Page:Popular Science Monthly Volume 73.djvu/549

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man. The competition between allied species is thus often indirect, one destroying another by conveying to it some disease.

The flax is visited by various bees, which I have studied and recorded; these carry the pollen from flower to flower, and thus aid in pollination. Whether the necessary bees are always present, is not yet known; but their presence in numbers must be a favorable factor, and thus an important element in the living environment.

In the case of the snail, although it is so common, we know little or nothing about its natural enemies.

The more we study living creatures the more we become impressed by the complicated conditions necessary for the preservation of the higher forms, and the possibilities of local or complete extermination. As we determine these more accurately, we feel able to return to the fossils, and from them restore the past in much more detail than at first seemed possible. If a snail or a slug crossed from Asia to America we presume that it not only found continuous, or nearly continuous, land, but also that it did not traverse any desert. The path of migration of the blue flax was not, it is virtually certain, across a lowland region or swamp. Making all allowances for what are called accidental means of transportation, it ought to be possible to infer something about the pathway of a considerable number of species.

In all of these researches, success and failure are inextricably mixed, at least as regards the details. In no case can we gather all the pertinent facts; our knowledge of even the commonest species is very deficient. Yet, when all is taken together, we find ourselves like the man who said he lost on every job, but was able to make money because of the multitude of them. The number of known species, living and extinct, is enormous, and the data we have gathered, when suitably sorted and arrayed, will point to many definite conclusions. More especially is there reason to hope for good results to be derived from studies which past investigations have merely suggested and shown to be possible.

As a matter of history, as food for the imagination, it is interesting enough to watch and take part in the reconstruction of the past, especially when we are able to do this with a reasonable degree of completeness, as at Florissant in Colorado, or Ĺ’ningen in Germany. Much more, however, may come of these investigations. The problems of evolution, the intricate questions of heredity and variation, may be answered in part by such means as I have described.

The experimentalists, represented by Bateson, De Vries, Tower, MacDougal, Davenport and many others, have ascertained that what appear to be new species or races may arise suddenly by a process termed mutation. It even appears that in certain cases this process may be brought about by artificial means, such as differences of humid-