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New elementary species are far more rare, but I have discovered in the great evening-primrose, or Oenothera lamarckiana a strain which is producing them yearly in the wild state as well as in my garden. These observations and pedigree-experiments will be dealt with at due length in subsequent lectures.
Partly so by the morphologic peculiarities of lamarckiana, which seem to exclude red flowers, composite leaves, etc. No doubt there are more direct reasons for these limits, some changes having taken place initially and others later, while the present mutations are only repetitions of previous ones, and do not contribute new lines of development to those already existing.
It is quite obvious that Oenothera lamarckiana was in a mutating condition when I first saw it, seventeen years ago. How long had it been so? Had it commenced to mutate after its introduction into Europe, some time ago, or was it already previously in this state? It is as yet impossible to decide this point.
It might be supposed that on closer inspection each mutation might be brought into connection with some feature of the fluctuating variability. But this is not the case. The dwarfs are not at all the extreme variants of structure, as the fluctuation of the height of the lamarckiana never decreases or even approaches that of the dwarfs. There is always a gap.
Moreover I observed that the attributes of lata and nanella, which I now studied in the offspring of my first mutants, were clearly discernible in extreme youth, while those of rubrinervis remained concealed some weeks longer. Hence I concluded that the young plants should be examined from time to time until they proved clearly to be only normal lamarckiana.
Hence there can be little doubt that the unpaired units are the cause of this decrease in reproductive power. The genus Oenothera is to a large degree devoid of varietal characteristics, especially in the subgenus Onagra, to which biennis, muricata, lamarckiana and some others belong.
I made a pedigree-culture of lata during eight successive generations, pollinating them in different ways, and always obtained cultures which were partly constituted of lata and partly of lamarckiana specimens. But the latas remained lata in all the various and most noticeable characters, never showing any tendency to gradually revert into the original form.
Plants from the Northeastern American seaboard, identifiable with the species do not entirely agree with those raised from seed received from Holland. O. lamarckiana has not been found growing wild in America in recent years although the evidence at hand seems to favor the conclusion that it was seen and collected in the southern states in the last century. Publication 24. Carnegie Institution.
In this the normal lamarckiana was the main line, and seeds were only sown from plants after sufficient isolation either of the plants themselves, or in the latter years by means of paper bags enclosing the inflorescences. I have given the number of seedlings of lamarckiana which were examined each year in the table below.
We should thus arrive at a demonstration of what Eimer called orthogenesis, or evolution in definite directions. The mutation lata cannot be said to breed true, as the pollen is almost entirely sterile. It has therefore been propagated by crossing with Lamarckiana pollen, with the result that both forms are obtained with lata varying in proportion from 4 per cent. to 45 per cent.
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