present day (plant or animal) is, strictly speaking, nothing else than an individual consisting of idioplasm, which at each ontogeny forms a new individual body, corresponding to its advance.

In this idioplasmic individual the automatic or perfecting variation is always active, so that the idioplasm of a phylogenetic line always grows by propagation of the determinants contained within it, as a tree grows larger through its whole duration of life by branching. On the other hand the adaptation variation caused by external stimuli is present only in those periods of the phylogenetic line in which the idioplasm, and together with this the individual, do not possess the obtainable maximum of adaptation to their environment for the time being. Both of these variations of the idioplasm take place so slowly that only after a long series of generations do the new determinants become capable of developing and revealing themselves in the transmutation of visible characters.

Aside from the phylogenetic variations already named, which take place according to the measure of ontogenetic growth, the idioplasm undergoes, as a result of crossing, as well as in changes of the ontogeny, gamogenic variations which may be designated as stationary, since in the mingling of sexually different idioplasms there arise only new arrangements of determinants already present, but no new formation of determinants takes place. Hence in this way arise also new combinations of developmental characteristics.

As a result of external injurious influences, abnormal variations, or pathological variations, appear in the idioplasm. These consist of disturbances of equilibrium, which take place also without new formation of determinants. Thereby the determinants already present are caused to develop in abnormal relations, and mostly in reversions.

Apart from the inheritable variations of the idioplasm just enumerated, and the transformations of visible characters involved in it, the soma-plasm and the non-plasmic substances experience, by the influence of nutrition and climate, greater or less variations, which constitute nutrition varieties, and since the idioplasm remains unaffected in general, last only so long as the causes which called them forth.

Naegeli, like Weismann, arrives at the conclusion that acquired characters are not inherited. He was not content, however, to rest the generalization upon purely speculative grounds, but undertook the experimental demonstration. After seventeen years of work by himself and son, especially upon several species of Hieracium, he satisfied himself that his theory was true to the facts. We all know now how far he fell short of settling the question.--Trans.

If we have in mind the inner nature of the organism, there is, properly speaking, no such specific phenomenon as heredity, since the phylogenetic line is a continuous idioplasmic individual. In this sense heredity is nothing more than the persistence of organized substance in a movement in which variations are automatically induced, or the necessary transition of one idioplasmic configuration into the next following. It is present, not only among plant and animal individuals which are ontogenetically separated, but also everywhere within these individuals, where individual parts (cells, organs) follow each other in time. Hereditary phenomena are those that necessarily pass over to following generations, and in general those that are located in the idioplasm, since non-idioplasmic substance can be hereditary only through a limited number of cell generations.

Variations and heredity are generally estimated, not according to the inner nature of the mature individuals, but according to their relation in successive generations, since heredity is assumed when the ontogenetic characters remain the same, and variation when previously latent characters become visible. But these phenomena belong to another department of science; they concern the possibility and reality of development of the idioplasmic determinants.

17. VARIETY, RACE, MODIFICATION.

From the multifarious variations of organisms proceed various categories of kinship. Varieties arise by extremely slow changes in the idioplasm due to the perfecting process and adaptation. Since these are conditioned by the same causes, they follow in all individuals of the same variety in uniform manner. Varieties are uniform, entirely constant under the most various external conditions, in general cross only with difficulty with related varieties, are not varied by accidental crosses, and persist through geological periods. Varieties belong to feral nature rather than to culture; they can assume all possible modifications without injury to their specific characteristics, but can show no distinctions of races, for all beginnings of race formation are destroyed by free intercrossing. They differ from species only in that they are to be designated as more closely related species, or species as more remotely related varieties. Every other distinguishing characteristic is wanting.

Races arise from gamogenic or pathological variations of the idioplasm. In the former case they presuppose crossing between related varieties or species, in the latter case an increased sensibility and weakening of the idioplasm. Very often both causes co-operate, since crossing follows more easily when the idioplasm is weakened by hurtful influences and since the irritability and weakening of the idioplasm increases if crossing has preceded. Race formation begins in single individuals. Among several individuals it begins in various directions because the causes are different and hence may display a great multiformity. Races are distinguished by more or less abnormal characteristics; they arise quickly--often in a single generation--and present various degrees of stability. This stability is insured to some extent only by the strictest in-and-in breeding. All races disappear through crossing, likewise many races that have arisen from pathological variations disappear even in sexual reproduction (in self-fecundation). Races belong exclusively to cultivation, where they can develop and exist protected from free intercrossing.

While varieties and races arise by progressional or stationary variation of the idioplasm, modifications are produced by such influences of nutrition and climate as act only on the soma-plasm and the non-plasmic substances, and hence do not give rise to inheritable characters in the organism. Modifications persist only so long as their causes, and under other environments immediately pass over into the modifications corresponding to them. The transition is completed in the lowest plants during a limited number of cell generations; in an individual of the higher plants on the same stem during the growth of a single year. Each variety and each race appears clothed in a definite modification, and can change it within a range peculiar to itself.

The distinctions which Naegeli here erects are, of course, purely arbitrary, and his definitions are suitable for use only in his own thesis.--Trans.

18. SOCIAL AND INDIVIDUAL ORIGIN OF SPECIES.

The species arises neither from the nutrition variety nor from the race; it is always a more advanced variety, and hence species formation is identical with variety formation. Cause for variation and consequently for variety formation is always shown, either when, environment remaining the same, the automatic variation of the idioplasm has advanced so far that the ontogeny is raised to a higher grade of organization and division of labor, or when external stimuli act for a sufficiently long time in a manner not in harmony with the previous adaptation. Hence various varieties arise easily from a uniform kinship, when these are thrown among unlike external influences by local separation, because in the separated places on the one hand the automatic evolution proceeds with unequal rapidity, and on the other hand adaptation takes place unequally.

But in general different varieties arise socially from a uniform kinship. This is because the related individuals living together are unequally stimulated on account of the great inequality of external influences which may exist at the smallest distances; and also because with slight individual differences unlike reactions often follow upon the same external influences. If identically similar individuals are equally inclined to very different reactions toward the same stimulus, sometimes the direction of the first variation decides the character of the adaptation and therefore the nature of the variety, because the variation, when once begun, progresses unswervingly even under somewhat different circumstances. Hence divergent variations are found growing together in all places, which variations have begun at different though neighboring points by transformation of the idioplasm and are soon intermingled on account of the easy dissemination of seed.

It is interesting to compare this statement with Weismann's recent theory of Germinal Selection.--Trans.

The social formation of varieties is not in general interrupted by crossing, a process which governs only the formation of races. It is confirmed according to experience by the universally recurring fact that several beginnings of the most closely related varieties appear together not only in the same region, but even at the same points, while the geographical distribution of the more marked varieties and of related species offers no conclusion as to their origin, but only as to the last great migration of the plant world, because they arose before this period, as indeed appears from their distribution.

Just as different varieties arise simultaneously from one kinship at the same place, the same variety may arise in places far separated, when the analogous external exciting causes occasion an identical transformation in the idioplasm. The experimental proof lies in the fact that like beginnings of varieties often appear at great distances from each other.

An apparent social origin of varieties is indicated, when, after having come together in migration, they first develop the unlike determinants which they have gained in various locations. An apparently individual origin of the same or different varieties is indicated, when the formation of the determinants take place at one and the same place, but their development follows only after the kindred has been scattered by migration.

19. GENERAL RELATION OF THE PHYLOGENETIC LINES IN THE ORGANIC KINGDOMS.

Since the nature of an organism is contained in the sum of its idioplasmic determinants alone, the evolution of a phylogeny consists in the evolution of the idioplasm. This is perceived from the succession of the visible ontogenetic characteristics which in general run parallel with it. The idioplasm varies in two ways: (1) by an automatic perfecting process; (2) by adaptation to environment.