Popular Science Monthly/Volume 82/March 1913/A Chronicle of the Tribe of Corn
|A CHRONICLE OF THE TRIBE OF CORN|
ALEXANDRE DUMAS maintained that he weaved more history into his romances than the contemporary chroniclers did into their histories. Perhaps he did. At least the reader may lose himself in the marvelously interesting fancies of the great Frenchman, and if he gleans some points of fact they are gratuitous—features for which he has not paid. But when he finds that his cherished enmity toward Aaron Burr is founded on the fictions of political opponents, that the reformation was largely politics and not ethics, he feels in much the frame of mind as when in earlier days he was robbed of his belief in Saint Nicolas.
These statements are not intended as a libel on the political historian. They serve only to defend the title of this article. The modern historian depends, first upon the records of writers contemporary with the epoch under consideration, second, upon the corroboration or refutation of these records by circumstantial evidence. The biological historian uses precisely the same method. His contemporary records are the records set down by the plants or animals themselves—autobiographies, as it were. He has this advantage over the transcriber of written records, however, the plant autobiographies are true. There is no boasting, no glossing of faults, no exaggeration. The transcriber may misinterpret the record, but this is not the fault of the record. He has but to read it aright. The written record, on the other hand, may be false at the outset.
The story of the birth and evolution of maize, the plant at the basis of our national prosperity, is of interest not only to agriculturists and botanists but to historians and philosophers, for it is one of the crops whose cultivation is linked with the beginnings of civilization. It has taken some years to fit the puzzle together, but now the gaps are but few. Of course the proofs are not absolute. No proof is. But it may be left to the judgment of the reader whether the case is beyond the reasonable doubt of the lawyer. At least, it is typical of the reasoning
|Fig. 1. A Typical Maize Plant as described by the Botanists. (After Bonafous.)||Fig. 2. A Reproduction of the Chinese Drawing upon which Rested the Argument for Asiatic Origin of Maize. (After Bonafous.)|
of the botanical historian and has been carried further than that of any other plant that has been cultivated since before recorded time and of which the wild prototype is unknown.
The clues upon which the botanical detective works are many, and it is only by dovetailing numerous facts that the probability of a correct conclusion is increased until it is beyond question. That criminal detectives can establish a reasonable proof by circumstantial evidence was shown long ago by Poe. Mathematics does not recognize a series of coincidences. Coincidences do occur but not in series. If a series of facts point to the same conclusion, the probability that that conclusion is correct increases by multiplication, not by addition. If the probability that one throws heads with a coin is one half, the probability that he throws a pair of heads with two coins is one half times one half, or one quarter, not one half plus one half which would be a certainty. Thus the fictitious reasoners of Poe and Doyle have argued that if a series of independent circumstances point in a single direction, that direction is the proper one. If certain facts seem to be outstanding, they must be looked to, for their fallacies will sooner or later come to light. The same is true in botanical history as the following incident shows:
The sagas of Iceland show unquestionably that some time about the year 1000 the Norsemen landed in North America. Where they landed has been a question. The sagas describe the natives they met, the Skrellings, as small and ugly, great of eye and broad of cheek. "And they came in skin canoes." The description fits only the Esquimaux. The sagas relate further, however, that the Norsemen found mösurr wood and self-sown wheat and that in the spring they filled their boats with "wine berries." Students of the sagas have taken the wineberries to be grapes, the self-sown wheat to be wild rice and the mösurr wood to be maple. There were discrepancies here. The ethnologists say the Esquimaux have not wandered south, and the botanists find that the grape and the wild-rice do not grow in the northeast. It may also be pointed out that grapes are not gathered in the spring even in the most flourishing circumstances.
Some have ridiculed the sagas, some have brought the Esquimaux as far south as Boston, others have turned the Skrellings into Indians in spite of their description. It remained for a botanist, Professor M. L. Fernald, to show that the mösurr wood is birch, that the wild wheat is the Strand wheat (Elymus arenarius) a plant familiar to the Icelanders, and that the wineberry is either the mountain cranberry that is in its prime in the spring or one of the wild currants, both plants being known to the Norsemen as vínber or wine berries. The plentiful occurrence of these species north of the St. Lawrence River straightens out all the inconsistencies and makes the geography, ethnology and biology of the old sagas perfectly plausible.
This short illustration typifies the method of the botanical historian, though perhaps the details of his work had best be explained. Foremost in the significance of its evidence is the geographical distribution of the wild plant and its subvarieties. From this knowledge one may sometimes locate the point of origin with surprising definiteness. But often an important cultivated species has no known progenitor in the wild. This lack of information is unfortunate for the investigator, but not prohibitive of results. It makes the problem only that much more interesting. The next point of attack is to discover the distribution of the wild species nearest related by their structure and characteristics to the material under investigation. The fact that an organic evolution has occurred is the master key that unlocks many problems. Classification along natural lines was made possible by establishing the fact of evolution. The relatives of plants are hall-marked in a manner not often mistakable, and if the general family group is not too widely distributed, the problem may be considered as fairly well along.
If there are no near relatives extant, if the plant is the last leaf upon the family tree, one must turn to the evidence of the plant itself. By this I mean he must study the inheritance of the various characters
by which its varieties are differentiated and endeavor to find out how the features peculiar to it have originated. He may then be able logically to connect it with very distant relatives.
Now to turn to the collateral evidence. Collateral evidence on distribution and relationship is furnished by paleontology. Such data are really direct and important when fossil remains occur in sufficient quantities, but this is not often the case. It is usually fragmentary and can be classed with that of archeology. Neither archeology nor history furnishes certain proof of plant origin, however, as we shall see. Their evidence must simply be given the weight it deserves when considered with other facts. Lastly, philology furnishes indications as to the history of a species, for common names of cultivated plants are well preserved in the languages of the people who have used them. But, like other evidence, it must be accepted with caution. The cashew is called by the French pomme de Mahogani, which is all right except that it is not an apple and has nothing to do with mahogany. This shows how much worse a compound name is than a simple name, since with a simple name there can be but one error.
We shall endeavor to construct our history and evolution of maize along these lines, though not keeping the same order.
Maize has not been found in the wild state, although it is such a remarkable plant it seems improbable that with our present knowledge of plant distribution it should remain undiscovered if in existence. This fact has made the problem of its nativity very difficult, even though Americans have been satisfied of its new-world origin for some time. Competent critics have skillfully argued old-world origin, and from the strictly historical point of view there was earlier much to be said in their favor. The word maize (mays) itself is strictly American, but this name has been in use only since adopted by Matthiole in 1570. In modern European languages the common name has been one purporting to show eastern origin, in English Indian corn, in French blé de Turquie or Turkish wheat. Since maize is not wheat, it might almost be concluded it was not Turkish. The trouble was. one could not prove it. As a matter of fact, such names only show the tendency of a people simply to indicate the foreign origin of an introduced article, as when the French gave the name coq d'Inde or Indian cock to the American turkey. According to De Candolle maize was called Roman corn in Lorraine and Vosges, Sicilian corn in Tuscany, Indian corn in Sicily and Spanish corn in the Pyrenées. The Turks call it Egyptian corn and the Egyptians, Syrian dourra, which prove it to be neither Egyptian nor Syrian.
It has been generally agreed by historians that there was no Hebrew or Sanskrit word for maize and that there was no Egyptian representation of the plant. It is true, Rifaud found an ear of maize in a tomb at Thebes, but this was the work of a modern impostor, for if maize had been a crop of ancient Egypt, pictures of it would have been as plentiful as they are of other Egyptian plants. The plant certainly was not known in Europe in early times, but the question ever arose whether or not it could have been introduced from the East during the Middle Ages. Bonafous, who was the foremost writer on the subject in the early nineteenth century, took this view and was responsible for long continued doubt on the subject. The principal evidence on the question was that obtained from a charter drawn up between two crusaders in 1204, according to which seeds thought to be maize and brought from Anatolia were presented to the town of Incisa. Historians of the crusades made much of this charter, although botanists thought from
their description that the seeds might be sorghum instead of maize. The absurdity of relying on such isolated clues came out with the discovery that the whole charter of Incisa was a modern fabrication.
The only other evidence of eastern origin that there has been any trouble in demolishing is a picture of an ear of maize together with its ideograph in a Chinese book written some time between 1578 and 1597. Since the Portugese came to China in 1516 and to Java 20 years earlier, it is plain this is not good evidence of Chinese origin. During the half century between this date and the date of the article, nothing could be more probable than Portugese introduction of maize into China. Furthermore, the fullness of early Chinese records is such that they would hardly have remained silent on an important agricultural crop until 1578.
This dearth of early records of the plant in the old world shows convincingly the American origin of the plant, for after the discovery of America its cultivation became rapidly diffused, a proof that if indigenous to Asia it would have been important agriculturally for centuries.
On the other hand, no one has ever questioned the fact that maize was widely cultivated in America at the time the country was discovered by Europeans. It was the staple crop in both continents and had names in all the native languages. Its antiquity and importance are evidenced by its prominence in the religious rites of the people. The North American burial mounds, the tombs of the Incas and the temples of Mexico were made depositories of the seeds just as the tombs and temples of Egypt treasured wheat and barley. These facts do not indicate antiquity in cultivation equal to that of Egypt, however, for the
civilization of the Peruvians and Mexicans is known to be of a much later era. At the same time, one may assume a history much longer than that indicated by these data for two reasons: from its wide distribution and numerous ancient varieties, and from Darwin's discovery of its seeds mixed with shells buried in soil along the Peruvian shore that had become raised by natural action 85 feet above sea level.
The American origin of maize being assured, interest in our problem narrows. The Americas are large. To what particular part was the plant indigenous? First let me say that it is a peculiar fact that the vast territory now known as the United States produced no cultivated plants of first importance. Excluding the Jerusalem artichoke, some comparatively unimportant berries and some relatives of the apple, our country gave man no agricultural treasures. It merely accepted with thanks the lavish generosity of the tropics. As far as maize is concerned, the physiology of the plant itself corroborates this statement. It germinates and grows best in hot climates. We must look for the home of maize, therefore, in the plains or plateaus of tropical North
or South America—the plains because annuals do not develop in forested regions. Under the circumstances, our search need only be the less troublesome absentia search in botanical records, since the regions have been combed by botanical explorers for three hundred years. The result as far as maize is concerned was nil. Perhaps though the word nothing is too exclusive. First cousins of our interesting family were discovered in Mexico and Guatemala, the plant called teosinte; and experimental evidence indicates a sufficiently near relation to justify these regions as the original home of the emigrant. This evidence, which gives us a picture of the original plant, is now to be considered.
Maize varieties differing slightly from each other are now numbered by the hundred. Of these, five or six differ by very distinct characters and have come to be thought of as subspecies. Those known as dent, flint, pop, sweet and flour corns are familiar to every one. One known as Curagua with toothed leaf edges, one with very hairy leaves known as hirta and one in which each seed is covered with husks or glumes known as tunicata are not so common. These varieties are our heritage from the aboriginal inhabitants, for each was known and cultivated somewhere
on the continent before the arrival of Europeans. They are considered by botanists as one species. The wild relative teosinte has been thought to be not only a distinct species but a member of a different genus. There is good evidence, however, that there is not a much greater difference between teosinte and the maize nearest like it than there is between a number of the most distinct maize varieties. These facts make it reasonable to suppose that both types arose from a common ancestor slightly different from each.
Teosinte and maize belong to the tribe Maydeæ, a division of the Gramineæ or true grasses. Our final problem is to connect the steps in the evolution of maize that distinguish it from the more typical grasses and if possible to picture the restored original form. The data from which one can do this come from observations of thousands of crosses between the different maize varieties.
Sweet corn is probably the most recent type. Sweet corns are simply dent, flint, pop and floury types that have lost the ability to mature starch grains. This is proved by crossing it with starchy kinds. For example, dent corns crossed with certain sweet corns produce flint types in the second hybrid generation. Starchiness is put into the hybrid by the dent variety and the latent flintiness of the sweet variety appears.
In the same way crossing indicates that as the pop or poplike varieties increased in size by numerous slight variations, the flint, the dent, and the floury kinds were produced through the correlation between the structure of the seeds and their size. This brings us back to a many-branched pop-like variety, examples of which are common enough to-day.
Most maize varieties have naked seeds, a feature unlike other grasses including teosinte. The remaining members of the family have
the seeds protected from animal marauders by husks or glumes. This is again a simplification caused by the loss of a character, as is proved by crossing the ordinary maize varieties with the variety tunicata in which the character still remains. This gives us a grass-like corn with each seed covered—a plant in many ways like teosinte. It still differs from it by but one important and several unimportant characters, and the difference can not be particularly significant, for maize and teosinte cross freely and give fertile hybrids.
The difference is this: The female or pistillate spike of maize, the part which we call the ear, consists apparently of several two-rowed
spikelets grown together; the same part in teosinte consists of bundles of distinct two-rowed spikelets with jointed axes. It takes two steps to bring maize to something like this condition. Ordinary maize varieties often produce individuals that have ears branched in much the same manner as the tassel or male spike. This is probably a reversion toward a former type. At least, pure varieties of this kind can be isolated. Furthermore it can be shown by crossing that the branched condition is due to a single hereditary character that has been lost by the cultivated kinds. The other step is the increase in number of rows, giving us the fine ears with from 18 to 24 rows that take the prizes in the agricultural shows. This feature is probably not due to the growing together of the spikelets. It is much more likely that increased number of parts came about through progressive variations, much as the increase of petals has brought the horticulturist so many double flowers. This type of variation is very common and still continues in maize, for the prize ears of the exhibitions contain many more rows than the more ancient little flints that were grown by the east coast red men.
The fact that but two essential variations, kinds that continue to occur, separate teosinte from the maize nearest like it, combined with the fact that the two are fertile in crosses lead me to believe that the two plants are simply diverse types of the same polymorphic aggregation, although they may be called species if one desires.
Perhaps we should stop here and not follow the path of speculation to its uttermost limit; still there are two more backward steps indicated by studying the cultivated plant. The plant is monœcious; that is, the male organs and the female organs are borne in separate flowers, though both are found on the same plant. This condition is not uncommon among the grasses although it is not the primitive condition. The unique fact is that the female flowers that form the ears are borne on short branches in the axils of the leaves of the maize stalk, while the male flowers are borne in a terminal spike, the tassel. This method of flowering is not so peculiar if the ear branch is examined. The husks that surround the ear are merely the leaves of the lateral branch upon which the ear is borne as a terminal spike. The lateral branch has simply shortened. It is telescoped together until the distance between the nodes is sometimes not more than an eighth of an inch. It seems just to conclude from the number of these internodes that the ear branch was at one time as long as that portion of the main stalk above the ear, that the flower spikes of the ancestral plant were once more or less level topped, bringing them into a horizontal plane. What caused the change we do not know, but if the plants were already monœcious before the change, and such a variation occurred, it would have been likely to have continued to exist in competition with the parent form on account of the greater chance for perfect fertilization of the silks.
The last step in our history is to make ancestral maize a perfect flowered species; that is, a form in which each flower has both male and female organs. There is no question but that this was once the case. "We know it by the characters possessed by the more ancient wild grasses and by the ease with which the plant reverts to the former condition. No one has isolated a race that breeds true to the older type, but every one who has raised corn has seen hundreds of tassels containing little seeds. It would seem that kindly external conditions alone are sufficient to bring back to the corn the memory of its old habit. When moisture is plentiful and the soil fertile, one can see these freaks by the hundreds in almost every field. The production of male flowers or their essential parts, the stamens, on the ears is much more rare, but it does occur.
Onr history is complete. We can picture to ourselves the wild promaize growing on the plateaus of Mexico and Central America thousands of years ago. A towering prince of grasses it was, bearing its tiny seeds on loose spikes at the ends of the branches. Conditions changed. The perfect flowers separated into two kinds, bearing organs of the different sexes. A type with shortened side branches appeared, giving the seeds greater protection from feathered and furry enemies. This was probably the grain that some wise man among the forerunners of the Toltecs discovered and made the foundation of American agriculture. From that time forth cultivation made possible the selection of variations that would not have survived in the wild. Variation must have been plentiful, and our aboriginal corn breeders less foolish in agriculture than they were in commerce, as is demonstrated by the numerous varieties improved by long selection presented to the white man in return for a few paltry beads of colored glass.
- An endeavor to trace the exact path of the evolution of maize is beset with more difficulties than are indicated here. I agree with many of the conclusions of both Montgomery and Collins, whose excellent researches have given us a remarkable insight into the probable phylogenetic history of maize. I have endeavored to present in this paper only the probable way in which certain important jumps occurred, facts that might be supposed to be of more popular interest than a strictly botanical discussion.
- There are a large number of characters of less importance separating maize and teosinte that show that the two plants have developed along different lines after their separation from an ancestor more like both.