His mind was of the penetrating order which worked persistently at any problem until he began to see light on it.

He was not concerned with practical aims; he was an idealist who desired knowledge for its own sake, and not for any utilitarian end; a naturalist who worked for pleasure in the work itself, and rejoiced in the advancement of science his work brought about.

He was not lacking in ambition, but it was ambition on a large scale, not to gain fame and position, but to create works which should seem to him worthy. Fame came unsought, and, as he tells us, it was a satisfaction to him to feel that he was held in esteem by those whom he himself esteemed.

He has sometimes been called an amateur, and in a certain sense this is true, in as far as he worked in several different scientific provinces, each of which requires a man's whole strength. But he had full command over these different provinces, at least as far as was necessary for the end he had in view. He was certainly not a restricted specialist. The zoologists accepted him as a zoologist, the botanists as a botanist, perhaps also the geologists as a geologist. But he was not an expert in any, or rather, it would be more correct to say, he was so wherever he himself had done productive work. For he was essentially self-taught, and had passed through no normal school of zoology or botany, but with his great energy and unflagging industry he had acquired a profound knowledge from books and from personal intercourse with specialists, and every piece of work he did added to this store of knowledge. He was perhaps the last not merely to survey, but to do productive work in every domain of biological science. Yet I will not assert this, for we have all been convinced in recent times through the evolution theory that it is not enough to be at home in a single science; it is necessary also to have at least a general acquaintance with the essentials of allied branches.

Darwin has sometimes been accused of being one-sided, of caring for nothing but his science. But this was not the case; it is less true of him than of many specialists in natural science. He had a wide knowledge of English literature, Milton and Shakespeare having been his favorite reading in his youth. In later life he had novels, historical works, and books of travel read aloud to him every day. He was fond of music, too, though, as we have said, he had no musical ear.

Darwin was a man not only of lofty, noble spirit, but of the tenderest feeling. Let anyone who doubts this read the touching pages in memory of his little daughter Annie, who died young; they form one of the most beautiful memorials ever dedicated by a father to his child. His son's picture of him, too, reveals the beautiful and intimate relations that prevailed between them, and the whole

quiet and joyous life of the Darwin family testifies to the cheerful and affectionate disposition of its head.

It remains to estimate the influence of Darwin's theories on his time and on the future. But this is a task for which a whole book would not be too much, and a task, moreover, which could be better accomplished on the two hundredth than on the one hundredth anniversary of his birth.

We can at least say, however, that the influence was a great and many-sided one, and that it will endure throughout all time. All who know the position of science before 1859 will be ready to admit this; the younger generation have grown up so thoroughly under the influence of Darwin's ideas that it must be difficult for them to realize the state of matters before his day.

Let us speak of biology first. But was there a biology then? Strictly speaking, there was not; there was a zoology, botany, and even anthropology. Each of these sciences consisted of a very large and well-arranged mass of facts, but with no intrinsic coherence among them. This was supplied by the theory of evolution. The different departments of science were not even then regarded as complete; it was well known that there were many gaps in our knowledge, but we were only seeking for missing details, whereas in reality it was the main thing that was lacking the unifying idea which Goethe had sought for, and tried to supply in his theories of the plant prototype, and of the skull.

The science of embryology, or, as we now call it, ontogenesis, at that time consisted of a great number of observations, interesting enough, but without any recognized unity; it was not a harmonious structure, but a collection of finely-cut building stones. But what a change when the luminous idea of evolution was added! Life seemed to be infused into the stones, and almost spontaneously they formed a magic edifice. The ovum, now at last recognized as a cell, was seen to be a reminiscence of the descent of all higher animals from unicellular organisms; rudimentary organs, such as the rudimentary eyes of blind cave animals, were found to be signposts indicating the racial history of these animals, and pointing back to their sight-endowed ancestors. This evolutionary view illuminated the whole science, and not embryology alone, but also "comparative anatomy," the understanding of the structure of animals. It became plain why the New Zealand kiwi should have little rudimentary wings under its skin, although it does not fly. It is not in order that it may conform to an ideal of a bird, as was previously thought, but because its ancestors had possessed wings which were used in flight.

Physiology also gained much, especially the theory of reproduction, of heredity, of organs, of the cell, and especially of the cell

nucleus. I do not mean to say that all these were the direct result of the idea of evolution, but they have an indirect connection with it. Anthropology gained quite a new interest after it was recognized that man, too, was a product of evolution. A vast number of problems presented themselves; it was necessary to investigate the gradual becoming not only of the body but of the mind, the evolution of the Psyche and all that flows from it. Before that time there had been a history of language, of law, of religion, of art, and so on, but it now became necessary to carry these further back-beyond Adam and Eve to the animal ancestors. Undoubtedly a study of the psychology of animals is one of the essential tasks of the future! I can here only give a few hints without elaborating them, but I must emphasize the fact that the idea of evolution, in the form in which Darwin presented it to us, has given an impulse to new life and further development in every department of human knowledge and thought; everywhere it acts as the yeast in cider-it sets up fermentation. This has already borne rich fruit, and we may hope for much more in the future.

Our greatest gain from the theory of evolution has, however, been the evidence it affords of the unity of nature, the knowledge that the organic world must be referred back to the same great everlasting laws which govern the inorganic world and determine its course. Even if formal proof of this be still wanting, the probability is now so strong that we can no longer doubt it.

It is not only the theory of evolution as a whole, but the active principle in it, the principle of selection, that is transforming and illuminating all our old conceptions. It is teaching us to understand the struggle, silent or clamant, among human races, their rivalry for the possession of the earth, and to understand, too, the composition of human society, the unconsicious division of labor among the members, and the formation of associations. The development of "classes" and their union in a State appears in a new light when looked at from this point of view. In this department a good deal has been already accomplished.

The study of human health must be particularly influenced by the theory of evolution, and a beginning has already been made in this department also.

But there is another and very important point in regard to which the theory of selection must be our guide. If we take a survey of the evolution of the world of life as we know it, we see that, on the whole, it has been an ascending evolution, beginning with the lowest organisms and advancing through higher and higher to the highest of all, man himself. It must be admitted that at certain stages in this evolutionary series we find retrograde steps (as, for instance,

parasites and sedentary animals), but on the whole the direction of evolution has been an ascending one.

I see no ground for assuming that this will be otherwise in the future. According to the principle of selection the best will survive in the future as in the past, and mankind will ascend. I do not believe we are likely to undergo any essential changes in a crude physical sense; we are not likely to grow wings, and even our mental powers may not be capable of much further improvement, but ethical improvement seems to me not only possible but probable, on the principle of selection. Mankind will never consist of wholly selfless saints, but the number of those who act in accordance with the ideals of a purer, higher humanity, in whom the care for others and for the whole will limit care for self, will, it is my belief, increase with time, and lead to higher religions, higher ethical conceptions, as it has already done within the period of human existence known to us. But here again I can only indicate without following out my ideas. I wished to express them, because the principle of selection has so often been applied in an inverted sense, as if the brutal and animal must ultimately gain the ascendency in man. The contrary seems to me to be true, for it is the mind, not the body, that is decisive in the selection of the human race.

Thus we see the principle of evolution intervening, transforming, re-creating in every department of human life, and thought, and endeavor. We owe this principle, which has been so fruitful in results, mainly to Charles Darwin, though he was not the only one nor the first to think it out. But it was he, with Wallace, who secured it its place in science and made it a common possession of mankind by working it out in all directions, and supporting it with another principle, that of selection, which explains the riddle of the automatic origin of what is suited to its purpose in nature. Thus he cleared away the obstacle which would otherwise have stood in the way of the acceptance of the theory of evolution.

By all this he has earned enduring fame in the annals of science. His own country has not been ungrateful to him. A colossal statue of him in marble decorates the British Museum; from the background of the entrance hall he looks down on the passers-by with the calmness of the sage. His mortal remains lie in Westminster Abbey beside those of Newton.

Fate, too, was kind to him. He could truly say that his life was a happy one, for it was filled with a great idea, and he was supported by the consciousness that Goethe expresses through his Faust: "Es kann die Spur von meinen Erdentagen nicht in Aeonen untergehen." This is true of Darwin, and we may think of him as one of the great immortals among men.

PRESENT PROBLEMS IN PLANT ECOLOGY: PROBLEMS

a

OF LOCAL DISTRIBUTION IN ARID REGIONS."

By Prof. VOLNEY M. SPALDING,

Desert Botanical Laboratory.

The physical conditions prevailing in arid regions are such as render it unsafe to admit without further investigation generalizations regarding their plant life which have been drawn from studies conducted elsewhere. This is sufficient justification of an attempt to analyze certain problems which confront the student of desert ecology in his efforts to apply knowledge or principles drawn from previous experience. These problems have the advantage of a certain clearness of definition, which corresponds in a way with the sharp features of the desert and its characteristic vegetation. Their solution may involve great difficulties, and some of them, with our present methods, may be incapable of solution, but they are, at all events, capable of clear statement.

In the attempt to present such a statement, which may or may not prove successful, I shall for the present limit the discussion to the desert country of the southwestern United States, for the sufficient reason that my own studies have been conducted in that region; and I shall omit all consideration of the higher elevations of the mountains, which, though in the desert, are not of it; so that whatever is said at this time will be understood to apply to the floor of the desert, that is, the great plateaus and valleys which from Texas to California lie between the mountain peaks and ranges, together with the long slopes and low hills which border them on every hand and form the natural approach to the mountains.

Proceeding in a manner that will be indirectly a record of personal experience, one of the first questions presented to a student of desert botany is this: What are the conditions that determine the successful occupation of a desert habitat by certain plants, but prevent its occupation by others?

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

Reprinted by permission from The American Naturalist, vol. 43, No. 512, August, 1909.