Species and Varieties, Their Origin by Mutation Part 4

The color of the foliage and the size of the roots are extremely variable. Some have red leafstalks and veins, others a uniform red or green foliage, some have red or white or yellow roots, or exhibit alternating rings of a red and of a white tinge on cut surfaces. It seems only natural to consider the white and the red, and even the variegated types as distinct varieties, which in nature do not transgress their limits nor change into one another. In a subsequent lecture I will show that this at least is the rule with the corresponding color-varieties in other genera.

The fles.h.i.+ness or pulpiness of the roots is still more variable. Some are as thick as the arm and edible, others are not thicker than a finger and of a woody composition, and the structure of this woody variety is very interesting. The sugar-beet consists, as is generally known, of concentric layers of sugar-tissue and of vascular [69] strands; the larger the first and the smaller the latter, the greater is, as a rule, the average amount of sugar of the race. Through the kindness of the late Mr. Rimpau, a well known German breeder of sugar-beet varieties, I obtained specimens from seed of a native wild locality near Bukharest.

The plants produced quite woody roots, showing almost no sugar tissue at all. Woody layers of strongly developed fibrovascular strands were seen to be separated one from another only by very thin layers of parenchymatous cells. Even the number of layers is variable; it was observed to be five in my plants; but in larger roots double this number and even more may easily be met with.

Some authors have distinguished specific types among these wild forms.

While the cultivated beets are collected under the head of _Beta vulgaris_, separate types with more or less woody roots have been described as _Beta maritima_ and _Beta patula_. These show differences in the habit of the stems and the foliage. Some have a strong tendency to become annual, others to become biennial. The first of course do not store a large quant.i.ty of food in their roots, and remain thin, even at the time of flowering. The biennial types occur in all sizes of roots.

In the annuals the stems may vary from [70] erect to ascending, and the name _patula_ indicates stems which are densely branching from the base with widely spreading branches throughout. Mr. Em. von Proskowetz of Kwa.s.sitz, Austria, kindly sent me seeds of this _Beta patula_, the variability of which was so great in my cultures as to range from nearly typical sugar-beets to the thin woody type of Bukharest.

Broad and narrow leaves are considered to be differentiating marks between _Beta vulgaris_ and _Beta patula_, but even here a wide range of forms seem to occur.

Rimpau, Proskowetz, Schindler and others have made cultures of beets from wild localities in order to discover a hypothetical common ancestor of all the present cultivated types. These researches point to the _B.

patula_ as the probable ancestor, but of course they were not made to decide the question as to whether the origination of the several now existing types had taken place before or during culture. From a general point of view the variability of the wild species is parallel to that of the cultivated forms to such a degree as to suggest the multiple origin of the former. But a close investigation of this highly important problem has still to be made.

The varieties of the cultivated beets are commonly [71] included in four subspecies. The two smallest are the salad-beets and the ornamental forms, the first being used as food, and ordinarily cultivated in red varieties, the second being used as ornamental plants during the fall, when they fill the beds left empty by summer flowers, with a bright foliage that is exceedingly rich in form and color. Of the remaining subspecies, one comprises the numerous sorts cultivated as forage-crops and the other the true sugar-beets. Both of them vary widely as to the shape and the size of the roots, the quality of the tissue, the foliage and other characteristics.

Some of these forms, no doubt, have originated during culture. Most of them have been improved by selection, and no beet found in the wild state ever rivals any cultivated variety. But the improvement chiefly affects the size, the amount of sugar and nutrient substances and some other qualities which recur in most of the varieties. The varietal attributes themselves however, are more or less of a specific nature, and have no relation to the real industrial value of the race. The short-rooted and the horn-shaped varieties might best be cited as examples.

The a.s.sertion that the sundry varieties of forage-beets are not the result of artificial selection, [72] is supported in a large measure by the historic fact that the most of them are far older than the method of conscious selection of plants itself. This method is due to Louis Vilmorin and dates from the middle of the last century. But in the sixteenth century most of our present varieties of beets were already in cultivation. Caspar Bauhin gives a list of the beets of his time and it is not difficult to recognize in it a large series of subspecies and varieties and even of special forms, which are still cultivated. A more complete list was published towards the close of the same century by Olivier de Serres in his world-renowned "Theatre d'Agriculture" (Paris, 1600).

The red forage-beets which are now cultivated on so large a scale, had been introduced from Italy into France only a short time before.

From this historic evidence, the period during which the beets were cultivated from the time of the Romans or perhaps much later, up to the time of Bauhin and De Serres, would seem far too short for the production by the unguided selection of man of all the now existing types. On the other hand, the parallelism between the characters of some wild and some cultivated varieties goes to make it very probable that other varieties have been found in the same way, some in this country and others in that, [73] and have been taken into cultivation separately. Afterwards of course all must have been improved in the direction required by the needs of man.

Quite the same conclusion is afforded by apples. The facts are to some extent of another character, and the rule of the derivation of the present cultivated varieties from original wild forms can be ill.u.s.trated in this case in a more direct way. Of course we must limit ourselves to the varieties of pure ancestry and leave aside all those which are of hybrid or presumably hybrid origin.

Before considering their present state of culture, something must be, said about the earlier history and the wild state of the apples.

The apple-tree is a common shrub in woods throughout all parts of Europe, with the only exception of the extreme north. Its distribution extends to Anatolia, the Caucasus and Ghilan in Persia. It is found in nearly all forests of any extent and often in relatively large numbers of individuals. It exhibits varietal characters, which have led to the recognition of several spontaneous forms, especially in France and in Germany.

The differentiating qualities relate to the shape and indumentum of the leaves. Nothing is known botanically as to differences between [74] the fruits of these varieties, but as a matter of fact the wild apples of different countries are not at all the same.

Alphonse De Candolle, who made a profound study of the probable origin of most of our cultivated plants, comes to the conclusion that the apple tree must have had this wide distribution in prehistoric times, and that its cultivation began in ancient times everywhere.

This very important conclusion by so high an authority throws considerable light on the relation between cultivated and wild varieties at large. If the historic facts go to prove a multiple origin for the cultivation of some of the more important useful plants, the probability that different varieties or elementary species have been the starting points for different lines of culture, evidently becomes stronger.

Unfortunately, this historic evidence is scanty. The most interesting facts are those concerning the use of apples by the Romans and by their contemporaries of the Swiss and middle European lake-dwellings. Oswald Heer has collected large numbers of the relics of this prehistoric period. Apples were found in large quant.i.ties, ordinarily cut into halves and with the signs of having been dried. Heer distinguished two varieties, one with large and one with small fruits. The first about 3 and [75] the other about 1.5-2 cm. in diameter. Both are therefore very small compared with our present ordinary varieties, but of the same general size as the wild forms of the present day. Like these, they must have been of a more woody and less fleshy tissue. They would scarcely have been tasteful to us, but in ancient times no better varieties were known and therefore no comparison was possible.

There is no evidence concerning the question, as to whether during the periods mentioned apples were cultivated or only collected in the wild state. The very large numbers which are found, have induced some writers to believe in their culture, but then there is no reason why they should not have been collected in quant.i.ty from wild shrubs. The main fact is that the apple was not a uniform species in prehistoric times but showed even then at least some amount of variability.

At the present day the wild apples are very rich in elementary species.

Those of Versailles are not the same as those of Belgium, and still others are growing in England and in Germany. The botanical differences derived from the blossoms and the leaves are slight, but the flavor, size and shape of the fruits diverge widely. Two opinions have been advanced to explain this high degree of variability, but [76] neither of them conveys a real explanation; their aim is chiefly to support different views as to the causes of variability, and the origin of elementary species at large.

One opinion, advocated by De Candolle, Darwin and others, claims that the varieties owe their origin to the direct influence of cultivation, and that the corresponding forms found in the wild state, are not at all original, but have escaped from cultivation and apparently become wild.

Of course this possibility cannot be denied, at least in any single instance, but it seems too sweeping an a.s.sertion to make for the whole range of observed forms.

The alternative theory is that of van Mons, the Belgian originator of commercial varieties of apples, who has published his experiments in a large work called "Arbres fruitiers ou Pomonomie belge." Most of the more remarkable apples of the first half of the last century were produced by van Mons, but his greatest merit is not the direct production of a number of good varieties, but the foundation of the method, by which new varieties may be obtained and improved.

According to van Mons, the production of a new variety consists chiefly of two parts. The first is the discovery of a subspecies with new desirable qualities. The second is the transformation [77] of the original small and woody apple into a large, fleshy and palatable variety. Subspecies, or what we now call elementary species were not produced by man; nature alone creates new forms, as van Mons has it. He examined with great care the wild apples of his country, and especially those of the Ardennes, and found among them a number of species with different flavors. For the flavor is the one great point, which must be found ready in nature and which may be improved, but can never be created by artificial selection. The numerous differences in flavor are quite original; all of them may be found in the wild state and most of them even in so limited a region as the Ardennes Mountains. Of course van Mons preferred not to start from the wild types themselves, when the same flavor could be met with in some cultivated variety. His general method was, to search for a new flavor and to try to bring the bearer of it up to the desired standard of size and edibility.

The latter improvement, though it always makes the impression of an achievement, is only the last stone to be added to the building up of the commercial value of the variety. Without it, the best flavored apple remains a crab; with it, it becomes a conquest. According to the method of van Mons it may be reached within [78] two or three generations, and a man's life is wholly sufficient to produce in this way many new types of the very best sorts, as van Mons himself has done. It is done in the usual way, sowing on a large scale and selecting the best, which are in their turn brought to an early maturation of their fruit by grafting, because thereby the life from seed to seed may be reduced to a few years.

Form, taste, color, flavor and other valuable marks of new varieties are the products of nature, says van Mons, only texture, fles.h.i.+ness and size are added by man. And this is done in each new variety by the same method and according to the same laws. The richness of the cultivated apples of the present day was already present in the large range of original wild elementary species, though un.o.bserved and requiring improvement.

An interesting proof of this principle is afforded by the experience of Mr. Peter M. Gideon, as related by Bailey. Gideon sowed large quant.i.ties of apple-seeds, and one seed produced a new and valuable variety called by him the "Wealthy" apple. He first planted a bushel of apple-seeds, and then every year, for nine years, planted enough seeds to produce a thousand trees. At the end of ten years all seedlings had perished except one hardy seedling [79] crab. This experiment was made in Minnesota, and failed wholly. Then he bought a small lot of seeds of apples and crab-apples in Maine and from these the "Wealthy" came. There were only about fifty seeds in the lot of crab-apple seed which produced the "Wealthy," but before this variety was obtained, more than a bushel of seed had been sown. Chance afforded a species with an unknown taste; but the growing of many thousands of seedlings of known varieties was not the best means to get something really new.

Pears are more difficult to improve than apples. They often require six or more generations to be brought from the wild woody state to the ordinary edible condition. But the varieties each seem to have a separate origin, as with apples, and the wide range of form and of taste must have been present in the wild state, long before cultivation. Only recently has the improvement of cherries, plums, currants and gooseberries been undertaken with success by Mr. Burbank, and the difference between the wild and cultivated forms has. .h.i.therto been very small. All indications point to the existence, before the era of cultivation, of larger or smaller numbers of elementary species.

The same holds good with many of the larger forage crops and other plants of great industrial [80] value. Clover exhibits many varieties, which have been cultivated indiscriminately, and often in motley mixtures. The flower heads may be red or white, large or small, cylindric or rounded, the leaves are broader or narrower, with or without white spots of a curious pattern. They may be more or less hairy and so forth. Even the seeds exhibit differences in size, shape or color, and of late Martinet has shown, that by the simple means of picking out seeds of the same pattern, pure strains of clover may be obtained, which are of varying cultural value. In this way the best subspecies or varieties may be sought out for separate cultivation. Even the white spots on the leaflets have proved to be constant characters corresponding with noticeable differences in yield.

Flax is another instance. It was already cultivated, or at least made use of during the period of the lake-dwellers, but at that time it was a species referred to as _Linum angustifolium_, and not the _Linum usitatissimum_, which is our present day flax. There are now many subspecies, elementary species, and varieties under cultivation. The oldest of them is known as the "springing flax," in opposition to the ordinary "thres.h.i.+ng flax." It has capsules which open of themselves, in order to disseminate the seeds, while the ordinary heads of the [81]

flax remain closed until the seeds are liberated by thres.h.i.+ng. It seems probable that the first form or _Linum crepitans_ might thrive in the wild state as well as any other plant, while in the common species those qualities are lacking which are required for a normal dissemination of the seeds. White or blue flowers, high or dwarf stems, more or less branching at the base and sundry other qualities distinguish the varieties, aside from the special industrial difference of the fibres.

Even the life-history varies from annual and biennial, to perennial.

It would take us too long to consider other instances. It is well known that corn, though considered as a single botanical species, is represented by different subspecies and varieties in nearly every region in which it is grown. Of course its history is unknown and it is impossible to decide whether all the tall and dwarf forms, or starchy and sweet varieties, dented or rounded kernels, and hundreds of others are older than culture or have come into existence during historic times, or as some a.s.sume, through the agency of man. But our main point now is not the origin, but only the existence of constant and sharply differentiated forms within botanical species. Nearly every cultivated plant affords instances of such diversity. Some include a few types only, while [82] others show, a large number of forms clearly separated to a greater or lesser degree.

In some few instances it is obvious that this variability is of later date than culture. The most conspicuous case is that of the coconut.

This valuable palm is found on nearly all tropical coasts, in America, as well as in Asia, but in Africa and Australia there are many hundreds of miles of sh.o.r.e line, where it is not found. Its importance is not at all the same everywhere. On the sh.o.r.es and islands of the Indian Ocean and the Malay Archipelago, man is chiefly dependent upon it, but in America it is only of subordinate usefulness.

In connection with these facts, it abounds in subspecies and varieties in the East Indian regions, but on the continent of America little attention has as yet been given to its diverging qualities. In the Malayan region it affords nearly all that is required by the inhabitants. The value of its fruit as food, and the delicious beverage which it yields, are well known. The fibrous rind is not less useful; it is manufactured into a kind of cordage, mats and floor-cloths. An excellent oil is obtained from the kernel by compression. The hard covering of the stem is converted into drums and used in the construction of huts; the lower part is so hard as to take on a beautiful polish [83] when it resembles agate. Finally the unexpanded terminal bud is a delicate article of food. Many other uses could be mentioned, but these may suffice to indicate how closely the life of the inhabitants is bound up with the culture of this palm, and how sharply, in consequence, its qualities must have been watched by early man. Any divergence from the ordinary type must have been noted; those which were injurious must have been rejected, but the useful ones must have been appreciated and propagated. In a word any degree of variability afforded by nature must have been noticed and cultivated.

More than fifty different sorts of the coconut are described from the Indian sh.o.r.es and islands, with distinct local and botanical names.

Miquel, who was one of the best systematists of tropical plants, of the last century, described a large number of them, and since, more have been added. Nearly all useful qualities vary in a higher or lesser degree in the different varieties. The fibrous strands of the rind of the nut are developed in some forms to such a length and strength as to yield the industrial product known as the coir-fibre. Only three of them are mentioned by Miquel that have this quality, the _Cocos nucifera rutila_, _cupuliformis_ and _stupposa_. Among them the _rutila_ [84]

yields the best and most supple fibres, while those of the _stupposa_ are stiff and almost unbending.

The varieties also differ greatly in size, color, shape and quality, and the trees have also peculiar characteristics. One variety exhibits leaves which are nearly entire, the divisions being only imperfectly separated, as often occurs in the very first leaves of the seedlings of other varieties. The flavor of the flesh, oil and milk likewise yield many good varietal marks.

In short, the coconut-palm comes under the general rule, that botanical species are built up of a number of sharply distinguishable types, which prove their constancy and relative independence by their wide distribution in culture. In systematic works all these forms are called varieties, and a closer investigation of their real systematic value has not yet been made. But the question as to the origin of the varieties and of the coconut itself has engrossed the attention of many botanists, among whom are De Candolle in the middle of the last century, and Cook at its close.

Both questions are closely connected. De Candolle claimed an Asiatic origin for the whole species, while Cook's studies go to prove that its original habitat is to be sought in the northern countries of South America. Numerous [85] varieties are growing in Asia and have as yet not been observed to occur in America, where the coconut is only of subordinate importance, being one of many useful plants, and not the only one relied upon by the natives for their subsistence. If therefore, De Candolle's opinion is the right one, the question as to whether the varieties are older or younger than the cultivated forms of the species, must always remain obscure. But if the proofs of an American origin should be forthcoming, the possibility, and even the probability that the varieties are of later date than the beginning of their culture, and have originated while in this condition must at once be granted. An important point in the controversy is the manner in which the coconuts were disseminated from sh.o.r.e to sh.o.r.e, from island to island. De Candolle, Darwin and most of the European writers claim that the dispersal was by natural agencies, such as ocean-currents. They point out that the fibrous rind or husk would keep the fruits afloat, and uninjured, for many days or even many weeks, while being carried from one country to another in a manner that would explain their geographic distribution. But the probability of the nuts being thrown upon the strand, and far enough from the sh.o.r.e to find suitable conditions for their germination, is a very small one. To insure [86] healthy and vigorous seedlings the nuts must be fully ripe, after which planting cannot be safely delayed for more than a few weeks. If kept too moist the nuts rot. If once on the sh.o.r.e, and allowed to lie in the sun, they become overheated and are thereby destroyed; if thrown in the shade of other shrubs and trees, the seedlings do not find the required conditions for a vigorous growth.

Some authors have taken the fibrous rind to be especially adapted to transport by sea, but if this were so, this would argue that water is the normal or at least the very frequent medium of dissemination, which of course it is not. We may, claim with quite as much right that the thick husk is necessary to enable the heavy fruit to drop from tall trees with safety. But even for this purpose the protection is not sufficient, as the nuts often suffer from falling to such a degree as to be badly injured as to their germinating qualities. It is well known that nuts, which are destined for propagation, are as a rule not allowed to fall off, but are taken from the trees with great care.

Summing up his arguments, Cook concludes that there is little in the way of known facts to support the poetic theory of the coconut palm dropping its fruits into the sea to float away to barren islands and prepare them for [87] human habitation. s.h.i.+pwrecks might furnish a successful method of launching viable coconuts, and such have no doubt sometimes contributed to their distribution. But this a.s.sumption implies a dissemination of the nuts by man, and if this princ.i.p.al fact is granted, it is far more natural to believe in a conscious intelligent dissemination.

The coconut is a cultivated tree. It may be met with in some spots distant from human dwellings, but whenever such cases have been subjected to a closer scrutiny, it appears that evidently, or at least probably, huts had formerly existed in their neighborhood, but having been destroyed by some accident, had left the palm trees uninjured. Even in South America, where it may be found in forests at great distances from the sea-sh.o.r.e, it is not at all certain that true native localities occur, and it seems to be quite lost in its natural condition.

Granting the cultivated state of the palms as the only really important one, and considering the impossibility or at least great improbability of its dissemination by natural means, the distribution by man himself, according to his wants, a.s.sumes the rank of an hypothesis fully adequate to the explanation of all the facts concerning the life-history of the tree.

We now have to inquire into the main question, [88] whether it is probable that the coconut is of American or of Asiatic origin, leaving aside the historic evidence which goes to prove that nothing is known about the period in which its dissemination from one hemisphere to another took place, we will now consider only the botanic and geographic evidence, brought forward by Cook. He states that the whole family of coconut-palms, consisting of about 20 genera and 200 species, are all strictly American with the exception of the rather aberrant African oilpalm, which has, however, an American relative referred to the same genus. The coconut is the sole representative of this group which is connected with Asia and the Malayan region, but there is no manifest reason why other members of the same group could not have established themselves there, and maintained an existence under conditions, which are not at all unfavorable to them. The only obvious reason is the a.s.sumption already made, that the distribution was brought about by man, and thus only affected the species, chosen by him for cultivation. That the coconut cannot have been imported from Asia into America seems to be the most obvious conclusion from the arguments given. It should be briefly noted, that it was known and widely distributed in tropical America at the time of the discovery of that continent [89] by Columbus, according to accounts of Oviedo and other contemporary Spanish writers.

Concluding we may state that according to the whole evidence as it has been discussed by De Candolle and especially by Cook, the coconut-palm is of American origin and has been distributed as a cultivated tree by man through the whole of its wide range. This must have happened in a prehistoric era, thus affording time enough for the subsequent development of the fifty and more known varieties. But the possibility that at least some of them have originated before culture and have been deliberately chosen by man for distribution, of course remains unsettled.

Coconuts are not very well adapted for natural dispersal on land, and this would rather induce us to suppose an origin within the period of cultivation for the whole group. There are a large number of cultivated varieties of different species which by some peculiarity do not seem adapted for the conditions of life in the wild state. These last have often been used to prove the origin of varietal forms during culture.

One of the oldest instances is the variety or rather subspecies of the opium-poppy, which lacks the ability to burst open its capsules. The seeds, which are thrown out by the wind, in the common forms, through the apertures underneath [90] the stigma, remain enclosed. This is manifestly a very useful adaptation for a cultivated plant, as by this means no seeds are lost. It would be quite a disadvantage for a wild species, and is therefore claimed to have been connected from the beginning with the cultivated form.

The large kernels of corn and grain, of beans and peas, and even of the lupines were considered by Darwin and others to be unable to cope with natural conditions of life. Many valuable fruits are quite sterile, or produce extremely few seeds. This is notoriously the case with some of the best pears and grapes, with the pine-apples, bananas, bread-fruits, pomegranate and some members of the orange tribe. It is open to discussion as to what may be the immediate cause of this sterility, but it is quite evident, that all such sterile varieties must have originated in a cultivated condition. Otherwise they would surely have been lost.

In horticulture and agriculture the fact that new varieties arise from time to time is beyond all doubt, and it is not this question with which we are now concerned. Our arguments were only intended to prove that cultivated species, as a rule, are derived from wild species, which obey the laws discussed in a previous lecture. The botanic units are compound ent.i.ties, and [91] the real systematic units in elementary species play the same part as in ordinary wild species. The inference that the origin of the cultivated plants is multiple, in most cases, and that more than one, often many separate elementary forms of the same species must originally have been taken into cultivation, throws much light upon many highly important problems of cultivation and selection. This aspect of the question will therefore be the subject of the next lecture.