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Updated: June 23, 2025
Other proofs could be given by other biennials, and among them the stray annual plants of common carrots are perhaps the most notorious. In my own cultures of evening-primroses I have preferred the annuals and excluded the biennials, but without being able to produce a pure annual race. As soon as circumstances are favorable, the biennials return in large numbers. Cereals give analogous proofs.
If the plant fertilizes itself without the aid of insects, as do some evening-primroses, the seed saved from the native locality may prove wholly pure, and if it does give rise to a uniform progeny the constancy of the race may be assumed to be proved, provided that repeated trials do not bring to light any exceptions.
But the evening-primroses open their anthers in the morning, fertilize themselves during the day, and only display their beautiful flowers in the evening, after the pollination has been accomplished. They then allure evening moths, such as Agrotis and Plusia, by their bright color, their sweet honeysmell and their nectar.
This is at once manifest, if we compare the group of new mutants with the swarms of elementary forms which compose some of the youngest systematic species, and which, as we have seen before, are to be considered as the results of previous mutations. The difference lies in the fact that the evening-primroses have been seen to spring from their ancestors and that the drabas have not.
The present mutable state must then have been preceded by an immutable condition, but of course thousands of mutations must have been required to produce the evening-primroses from their most remote ancestors. If we take the species into consideration that are not mutable at present, we may ask how we are to harmonize them with each of the two theories proposed.
Hence we should conclude that when a species is converted into a new type in one locality this is only to be considered as one of numerous possible ones, and its alteration would not in the least change the aspect of the remainder of the species. But even with this restriction the general belief is not supported by the evidence of the evening-primroses.
Is the mutability of our evening-primroses temporary, or is it a permanent condition? A discussion of this problem will give us the means of reaching a definite idea as to the scope of our inquiries. Let us consider the present first. If mutability is a permanent condition, it has of course no beginning, and moreover is not due to the agency of external circumstances.
Somewhere no doubt the desired principle lies hidden, but until it is discovered, all methods must be tried. With this conception as the best starting point for further investigation, we may now make a brief survey of the other phase of the problem. We shall try to connect our observations on the evening-primroses with the theory of descent at large. We start with two main facts.
Summing up the results of this discussion, we may justifiably assert that the conclusions derived from the observations and experiments made with evening-primroses and other plants in the main agree satisfactorily with the inferences drawn from paleontologic, geologic and systematic evidence. Obviously these experiments are wonderfully supported by the whole of our knowledge concerning evolution.
Today I have only to show that the mutations of the evening-primroses, though sudden, comply with the demands made by Darwin as to the form of variability which is to be accepted as the cause of evolution and as the origin of species. Some of my new types are stouter and others weaker than their parents, as shown by gigas and albida. Some have broader leaves and some narrower, lata and oblonga.
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