learn to analyze the elements of the phenomenon, the probability grows that sometime we shall master the art of actually directing the series of natural phenomena. A new and limitless field of work would then be opened. Provisionally we can guess only from what we have as yet observed that certain processes are able to call forth or to accelerate the phenomena of mutation. Thus de Vries suggests the idea that a rapid succession of periods of reproduction might facilitate the reappearance of a period of mutation, whilst others think that transportation into quite different surroundings or transplantation might produce it. Others, again, appear to believe that increased nutrition, either combined with the conditions mentioned or not, would call forth mutation. All this, however, is no more than guesswork and hypothesis. We have as yet no means of fully knowing and of understanding.
For the present it is safer to recognize our absolute ignorance, and at the same time to define more exactly how far de Vries has brought us, and what is the important step for which we have to thank him. We can warmly recommend the reading and studying of de Vries 's clearly written and beautiful book. He has been the first to show us the sharp distinction that exists between chance variation and fluctuating variation, and to prove that it is not the latter, but the former, that calls forth in nature the origin of species. He has not yet been able to tell us whether, and, if so, how, chance variation could be called forth artificially by man. The fact that artificial selection of fluctuating varieties, as well as hybridizing, etc., has already led to such indisputable improvements in the different races of animals and plants may, however, give us hope that a conscientious experimenter and close observer, such as de Vries, has still a full store of important pioneer's work before him and may yet succeed in finding how to direct the mutation process. Thus, the origin of species would not only have been studied more closely, but would be subjugated to the human will. After having seen species originate in nature, man would then be able to call them forth. Then only the 'Origin of Species,' to which Darwin has given us such a marvelous introduction, would be revealed in all its details.