MSS intended for publication and books, etc., intended for review should be sent to the Editor of THE AMERICAN NATURALIST, Garrison-on-Hudson, New York. Articles containing research work bearing on the problems of organic evolution are especially welcome, and will be given preference in publication. One hundred reprints of contributions are supplied to authors free of charge. Further reprints will be supplied at cost. Subscriptions and advertisements should be sent to the publishers. The subscription price is four dollars a year. Foreign postage is fifty cents and Canadian postage twenty-five cents additional. The charge for single copies is thirty-five cents. The advertising rates are Four Dollars for a page. Lancaster, Pa. THE SCIENCE PRESS NEW YORK: Sub-Station 84 Garrison, N. Y. Entered as second-class matter, April 2, 1908, at the Post Office at Lancaster, Pa., under the Act of Important New Scientific Books Botany PUBLISHED BY THE MACMILLAN COMPANY The Origin of a Land Flora. A Theory based upon the facts of Alternation. Cloth, gilt top, xi+727 pp., illus., index, 8vo, $5.50 net. NOTE.-A profound study in the morphology of the lowest forms of plants, with special reference to the development of their reproductive systems. The author endeavors to show that the present land flora has originated from an aquatic ancestor, and traces the methods of specialization to the land habit, and the establishment of the forms of the higher plants. A book of the highest importance not only to botanists but to biologists in general. NEW AND STANDARD HAND-BOOKS ON AGRICULTURE, ETC. Cloth, xvi+829 pp., illus., appendix, glossary, index, 12mo, $.75 net. NOTE. This is a thoroughly modern treatise on farming as practiced in the Gulf States, from the point of view of the scientific agriculturist. It is adapted to school use, but is of practical service to any farmer in that part of the country. The author is vice-director of the Texas Experiment Station. Re-issues of the highly valued Hand-Books known as the Garden Craft and Rural Science Series, edited by L. H. BAILEY, of Cornell University, Editor of "Cyclopedia of American Horticulture," "Cyclopedia of American Agriculture," etc. The Principles of Fruit Growing. By L. H. BAILEY. Tenth Edition, $1.50 net, by mail $1.66. Irrigation and Drainage. By F. H. KING. Fifth Edition, $1.50 net, by mail $1.68. Principles of Vegetable Gardening. By L. H. BAILEY. Bush Fruits. By FRED W. Sixth Edition, $1.50 net, by mail $1.68. Fertilizers. By EDWARD B. VOORHEES. Tenth Edition, $1.25 net, by mail $1.38 Farm Poultry. By GEO. C. WATSON. Sixth Edition, $1.25 net, by mail $1.42 Published The Macmillan Company By 64-66 5th Ave., New York IT is a well-established fact that what are commonly called variations include modifications of quite different import in relation to the process of evolution. Whether or not the variations that are induced in the soma, either by its own activities or through the influences of the environment, have any effect in shaping the course of evolution as they were held to do by Lamarck and his followers, it is evident that they do not count in this process in the same way as variations that arise in the germ. But among the germinal variations themselves there are classes of unequal significance. Variations differ markedly in regard to their stability or permanence. Many variations after their first appearance persist with little modification for an apparently indefinite time. Of these what are commonly called mutations afford conspicuous examples; these are abrupt variations which breed true or nearly so from the start, having their own fluctuating variability, to be sure, but around a mean which does not approach that of the parental type in successive generations. Other variations behave quite differently. They may be selected generation after generation, modifying the stock up to a certain point, after which, if the variety is left to itself, there is revision towards the original parent. It is held by many that these two classes of variations are fundamentally distinct, and that only the first, so-called discontinuous variations, play an important rôle in the origination of new species. A considerable proportion of what is described as fluctuating variability is, in many cases, simply somatic variation, having no relation to the germ plasm. It is evident, however, that all fluctuating variability can not be such, otherwise species could not be modified by ordinary methods of continued selection. Our mathematical curves represent two kinds of variability lumped together and which it is in most cases practically impossible to separate. The character of height, for instance, in human beings is to a certain extent an inherited one, but it is determined to a marked degree by influences operating after birth. The usual curves of variation represent both and may even include also variations in the nature of mutations which fail of discrimination from the rest of the aggregate. De Vries distinguished three kinds of germinal variations, elementary species, retrograde varieties and fluctuations. These three kinds he conceives to be sharply distinguished and produced in different ways. All congenital variability is regarded by him as resting upon qualitative or quantitative changes in the pangens or the organic units of which he conceives living matter to be built up. The pangens form the basis of the unit characters, or independently variable elements of the organism, there being a special kind of pangen for each such character. Variations in the number of pangens cause variations of the fluctuating type which obey Quetelet's law of chance frequency distribution. De Vries maintains and attempts to prove by the citation of several examples that through the selection of such variations modification may be carried to a certain point, but soon a limit is reached beyond which selection is incompetent to effect further improvement. Moreover, continued selection must be practised in order to maintain the condition which has been reached, else the stock will in the course of a few generations revert more or less completely to the ancestral mean. Retrograde varieties, according to De Vries, are sharply distinguished from fluctuations. They are, as a rule, constant from the start, and differ from the type in only one or at most a very few respects. They originate for the greater part in a negative way by the apparent loss of some quality and rarely in a positive manner by acquiring a character seen in allied species." "By far the greatest part of the ordinary garden-varieties differ from their species by a single sharp character only. In derivative cases, three or even more such characters may be combined in one variety, for instance, a dwarfed variety of the larkspur may at the same time bear white flowers or even double white flowers, but the individuality of the single characters is not in the least obscured by such combinations. These varieties, says De Vries, "do not possess anything really new." The loss of a character is merely apparent. "On a closer inquiry we are led to the assumption of a latent or dormant state. The presumably lost characters have not absolutely, or at least not permanently disappeared. They show their presence by some slight indication of the quality they represent, or by occasional reversions. They are not wanting, but only latent." In other words, the only difference between retrograde varieties and the types is the latency or patency of certain characters. The same kinds of pangens are present in the germ plasm of both. Elementary species, on the other hand, are distinguished from their nearest allies in almost all organs. There is no prominent distinctive feature between the single forms of Draba verna, Helianthemum or of Taraxacum; all characters are almost equally concerned. The elementary species of Draba are characterized, as we have seen, by the forms and the hairiness of the leaves, the number and height of the flower stalks, the breadth and incision of the petals, the forms of the fruits, and so on. Every one of the two hundred forms included in this collective species has its own type, which it is impossible to express by a single term. Their names are chosen arbitrarily. Quite the contrary is the case with most of the varieties, for which one word ordinarily suffices to express the whole difference. The most important distinction which De Vries draws between retrograde varieties and elementary species is a physiological one. 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