I have had it twice at different times and from different growers.” Similarly, the long-headed green dahlia arose twice over some years ago in the nursery of Messrs Zocher & Co. Further, the peloric Toad-flax (_Linaria vulgaris peloria_) is, De Vries informs us, “known to have originated from the ordinary type at different times and in different countries under more or less divergent conditions.” And, as this variety is wholly barren, it must in each instance have had an independent origin. Lastly, the purple beech seems to be a mutation which has originated at least three times over. Mutation Theory Criticised Every one interested in biological theory should read both _Species and Varieties_ and _Plant Breeding_ by De Vries, works which are of incalculable value to the horticulturist and agriculturist as well as to the biologist. While not wishing to detract in any way from the truly splendid work done by De Vries, we feel constrained to bring several charges against him. Firstly, he suffers from the complaint that seizes nine out of ten originators of new theories. He pushes his theory to extreme lengths; he allows his imagination to run away with him. We do not think that on the evidence available he is justified in asserting that every species passes through alternating periods of comparative quiescence and periods in which it throws off, as mutations, swarms of elementary species. He is justified in asserting that discontinuous variation is by no means an uncommon phenomenon, but further than this it does not seem safe to go at present. Secondly, he ought to lay more stress on the fact that _Oenothera lamarckiana_ is a plant which does not appear to be known in the wild state, and that it is therefore possibly a hybrid plant, and the so-called elementary species which it gives off may be merely the varieties out of which it has been built up. Boulenger and Bailey have both studied this plant, and they have not been able to witness all the mutations of which De Vries speaks, so that the former says, “The fact that _Oenothera lamarckiana_ was originally described from a garden flower, grown in the Paris _Jardin des Plantes_, and that, in spite of diligent search, it has not been discovered wild anywhere in America, favours the probability that it was produced by crossing various forms of the polymorphic _Oenothera biennis_, which had been previously introduced in Europe.” Definition of a Species