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This latter hypothesis, already proposed by various authors, notably by Bateson in a remarkable book, has become deeply significant and acquired great force since the striking experiments of Hugo de Vries. This botanist, working on the OEnothera Lamarckiana, obtained at the end of a few generations a certain number of new species.
Harmless or even slightly useless ones have been seen to maintain themselves in the field during the seventeen years of my research, as proved by Oenothera laevifolia and Oenothera brevistylis. Most of the others quickly disappear. This failure of a large part of the productions of nature deserves to be considered at some length.
Oenothera albida is a very weak species, with whitish, narrow leaves, which are evidently incapable of producing sufficient quantities of organic food. The young seedling-plants are soon seen to lag behind, and if no care is taken of them they are overgrown by their neighbors.
The stems and flower-spikes and even the whole foliage were much more slender, and the calyx-tubes of the flowers were noticeably more elongated. It seems not improbable that Oenothera cruciata includes a group of lesser unities, and may prove to comprise a swarm of elementary species, while the original strain might even now be still in a condition of mutability.
In Oenothera the main stem is prolonged upwards beyond the fan; in the others the main stem is lacking or at least undiscernable, but this feature manifestly is only of secondary importance. We might even prefer the image of a fan, adjusted laterally to a stem, which itself is not interrupted by this branch. On this principle two further considerations are to be discussed.
He found a large number of specimens of Oenothera Lamarckiana growing in an abandoned potato-field at Hilversum, and these plants showed an unusual amount of variation. He transplanted nine young plants to the Botanic Garden of Amsterdam, and cultivated them and their descendants for seven generations in one experiment. Similar experiments have been made by himself and others.
It must be explained that the young plant of Oenothera has practically no stem, but a number of leaves radiating in all directions from the growing point which is near the surface of the soil. The plant is normally biennial, and in the first season the internodes are not developed.
In the case of the evening-primrose the systematic arrangement of the allied species readily guides us in the delimitations of such periods. For manifestly the species of the large genus of Oenothera are grouped in swarms, the youngest or most recent of which we have under observation.
The occurrence of new characters, or mutations as they are called, has been specially studied by other investigators, and I propose briefly to consider the two most important examples of such research, namely, that by Professor T. H. Morgan, which deals with the American fruit-fly Drosophla, and the other which concerns the mutations of the genus of plants OEnothera, exemplified by our well-known Evening Primrose.
This form is met with in different parts of France, while the biennis and muricata are very common in the sandy regions of Holland, where I have observed them for more than 40 years. They are very constant and have proven so in my experiments. Besides these three species, the large-flowered evening-primrose, or Oenothera lamarckiana, is found in some localities in Holland and elsewhere.