Sketch of the Relationship Between American and Eastern Asian Fruits

SKETCH OF THE RELATIONSHIP BETWEEN AMERICAN AND EASTERN ASIAN FRUITS. By L. H. BAILEY, Jr., Professor of HorUculture, Cornell University^ Ithaca, N. Y, The fact must have struck every thoughtful horticulturist that Japan is now the most prolific source of profitable new types of fruits and hardy ornamental plants. The recent extension of communication with that country explains the introduction of these plants, but it does iiot account for the almost uniform success which attends their cultivation in this country. There must be some striking similarity between the climates and other conditions of Japan and America to enable plants from the very antipodes to thrive at once upon their introduction here. It is well known among naturalists that this similarity in climate exists, and that, therefore, there is general accord in the fauna and flora of Japan and eastern America. The origin of this resemblance was most strikingly explained by the late Asa Gray, professor of botany in Har- vard University, so long ago as 1859. But this relationship of Japan and America, with the practical deductions which follow an under- standing of it, has never been presented in its horticultural aspects. Before proceeding to a discussion of Gray's argumentative paper, it should be explained that half a century ago there was no satisfactory explanation of the means by which plants and animals have become widely disseminated over the earth. This was particularly true respect- ing the curious phenomena of disconnected distributions, or the fact that some species occur in widely separated and isolated places. Cer- tain plants occur only in eastern America and in Japan, and there may be no other representatives of the genus extant 5 that is, the genus is monotypic and has a peculiarly disjointed distribution. There are also certain bitypic genera, of which one species occurs only in eastern America and the other in Japan. There are equally strange distributions of plants and animals in other parts of the world. At the time Gray wrote, there were a few general hypotheses in vogue to account for these detached distributions. One was Agassiz's theory, which has been called the autochthonal hypothesis, from the fact that it sup- poses that each species was born or brought forth upon the area which it occupies (autoclithonj one born of the land itself). It ^^maintains, substantially," says Gray, ^'that each species originated where it now occurs, probably in as great a number of individuals occupying as large an area, and generally the same area, or the same discontinuous area, as at the present time." 437 438 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. Miicli tlie same view was held by Schouw, of Copenliagen, who advanced the hypothesis of the double or multiple origin of species; but he supposed that the species had the power of greatly distributing itself when it was once created in a given region. It Avas even then (Schouw wrote in 1837) maintained by various naturalists that species had sprung from one progenitor; but Schouw declared that ^^when we look at the facts presented by existing geographical distribution, this hypothesis becomes highly improbable, in certain cases altogether inad- missible.'- All the known agents of the distribution of animals and plants could not account for the fact " that many species of plants are common, on the one hand, to the Alps and the Pyrenees, on the other to the Scandinavian and Scotch mountains,^ without these species being found in the plains or on the lower mountains lying between; that the flora of Iceland is almost the same as that of the Scandinavian mountains; that Europe and îTorth America have many plants in common, particularly in the northern regions, which have not been transported by man; and still further dififtculties, bordering on impossibility, arise for such an explanation when we know that species occur in the Straits of Magellan and in the Falkland Isles which belong to the flora of the Arctic Pole." In order to account for these anomalous distributions, he supposed that the same species may originate several times, although it would appear that this multiple origination is waning, from the instances which he cites of the less wide and not detached distribution of the mammals and the higher plants, which are, presumably, of com- paratively late creation. <' Just as we have seen that the leafless and flowerless plants are oftener rediscovered in distant countries than those bearing flowers, we may assume that the more perfect animals are less prone to, perhaps never do, make their appearance in several places independently.'^ Schouw supposed that creation is completed. "I hold it in the highest degree probable,'' he writes, ^' if not strictly proved, that no new species originate at present." The straits to which naturalists were driven to explain the distribution of animals and plants when one progenitor is alone assumed may be illustrated by the supposition which Schouw ascribes to an English author, that there must have been a continental area between Spain and Ireland, inasmuch as certain Spanish plants reappear in the British Isles. Even Alphonse de CandoUe, while holding in general to the hypothesis of a. single origin, felt obliged to admit that in the case of our modest verbena-like FJiryma Leptostachya, which grows in eastern North America and again in the Himalayan region, there must have been two independent originations. îiaturalists were ready to believe that species had one origin, if only the fact of disconnected distributions could be explained. At this junc- ture Asa Gray came forward with his brilliant exposition of the rela- tionships of the eastern American and Japanese floras. The plants collected in Japan in 1853 by Williams and Morrow, in connection with AMEBICAN AND BASTEEN ASIAN FEÜITS. 439 Commodore Perry's visit to that country, and also those procured there by Charles Wright, in connection with Commodore Eodgers's expedition of 1855, went to Gray for study. He was at once struck by the similarity of many of the plants to those of our Alleghany region, a resemblance which he had before noticed. He found that many of the char- acteristic genera of eastern America and a number of the monotypic and bitypic genera occur also in the Japanese region. He observed the remarkable fact that the flora of eastern Korth America is much more like the Japanese flora than that of western America, or even of Europe, and also that our Alleghany flora is more like the Japanese than it is like the European. RESULTS OF CHANGE IN CLIMATE. It is well known that the climate of the Pliocene epoch, preceding the Glacial time, was much milder than now. Over the Dakotas, camels, horses, a mastodon, a rhinoceros, and an elephant roamed, and the temperate floras extended much farther north than they do at the present time. The same conditions prevailed in northern Asia, and the floras of the two continents were coterminous and intermingled. Then came on the Glacial epoch, "an extraordinary refrigeration of the north ern hemisphere, in the course of ages carrying glacial ice and arctic climate down nearly to the latitude of the Ohio. The change was evi- dently so gradual that it did not destroy the temperate flora. * * ♦ These [the plants] and their fellows, or such as survive, must have been pushed on to lower latitudes as the cold advanced, just aâ they now would be if the temperature were to be again lowered; and between them and the ice there was a band of subarctic and arctic vegetation, portions of which, retreating up the mountains as the climate amelio- rated and the ice receded, still scantily survive upon our highest Alle- ghanies, and more abundantly upon the colder summits of the mountains of JSTew York and î^ew England, demonstrating the existence of the present arctic-alpine vegetation during the Glacial era, and that the change of climate at its close was so gradual that it was not destructive to vegetable species.'^ So the plants were driven to the southward, both down the Asian and American continents. Gradually the ice melted away, the climate became milder, and plants began to return northward. After the Glacial epoch had passed away the arctic regions became warm. The great fluvial period came in, when arctic lands were lower than at present, when the sea stood 500 feet above its present level, and when the northern rivers were vastly larger than now. This great expanse of water and low elevation of land caused the warmer climate of the high north. Elephants and rhinoceroses roamed northward to the very shores of the Arctic Ocean, and lions, elks, horses, buffaloes, and mastodons inhabited the high latitudes. In the ice of Siberia the elephants are still found, even with their hair intact, pre- served in Nature's refeigerator for ages. There is evidence that north- 440 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. western America and nortlieasteriÄAsia were more closely connected by land than now. The Siberian elephant roamed from one continent to the other. '^I can not imagine a state of circumstances,'' writes Gray, "under which the Siberian elephant could migrate and temperate plants could not." So the floras of America and Asia again became coterminous. Now came another change. The Terrace epoch came slowly on. The arctic lands were elevated, the waters receded, and the temperature fell. The earth approached its present condition. The plants were again driven southward down Asia and America. The western coast of America, by reason of ocean currents, was warmer than the eastern region or than the Japanese region, and the temperate floras went down or persisted in similar climates, giving our Alleghany regions and eastern Asian and Himalayan countries similar floras.

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