that neither of the series with which we are dealing is large enough to give very trustworthy results for the frequency of individual grades. We might avoid to some extent the difficulties introduced by the errors of random sampling by graduating the observed frequencies by some satisfactory fitting formula, but it does not seem profitable to take up the labor of curve fitting on the available data. We may, however, calculate the means and variabilities with their probable errors. The constants and

their differences appear in Table II.

The means show that the Wood's Holl plants have about three tenths of a seed more per pod than the Danby Dale series. This is to be expected from the diagram where the polygon for the American series is seen to lie a little further to the right than the English. But the difference is only about four times its probable error and so only doubtfully significant even for the samples in hand. I think no one can examine these results and not be convinced that so far as is shown by the physical constants

the two collections, one gathered in England and the other in America and counted and reduced by independent observers, are practically identical when we have regard to the probable errors of random sampling. And this notwithstanding the fact that the age of the plants, the number of plants involved, the ancestry of the individuals, and the climatic and soil conditions under which they grew are not taken into consideration or allowed for in any degree! If the constants were based on some character which the qualitative biologist would guess to be little influenced by the environment one might not be surprised at their close agreement; but we are dealing with

a character dependent not merely upon the internal and external factors determining the form of all plant organs, but upon the environmental factors influencing the chances for fertilization as well. Furthermore, it may be noted that we are dealing not with a little variable character, but with one having a coefficient of variation of about thirty five per cent. This is about two or more times the value of the coefficient of variation of the ordinary vegetative characters of plants, but not an extraordinarily high value for seed numbers, as determined from large series of unpublished data.

Summarizing the results of this note, I think we may say that so far as is shown by this one series of material Cytisus is no more variable in the habitat to which it has been very recently introduced than it is in one of its native habitats. As a matter of fact it is slightly, though not significantly, less variable at Wood's Holl than at Danby Dale. Possibly the sensible identity of the variability of the two samples may be due to the small number of individuals which furnished my series of data. These in their turn were probably derived from very few ancestors. I attach no great importance to the results. They simply show that so far as the present material is concerned there is no evidence in favor of the theory that the introduction of a species into a new habitat increases its variability. Possibly some other character than number of seeds per pod would have shown an increased variablity. I use this character merely because I had the data on hand as a by-product of some other work and felt that it would be better to let it contribute its bit of evidence on this problem than to throw it away. Possibly as a fellow biologist remarked when I showed him the closeness of agreement of the constants from the two series the result is "purely accidental." There are many possibilities of error in work of this kind. But until we have a large number of series of quantitative data it will be quite impossible to say whether or not there is anything of value in the theory of an increased variability of "introduced species."

PRESENT PROBLEMS IN PLANT ECOLOGY1

THE TREND OF ECOLOGICAL PHILOSOPHY

PROFESSOR HENRY C. COWLES

UNIVERSITY OF CHICAGO

THAT Schimper was a prophet as well as an ecologist of the first magnitude is well attested by this sentence from the preface to his plant geography:

The ecology of plant distribution will succeed in opening out new paths on condition only that it leans closely on experimental physiology; thus only will it be possible to sever the study of adaptations from the dilettantism which revels in them, and to free it from anthropomorphic trifling, which has threatened to bring it into complete discredit.

The close interdependence of physiology and ecology is being more and more recognized; this is made manifest by a survey of the titles presented to the botanical meetings year by year. Suggestive among this year's titles are: Bog toxins and their effect upon soils; experimentally induced root-regeneration in Parthenium; the relation of evaporation to the treelessness of prairies; are alpine plants exposed to increased evaporation? Titles such as these would have been quite impossible a few years ago through the failure of ecologists to recognize the fundamental necessity of building their work upon physiological foundations. Quite as fundamental but less fully recognized, especially by many physiologists, is the dependence of physiology upon ecology. The increasing sanity of physiological problems is due in large measure to the wholesome influence of ecology. In the old days when physiology was a mere laboratory science, and therefore artificial, no experimental test could be too

A series of papers presented before the Botanical Society of America at the Baltimore meeting, by invitation of the Council.

bizarre to be applied to plants. A thing never to be lost sight of is that evolution has taken place out of doors, and that the contortions of a puny plant in our illy lighted and gas-ridden laboratories do not solve our most important problems. In recent years no physiological work of greater import has appeared than that from the Desert Laboratory, where the direct stimulus to research has been contributed by the desert itself and its ecological problems.

The developments of the past decade, therefore, make it essential that physiology and ecology break down the barrier erected for them in Madison in 1893, where it was declared that physiology is experimental and ecology observational. The ecologist must experiment in order to resolve a natural complex of factors into its individual elements, while the physiologist must be a student of field conditions, if he wishes to deal sanely with the great problems connected with the evolution of form and behavior. Recognizing, then, the interdependence if not the complete identity of experimental ecology and field physiology, it becomes necessary to consider the underlying philosophy that serves as a motive for all research along these lines. The importance of one's philosophy upon his research can scarcely be overestimated, for it determines the problems to be attacked, the methods to be employed, and, on account of the personal equation, is likely to give some color to the results secured. But it is not necessary that the working theory be true; indeed it is often better that it be most untrue, since it may thus lead to the testing of more theories than might otherwise be employed. The fundamental test of a working theory is that it be that one which will stimulate the maximum of discriminative research. There can be given no better illustration of an unproductive theory than the theory of vitalism. This supposes that there is a fundamental difference between the living and the nonliving, hence one would not expect a vitalist to lead in the attempt to create living matter by experiment.

Vitalism, whether true or not, conduces to lethargy, because it assumes a barrier instead of attempting to find if the supposed barrier can be broken down. Thus the mechanistic theory of life is best as a working hypothesis because it leads to decisive experimentation and to the attempt to create living matter, and in this way leads to the solution of many great problems and may some day cause the settlement of that greatest of all problems, the origin of life. On the other hand, vitalism, by assuming to answer the question in a way that transcends the possibility of experimental test, is a hopeless theory and leads to repose and scientific slumber rather than to activity.

While theories of vitalism in whatever form have ever blighted scientific endeavor, they have been especially harmful in ecology. No biologists are brought into closer touch with life than are the ecologists; their whole atmosphere is pregnant with dynamics and the aspect which they have of plants is that of extreme plasticity. The ecologist comes into daily contact with profound changes in plant form and behavior, and he sees ever before him the panorama of succession. What wonder is it that many ecologists have been carried off their feet by vitalism and have dabbled in anthropomorphic similes? And what wonder that, because of this attitude, some of our best biologists have seen naught in ecology but superficial vaporings or scientific nonsense? But the view-point of ecology has been shifting, indeed has largely shifted, and there are reasons for believing that the ecologists are now closer to the problems of to-morrow than many of the other biologists. The rescue of ecology from dilettantism and anthropomorphic trifling, which Schimper so keenly wished for a decade ago, has been essentially realized. It may be of value to outline the steps that have led to the present happy state.

From the beginning one of the greatest of ecological problems has been that of the origin and significance of adaptations. In other days the solution was sought in special creation, one of the most unscientific of all