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It must be a very curious combination of the unit-characters which causes such a state of continuous variability. The pure quality of the species must be combined with the peculiarity of the variety in such a way, that the one excludes the other, or modifies it to some extent, although both never fully display themselves in the same part of the same plant.
Systematic atavism by this means leads us to a closer examination of the internal and concealed causes, which rule the affinities and divergencies of allied species. It brings before us and emphasizes the importance of the conception of the so-called unit-characters. The primrose will serve as an example.
Dick, himself talking, in cool sentences amplifying his thesis, apparently engrossed in his subject, saw Paula make the aside, although no word of it reached his ears, saw her increasing nervousness, saw the silent sympathy of Graham, and wondered what had been the few words she uttered, while to the listening table he was saying: "Fischer and Speiser are both agreed on the paucity of unit-characters that circulate in the heredity of the lesser races as compared with the immense variety of unit-characters in say the French, or German, or English...."
This pathway is to be laid out with regard to the following considerations. We are not to cross species or varieties, or even accidental plants. We must cross unit-characters, and consider the plants only as the bearers of these units.
But to enlarge the range of the varieties this simple and stable form would need to be treated anew, by crossing it with the parent-types. Such experiments however, have miscarried owing to the too stable nature of the unit-characters. This stability and this absence of the splitting shown by varietal marks in the offspring of hybrids is one of the best proofs of unisexual unions.
For myself I have based my field-researches and my testing of native plants on the hypothesis of unit-characters as deduced from Darwin's Pangenesis. This conception led to the expectation of two different kinds of variability, one slow and one sudden. The sudden ones known at the time were considered as sports, and seemed limited to retrograde changes, or to cases of minor importance.
True elementary species differ from each other in a number of unit-characters, which do not contrast. They have arisen by progressive mutation. One species has one kind of unit, another species has another kind. On combining these, there can be no interchange. Mendelism assumes such an interchange between units of the same character, but in a different condition.
It's a long, long way to the day of a segregating out and in of Mendelian unit-characters. Besides, this is a strange world of choices. Nobody is to be considered worthy of parenthood until he has fallen in love properly. Nobody who would permit an outsider's decision as to when he was properly in love would be worth thirty cents as a parent.
We may call these innermost representatives of the unit-characters pangenes, in accordance with Darwin's hypothesis of pangenesis, or give them any other name, or we may even wholly abstain from such theoretical discussion, and limit ourselves to the conception of the visible character-units. These units then may be present, or lacking and in the first case active, or latent.
The conception of mutation periods producing swarms of species from time to time, among which only a few have a chance of survival, promises to become the basis for speculative pedigree-diagrams, as well as for experimental investigations. The principle of unit-characters and of elementary species leads at once to the recognition of two kinds of variability.
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