The third mutation, called Œnothera oblonga, repeatedly occurred (350 specimens) in the series of generations of Œnothera Lamarckiana that were successively cultivated. Many hundreds were cultivated later. It may be recognized with certainty as soon as the sixth leaflet unfolds, and has remained unchanged, with the exception of two specimens, which, however, have not retroceded towards O. Lamarckiana, but showed the characteristics of O. albida and O. rubrinervis. This mutation has thus, although perfectly stable, retained the power to further mutate.
The fourth mutation, Œnothera rubrinervis, again shows other interesting peculiarities. It is a strong plant, not less rich, both in pollen and in seed, than O. Lamarckiana, which was more or less the case with the other mutations. It has been obtained in very great numbers (2,976 specimens) by de Vries, and the stability of Œnothera rubrinervis has asserted itself most distinctly also for all those specimens that had descended from different mother plants.
The fifth mutation, O. nanella, differs from the others in the fact that its deviation from the original O. Lamarckiana does not show itself in a given number of sharply determined and constant characteristics, but only in one, its dwarfed dimensions. Thus we should be inclined to look upon O. nanella rather as a variety than as an elementary species. However, in this case the smaller dimensions do not come under the head of fluctuating variability, but we have undoubtedly an unmistakable mutation that can be recognized as such with certainty as soon as the second leaf begins to show itself, and which, when fecundated in 1893 by its own pollen, directly produced 440, and in 1895 2,463 germinating plants, all of them, without exception, Œnothera nanella. In 1896 the seeds of 36 other plants of O. nanella were again planted and 18,000 seedlings were obtained, which again showed, with perfect precision, the characteristics of the species, with the exception of three mutating plants that bore at the same time the distinctive characters of O. oblonga, and thus formed an elementary species of the second degree, O. nanella oblonga.
We have yet to mention two mutations, O. lata and O. scintillans. The first only consists of female plants; there is never any fertile pollen produced, so that its stability can not be made out with certainty. The second, a dark green plant with shining leaves, is a rare mutation,
- It should here be mentioned that de Vries has noticed (l. c., p. 186) that the seeds of mutating plants generally retain the power of germinating for a longer period than the seeds of the normal O. Lamarckiana. Upon this fact he bases the expectation that perhaps later it will be possible to utilize this peculiarity and to find means to increase the percentage of mutating plants in a given series of sowing experiments by artificially somewhat accelerating the dying off of the seeds. This might also prove important when searching for mutations.