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.[H] 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.

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.

By virtue of the automatic variation of the idioplasm the ontogenies of a phylogenetic line attain to a continually more complex organization and greater differentiation of function. In this differentiation, however, only the qualitative differences are of importance; quantitative and numerical gradations may be disregarded. The more complex admits of more combinations than the simpler; hence if a phylogeny reaches a higher stage by automatic evolution it may branch into several lines, of which each appears as the continuation of the parent stock.

Since adaptive variations depend only on the transmutations of environment, an organism may rise to a higher organization and division of labor by continually adapting itself to the changed environment. But the organism may also change its adaptation while it remains at the same stage of organization. And since the adaptive variation is quickly perfected as compared with automatic evolution, although extremely slowly as compared with the duration of the ontogeny, an organization may change its adaptation several times while it remains at the same grade of organization and division of labor. Since there are also numerous different kinds of adaptation, a phyletic line may divide at each point into several adaptive forms, which appear in the taxonomic system as species, genera, often even as whole families, while in other cases various degrees of organization have appeared in one family.

20. LAWS OF EVOLUTION OF THE PLANT KINGDOM.

In the sub-organic kingdom, which precedes the plant and animal kingdoms, (see page 5), there are gradually formed from the spontaneously generated plasma independent cells with their characteristic properties, i.e., growth by intussusception of micellæ, formation of a plasmic cuticle, and a non-plasmic membrane about the same, division of the cells, separation of the cells thus formed, and free cell formation within the cell contents. These properties are inherited from the sub-organic kingdom by the plants and animals which follow in the next stage of phylogeny. The evolution of the plant kingdom proceeds through the following regular processes, which continue to operate through the entire phylogenetic series.

Law of Phylogenetic Combination.—The simplest of all plants are cells of round form, which grow and reproduce themselves by division, budding or free cell formation. From the fact that the younger generation of cells, instead of separating from each other and growing to independent plant individuals, remain united with each other, multicellular plants arise from unicellular. The same transformation of the reproductive cells into non-separable tissue cells is repeated several times in multicellular plants and serves to enlarge the individual. There is manifested in this phylogenetic process the tendency of the plant to combine in the higher stages into one complex whole those parts which in the lower stages tend to be independent. A similar unifying tendency is revealed also in those plant members which have arisen by differentiation and represent a system only by their being connected at certain points. These combine in the higher stages and form ultimately continuous tissues.

Law of Phylogenetic Complication or Ampliation, Differentiation and Reduction.—The cells, and, in general, the parts of plants which lie near each other in space or follow upon each other in time, are always alike in the lower stages. By differentiation they become unlike, so that the sum of the functions which at first fall to the lot of all parts without distinction now is shared among the individual parts. By this means each part can perform its own special function so much the better. Differentiation is repeated in the course of the phylogeny, since at first all parts of an ontogeny diverge into two or more parts, then the parts of these parts divide again, etc. Along with this process of division another process is always active, which, as it were, prepares the way for the former, namely, ampliation, by virtue of which the growth of the whole ontogeny or of single stages of it undergoes a quantitative increase, so that an organ acquires a greater number of cells, and an individual a greater number of organs. After this increase in