Yearbook of Agriculture (1894) pp. 437-442
SKETCH OF THE RELATIONSHIP BETWEEN AMERICAN AND EASTERN ASIAN FRUITS.
L. H. BAILEY, Jr.
Professor of Horticulture, 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 not 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 Harvard University, so long ago as 1859. But this relationship of Japan and America, with the practical deductions which follow an understanding 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 respecting the curious phenomena of disconnected distributions, or the fact that some species occur ill widely separated and isolated places. Certain plants occur only in eastern America and in Japan, and there may be no other representatives of the genus extant; 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 tailed the autochthonal hypothesis, from the fact that it supposes that each species was born or brought forth upon the area which it occupies (autochthon, 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 time present time."
Much the same view was held by Schouw, of Copenhagen, 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 was even then (Schouw wrote in 1837) maintained by various naturalists that species had sprang 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 inadmissible." All the known agents of the distribution of animals and plants could not account for eredithe 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 North America have many plants in common, particularly in the northern regions, which have not been transported by man; and still further difficulties, bordering on impossibility, arise for such all 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 comparatively 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 Candolle, while holding in general to the hypothesis of a single origin, felt obliged to admit that in the case of our modest verbena-like Phryma Leptostachya, which grows in eastern North America and again in the Himalayan region, there must have been two independent originations.
Naturalists were ready to believe that species had one origin, if only the fact of disconnected distributions could be explained. At this juncture Asa Gray came forward with his brilliant exposition of the relationships of the eastern American and Japanese floras. The plants collected in Japan in 1853 by Williams and Morrow, in connection with Commodore Perry's visit to that country, and also those procured there by Charles Wright, in connection with Commodore Rodgers's expedition of 1855, went to Gray for study. 11e was at once struck by the similarity of many of the plants to those of our Alleghany region, a resemblance which be had before noticed. He found that many of the characteristic 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 North 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 foras extended much farther north than they do at the present time. The same conditions prevailed in northern Asia-, and the floras of time two continents were coterminous and intermingled. Then came on the Glacial epoch, "au extraordinary refrigeration of the northern hemisphere, in the course of ages carrying glacial ice and arctic climate down nearly to the latitude of the Ohio. The change was evidently 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 as 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 ameliorated and the ice receded, still scantily survive upon our highest Alleghanies, and more abundantly upon the colder summits of the mountains of New York and New 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 time elephants are still found, even with their hair intact, preserved in Nature's refrigerator for ages. There is evidence that northwestern America and northeastern Asia 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. Subsequently only minor distributions have taken place. The eastern Asian flora has shown some tendency to extend westward, and some species have reached Europe. Thus we have an explanation of the remarkable fact, long ago noticed by Bentham, that American species have reached Europe through Asia.
"Under the light which these geological considerations throw upon the question, I can not resist the conclusion," writes Gray, "that the extant vegetable kingdom has a long and eventful history, and that the explanation of apparent anomalies in the geographical distribution of species may be found in the various and prolonged climatic or other physical vicissitudes to which they have been subject in earlier times."
A certain flora "established itself in Greenland," says Sir J. W. Dawson, "and probably all around the Arctic Circle, in the warm period of the earliest Eocene, and, as the climate of the northern hemisphere became gradually reduced from that time till the end of the Pliocene, it marched on over both continents to the southward, chased behind by the modern arctic flora, and eventually by the frost and snow of the Glacial age." Says Dawson, again:
If, however, our modern flora is thus one that has returned from the south, this would account for its poverty in species as compared with those of the early Tertiary. Groups of plants descending from the north have been rich and varied. Returning from the south, they are like the shattered remains of a beaten army. * * * It is, indeed, not impossible that in the plans of the Creator the continuous summer sun of the arctic regions may have been made the means for the introduction, or at least for the rapid growth and multiplication, of new and more varied types of plants. * * * What we have learned respecting this wonderful history has served. strangely to change some of our preconceived ideas. We must now be prepared to admit that an Eden can be planted even in Spitzbergen; that there are possibilities in this old earth of ours which its present condition does not reveal to us; that the present state of the world is by no means the best possible in relation to climate and vegetation; that there have been and might he again conditions which could convert the ice-clad arctic regions into blooming paradises, and which at the same time would moderate the fervent heat of the tropics. We are accustomed to say that nothing is impossible with God; but how little have we known of the gigantic possibilities which lie hidden under some of the most common of his natural laws!
All these considerations go to establish three general laws: (1) That distribution of plants and animals is determined largely by climatic and other physical causes. (2) That species have a local or single origin. (3) That the origin of our present temperate flora is in the north. These generalizations were written before Darwin's theories appeared and before Heer had published the fossil histories of the arctic regions, and they at once establish Gray's place among philosophical naturalists.
We have now observed that the very facts which led Schouw, De Candolle, and others to accept an hypothesis of the multiple origin of species are the ones which chiefly explain and prove the conclusions of Gray. In the vicissitudes of geologic time plants retreated up the mountains or persisted along the cold shores of the northern lakes, giving rise to the curious fact of arctic and subarctic plants upon Lake Superior, Mount Marcy, Mount Washington, and Mount Katahdin. But, what is more to our present purpose, we can now understand the similarities of the eastern American and Asian floras, because like plants have persisted in similar climates when they were pushed down from the north upon all sides of the globe. The curiously dismembered diffusion of the Phryma Leptostachya is intelligible; and we can explain Schouw's perplexity concerning the less extended and undetached distribution of the mammals and higher plants, for these may, in many cases, have developed or originated since the epoch of these great dispersions.
The climates of eastern America and eastern Asia are still similar, as shown by the similar foras of the present time. The facies of the Japanese, northern Chinese, and Himalayan floras are strikingly those of our own Alleghany flora. The magnolias are peculiar to these two great regions. The tulip tree, confined to our Eastern States, has recently been discovered in China. The story of shortia and schizocodon—independeut names for the same type of plant discovered in the two continents—is familiar to botanists. Lately, horticulturists have seen a striking instance of this relationship in the remarkably rapid diffusion in this country of the Japanese plums, fruits which are more closely allied to our native species than the common or European plums are, and which are also unquestionably adapted to a much wider range of conditions than the European plums. We all know that the horticultural flora most resembling that of Europe is upon our Pacific Slope; there the European wine grape, the. olive, the citrous fruits, the walnut, the fig, and the prune and raisin industries are already well developed. In like manner we may expect that in the course of time the horticultural industries of eastern America and eastern Asia will acquire the similarity of facies which the floras of these regions now enjoy. One may therefore look with favor upon the introduction of Japanese plants, for it is certain, both from the known resemblances of its flora to our own and from the early introduction of its plants into western Asia and Europe, that the most promising field for horticultural exploration and for the study of the ancestry of our fruits is now in the interior of China.
FOREIGN CONTRIBUTIONS TO OUR POMOLOGY.
It is yet too soon to fully measure the value of the contributions of eastern Asia to our pomology, although the importance of the hardy ornamentals derived in great numbers from that region is everywhere conceded. Yet this antipodean region has already given us quite as important species of fruits as Europe and western Asia, despite the fact that these latter regions were the source of our colonization and civilization. The following list includes all the fruits of the United States which have come from the Europo-Asian region and from the Chino-Japanese region:
|Sour cherry||Chinese apricot|
|Quince||Kaki, or Japanese persimmon|
|Red currant||Lemon (including lime and citron)|
|Wine and raisin grape||Hovenia|
|European chestnut||Japanese chestnut|
|Twenty-two species||Twenty-one species|
|1 The raspberry and strawberry mostly supplanted by the American species.|
The eastern Asian species of fruits now grown in this country are already nearly equal in number to those from Europe and. western Asia—the latter country "the cradle of the human race"—and they comprise some of the most important fruits known to man, the orange, lemon, peach, apricot, and kaki. There is certainly abundant reason for looking toward oriental Asia for further acquisitions, either in other species or in novel varieties.