ant director of Mt. Wilson Solar Observatory, Pasadena, Calif., and G. STRÖMBERG. The spectroscopic method of deriving the absolute magnitudes of stars and a new formula connecting parallax and proper motion have been utilized to study the relationship between the motions of stars and their true or absolute magnitudes. About one thousand stars have been used in the investigation. The results establish almost certainly a definite increase of velocity with decrease in brightness. In radial velocity this is of the order of 1.5 kilometers for each magnitude for stars of the F, G, K and M types of spectrum. This is to be interpreted, probably in part at least, as an effect of mass: that is, the smaller stars move more rapidly than the larger stars. This increase of velocity with decrease in brightness is found to persist among the groups of stars arranged according to their distance from the sun. Accordingly the evidence does not indicate that the nearer stars are moving more rapidly than the distant stars. (In Nebula: V. M. SLIPHER, Ph.D., director of the The present status of knowledge about early man in America may be summed up as follows. Early man was here. He lived during at least a part of the Pleistocene period for tens of thousands of years south of the glacial moraines. He probably went through an Eolithic period and certainly through a Chelleen period in some places and therefore was truly a Paleolithic man. He may have made rudimentary fine art. Paleolithic American man was the ancestor of the Neolithic historic Indian and although less advanced in culture much like his descendant in anthropological characteristics. Whether he was an autochthone in America or whether he came from some other place and if so when, we do not as yet know positively, although his affiliations seem to be to the west. And it is to four men above all others that we owe our knowledge: Abbott, the discoverer of paleolithic implements and horizons; Volk, the corroborator; Lund, the first finder of probably Paleolithic bones, and Winchell, the investigator of patination. The influence of the admixture of present immigrant races upon the more original stock: CHARLES B. DAVENPORT, S.B., Ph.D., director, Station for Experiment Evolution, Cold Spring Harbor, Long Island. A new Babylonian account of the creation of man: APRIL 13 Albert A. Michelson, Ph.D., Sc.D., LL.D., F.R.S., Vice-president, in the Chair Crushing of crystals: PERCY W. BRIDGMAN, assistant professor of physics, Harvard University. Hollow cylinders cut from single crystals have been subjected to unique tests by applying large hydrostatic pressures to the external surface. The crushing strength under these conditions is much higher than that found by ordinary tests, and the manner of failure is different. This has an interesting geological significance in suggesting that open cavities may persist in the earth's crust at greater depths than could be expected from the usual methods of measurement. Structure of the spectra of the phosphorescent sulphides (describing measurements by Drs. H. E. Howe, H. L. Howes and Percy Hodge): EDWARD L. NICHOLS, Ph.D., D.Sc., LL.D., professor of physics, Cornell University. The Corbino effect in liquid mercury: EDWIN PLIMPTON ADAMS, Ph.D., professor of physics, Princeton University. Spontaneous generation of heat in recently hardened steel: CHARLES FRANCIS BRUSH, Ph.D., Sc.D., LL.D., Cleveland. I., Condensation and evaporation of metal films; II., The minimum potential for excitation of the "D" lines of sodium: ROBERT WILLIAMS WOOD, A.B., LL.D., professor of experimental physics, Johns Hopkins University. Growth and imbibition: D. T. MACDOUGAL, Ph.D., LL.D., director of department of botanical research, Carnegie Institution of Washington, and H. A. SPOEHR. The mechanism of overgrowth in plants: ERWIN F. SMITH, B.S., Sc.D., Bureau of Plant Industry, Department of Agriculture, Washington, D. C. The behavior of self-sterile plants: EDWARD M. EAST, Ph.D., professor of experimental plant morphology, Harvard University. There are really two problems connected with the inheritance of self-sterility in plants. One is the relation between self-sterile and self-fertile plants, the other is the behavior of self-sterile plants when crossed together. They should not be confused. The Nicotiana self-fertility is completely dominant over self-sterility. Either of the self-sterile species Nicotiana alata or Nicotiana forgetiana may be crossed with the self-fertile species Nicotiana langsdorffii. The result in each case is an F, generation that is completely selffertile. The F, plants show the usual monohybrid ratio of 3 self-fertile to 1 self-sterile. Given the basic factor for self-sterility in the homozygous condition as in the case in Nicotiana forgetiana and Nicotiana alata, two plants may be either cross-fertile or cross-sterile with each other. Reciprocal crosses always give the same result. Thus the character behaves as if it were sporophytic rather than gametic. In other words, the constitution of the mother plants and not the constitution of the gametes which they produce determines whether a combination shall be fertile or sterile. This fact indicates very strongly that gametes have no other function than fusion with their complements, that the potential characters which they carry are wholly latent until the development of the zygote begins. The cross-sterility shown is of such a nature that if plant A is sterile with plants B and C, plant B must be sterile with plant C. Generalizing upon the basis of the behavior of self-sterile plants in intercrosses one may say that a self-sterile population consists of a small number of groups of plants each plant being cross-sterile with all plants belonging to the same group and cross-fertile with all plants of all other groups. These facts naturally lead to the conclusions that the behavior of self-sterile plants in inter-crosses is regulated by several transmissible factors all of which are distinct from the single basic factor for self-sterility and which presumably may be carried by self-sterile plants. A plant homozygous for self-sterility can neither be fertilized by its own gametes nor by the gametes of any other self-sterile plant of like constitution as regards these regulation factors, but any two plants differing in these regulatory factors are cross-fertile. Twin hybrids from Enothera lamarckiana and franciscana when crossed with Enothera pycnocarpa: GEORGE F. ATKINSON, head of the department of botany, Cornell University. Enothera lamarckiana × E. pycnocarpa. There is a splitting in the F, with production of twin hybrids. One of the twins (pycnocarpa type) has rosette leaves narrow and deeply cut over the basal half as in E. pycnocarpa, but the leaves are The strongly crinkled as in E. lamarckiana. The other twin (lamarckiana type) has rosette leaves, narrow furrowed, not crinkled as in E. pycnocarpa, but with plain edge as in E. lamarckiana. The rosettes of the pycnocarpa type strongly resemble those of E. pycnocarpa because of narrowness and cutness, while at the same time they resemble E. lamarckiana in convexity and crinkledness. general appearance of the rosettes of the lamarckiana type suggests neither parent, since the factors selected represent the less striking character of each. These two twin types are fixed in the first generation, since they are repeated in the F, and probably in the following generations in accord with the usual behavior of twin hybrids determined by de Vries. The progeny is remarkably uniform, in that respect following the feature of uniformity in the progeny of the parents, except for an occasional mutant from the pycnocarpa type. This mutation factor is probably inherited from lamarckiana. Enothera franciscana × Œ. pycnocarpa. There is a splitting in the F, with production of twin hybrids. One of the twin hybrids (pycnocarpa type) has rosette leaves with the narrowness and cutness of E. pycnocarpa, but otherwise modified by E. franciscana. The other twin has rosettes very similar to those of Œ. franciscana, somewhat modified by E. pycnocarpa, and showing considerable fluctuating variations, parallel with those of E. franciscana. In the F, generation there is a one-sided splitting similar to that which occurs in the F2 of twins from E. hookeri . lamarckiana described by de Vries. The pycnocarpa type twin has a hybrid constitution and in the F, splits into two types, the pycnocarpa type and the franciscana type, the latter presenting fluctuating variations parallel with those in the parent franciscana. The other twin (franciscana type) is fixed in the F, since it repeats itself in the F, and probably in the succeeding generations, but it presents the fluctuating variations characteristic of the parent franciscana. The franciscana twin probably carries the pycnocarpa factors also, but in a subordinate or permanently latent condition. If so, it is a physiological homozygote. If it is possible to introduce a splitting factor into the franciscana twin by an appropriate cross, and cause the pycnocarpa character to reappear in some of the progeny, the fundamental heterozygotic constitution of the franciscana twin would be demonstrated. 2 ARTHUR W. GOODSPEED, Secretary (To be continued) SCIENCE PLANT ECOLOGY AND ITS RELATION TO AGRICULTURE1 I. CONTENT OF ECOLOGY A. Nature and Scope.-In beginning this discussion, a brief statement as to the nature and scope of ecology seems to be desirable on account of the hazy popular notions on the subject. Outside of a rather narrow circle one usually finds a total ignorance of the meaning of the word itself, and even among biologists, some are familiar only with the observational side, due probably to the early prominence of the "car-window" school of ecologists, while others consider that the subject-matter of ecology might better be divided between morphology and physiology, and frankly state their opinion that there is no such subject as ecology. However, there seems to be a mass of subject-matter belonging to neither department exclusively, but partly to each, which would fairly warrant the formation of another department. This has been named ecology, and may be defined as the science of organisms as affected by the factors of their environment. The connection with physiology is the closer of the two, and in fact, the two subjects overlap to a certain. extent, but whether we call this overlapping segment ecological physiology or physiological ecology, the character of its subjectmatter is sufficiently different to warrant a separate category and different treatment. The methods of ecology have been, of course, largely descriptive, but they are also becoming increasingly quantitative, employing in many cases elaborate and deli 1 Delivered before the Illinois Academy of Science, February 23, 1917. cate instruments. both in the field and in the laboratory, and under experimentally controlled conditions, as well as under natural. The great task of ecology and the purpose of its observation and experimentation lies in the interpretation of the phenomena and the deduction from these data of the general principles underlying the reaction of plants to their environmental factors. The work is pursued B. Content of General Ecology. 1. Autecology. This branch of ecology studies the plant as an individual, and is largely physiological in nature. It considers the general results of the relation of the plant to its environmental factors, as shown in the division of plants into great classes according to their reaction to each of the leading factors. These reactions come under three heads: First, the reactions in the activity only of the plant, as the increase of activity under favorable conditions and its diminution and even stoppage under adverse conditions. This group really belongs under the head of physiology, but when considered in the field under natural conditions it may be regarded as within the scope of ecology. Second, the effects on plastic tissues or organs of the plant. These may also be produced experimentally and frequently have an important bearing on the economic value of cultures. Third, the effects on permanent structure and function of plant organs. Whatever may be our belief as to the method by which variations are produced and fixed in plants, it is evident that structures correspond more or less to function and are conditioned directly or indirectly by the environment. A comparative study of plants in different habitats leads us to identify or construct from the imagination certain "normal" or original types of organs. We find also modifications of these types, which are either temporary, where the plant tissues are plastic; or permanent, constituting variations. In tracing the correspondence of these changes to environmental differences we look for and frequently think we find what may be called ecological causes. Plants are classified according to these modifications, both plastic and permanent, on the basis of the factor which seems to be chiefly responsible for the change. Chief among these is the moisture relation, expressed in the more or less familiar division into hydrophytes or water lovers, xerophytes or dry-climate plants, and mesophytes inhabiting an intermediate habitat. A similar relation to light and temperature divides plants into sun-tolerant and shadetolerant, heat-tolerant and cold-tolerant, groups. The relation to the chemical elements in the soil is not so marked as was once thought to be the case, yet we still hear such words as "calciphiles" and "calciphobes," and the terms probably represent to a certain extent a real situation. The best illustration of this is shown in a comparison of organs, especially leaves, of hydrophytic as compared with xerophytic and mesophytic plants. Here there seems to be a very distinct correspondence between structure and the markedly different environments of these different habitats. 2. Synecology, which studies plants in the mass, is largely concerned with distribution of plants, and may be regarded as an application of autecology in the grouping of plants within greater or smaller areas of the earth's surface. It may be divided into vided into (a) "Phytogeography," in which the groupings are regional and the result of climatic factors, and (b) "Physiographic Ecology," in which the groupings are local, as the result of physiography with attendant climatic modifications. These groupings are called plant associations and the fact that different associations follow each other successively is expressed in the term "Plant Succession." C. Special Ecology of Structural Groups. -While all ecological groups have more or less specific reactions which are considered under their appropriate heads, there is one grouping which demands separate treatment because it is based on the most striking structural feature-the presence or absence of woody tissue, and also because of its practical relation to man's activities. Although verging more closely on agriculture, it may still be classed as ecology because the point of approach is from the side of the environmental relations. On the basis of woody structure we classify plants basis of woody structure we classify plants as trees and herbaceous plants with shrubs and lianas occupying an intermediate position, and it is at once evident that these two groups have decidedly different ecolog ical reactions. 1. Ecology of Trees and Shrubs. This study would involve (a) description of leading species with their habits of growth, characteristic structures, and ecological interpretation of the same. This would be the autecology of the group. (b) The synecology would involve the distribution and range of the leading species and their relation to ecological causes. (c) We might notice also the influence of the species on their environment as illustrated in the influence of forests on soil moisture content through their control of run-off; and the influence of individual trees, as for example, the eucalyptus in the reduction of soil water; also the influence of forests on soil in the formation of humus and the effect of trees on wind, as in protection by windbreaks. (d) It could include also a classification of trees according to the character of their wood, including distribution of the different woods and methods of utilizing. Also a similar classification according to the character of their fruits, their chemical products and their value for ornament. 2. Ecology of Herbs.-Here should be studied (a) the general characteristics of herbs as distinguishing them from trees, with the ecological differences involved, under the heads of shoot, root, flower and fruit, with the characteristic differences between perennials and annuals; (b) a study of herbs as classified according to their value to man, as: valueless or "wild," those of economic value or "cultivated," and those undesirable or injurious, which we call "weeds." Uncultivated herbs are of interest chiefly synecologically as the associates of trees in their different groupings and as indicators of the characteristics of the environment, as hydrophytic, xerophytic, etc. As the subject of taxonomy has to do chiefly with the wild herbs it is frequently included under ecology to-day. Cultivated herbs and their attendant, though undesirable forms, are considered more from the autecological side. Their reactions to and tolerance of extremes of temperature and moisture and chemical conditions, are of course of chief importance. Original habitat and distribution and to some extent taxonomic relations, are also important as indicating suitability for certain environments. This value is testified to by the systematic search for new varieties carried on by the United States Department of Agriculture. Herbs vary greatly in their reactions to environmental factors, and should be grouped as far as possible along the lines of similar behavior. Knowledge of these groups should be as complete as possible, but a thorough study of the ecological reactions of a few type genera and species should be included in any comprehensive course in ecology. 3. The ecology of lower types of plants is not treated separately, but on account of |