PLANTS WHICH YIELD USEFUL CHEMICAL SUBSTANCES
OBSERVATIONS ON SUGAR-CANE, HOPS AND SUGAR-BEETS
An English physician residing in Trinidad made a casual observation that proved enormously important to the growers of sugar-cane. The physician observed that in the cane fields there were little grass-like plants coming up here and there. The planters whom he asked about it said that it was "grass", and let the matter go at that. But the physician had a suspicion that each blade of grass was really the shoot of a seedling sugar-cane plant. As it chanced both the planters and the physician were right. The little shoots were young sugar-cane plants; but of course sugar-cane is itself a giant grass, so there was no mistake. But the planters had not a suspicion as to what kind of grass the shoots were; so when the physician took some of them up and cultivated them, and they were seen to develop into stalks of sugar-cane, everyone except the physician himself was greatly surprised. For it had been supposed that the sugar-cane does not produce seed, and such a thing as a seedling sugar-cane was hitherto unheard of. The sugar-cane does, in point of fact, belong to that comparatively small company of cultivated plants that have almost totally given up the habit of seed-production. We have seen that the horseradish is another plant that has similarly stopped producing seeds, and that the common potato has almost abandoned the habit. Comment has been made, also, on the rather extraordinary character of this departure from the most sacred traditions of plant life. That an organism, whose sole purpose beyond the perpetuation of its own individual existence might be said to be the production of seed, should continue to grow and thrive and yet should totally abandon the habit of seed-production seems altogether anomalous. The explanation is found, as we have seen, in the fact that man provides means for the propagation of horseradish and sugar-cane by division of roots or by transplantation of cuttings. In the case of the potato, nature herself has provided tubers that take the place of seeds in a measure; and we have seen that there is a curious reciprocal relation between the formation of seeds and the formation of tubers, under certain circumstances. In certain cases, for example, the growth of the roots of a plant or even of the plant stem may be promoted by the removal of the blossoms. We saw this illustrated in the case of the huckleberry. We saw also how the potato that was grafted on the stem of a tomato might grow aerial tubers from the axils of the leaves in the position that would normally be occupied by the flowers-and ultimately by seeds, had not the potato given up the habit of seed production. Another illustration of the affinity between bulbs and flowers is shown by the onion, which sometimes grows a bulb at the top of its stalk, to perform the function of seeds in storing nutrient matter and at other times divides at the base like many other similar plants to form off-shoots from which the new plant will grow in another season. But in all these cases nature is substituting one means of reproduction for another, or supplementing one means with another, and the essential purpose of race preservation is not for a moment overlooked. In the case of the sugar-cane, however, it might almost be said that nature has abandoned the idea of provision for the multiplication of the species, and has left the matter entirely to man. For in giving up the habit of seed-production, the sugar-cane has developed no complementary habit of bulb production. It is propagated by cuttings, but the agency of man is necessary to place those cuttings under proper condtions for growth. Left to its own devices, the cane would be likely to give an illustration of race suicide.
REJUVENATION THROUGH SEED PRODUCTION
All this, however seems out of harmony with the illustrative case which we began. For obviously the Trinidad physician could not have found seedlings of the sugar-cane unless the sugar-cane produces seed. In point of fact, it does produce seed on rare occasions, but the habit has been so nearly abandoned that most cultivators of the plant supposed that it had given up altogether. The Trinidad case, however, shows that Nature is not altogether abandon the sugar-cane to the good graces of man. She still on occasion stimulates the plan to a revival of its long forgotten custom. And the benefits that result from such revival will be obvious if we follow a little farther the story of the grass-like seedlings that the physician dug up in the cane-fields of Trinidad. It appears that one of these seedlings, grown to maturity, was carried subsequently to the Hawaiian Islands, and there propogated in the usual way, so that in due course sufficient plants were grown from it to be tested as to their qualities of growth and sugar production. And it was soon discovered that the progeny of this seedling constituted virtually a new race of sigar-cane; one that would grow on land so poor that it had been allowed to remain fallow. the new variety, indeed, would produce more sugar even on the poorest land which had been abandoned, than the ordinary variety produces on the best land. Being taught by this experience, the growers of sugar-cane paid heed to the seedlings in the fields where they appeared, and subsequently raised from seed, and distributed in all countries, new varieties of sugar-cane that have probably increased the sugar production of the world by millions of tons each year. One could not ask a better object lesson in the possibility of rejuvenating a static race of plants through the growing of seedlings. I first made experiments with seedling sugar-cane in my own gardens, and when reports of these were made, I reveived letters from the various sugar-growing regions of the world, asking for further information, and now there are several well equipped experiment stations engaged in the work of raising and testing sugar-cane seedlings.
APPLYING THE NEW KNOWLEDGE
The reader will at once recall the case of the Burbank potato, which is in all respects comparable. There, also, a plant that ordinarily does not produce seeds was found by exception to be fertile, and the plants grown from the seed showed the widest departure from the frm of the parent plant, and constituted the progenitors of a new and improved variety. The obvious explanation is that the seeds owed their existence to the union of two plant strains, one represented by the pollenate and the other by the pistillate flower, that must be somewhat divergent. The bringing together of the two racial strains results, as we have seen illustrated over and over, in the giving of renewed vigor or vitality of the offspring, and in the production of variation through the new assorting and recombination of characters, some of which may have been latent and unrevealed in one or both parents. In the case of the sugar-cane, propogation by cuttings had been the universal custom with the planters for no one knows how many generations. As a result, a single cultivated variety of cane that chanced to be in existence when the practice of propagation by cutting was established continued unchanged as to its essential characteristics, and there was no apparent opportunity for any modification, except such minor ones as might result from increased or diminished nutrition due to the precise character of the soil and climate. But the chance finding of the seedlings put the plant on a new basis, and gave the planters new varieties that enabled them to improve the cane, and bring it more in line of competition with the rival sugar-producer that had only recently come into notice, namely the sugar-beet. At the time when custom of propogating cane by cuttings was established this plant stood in a class quite by itself as a sugar-producer. But within the past fifty years the merits of the sugar-beet have come to be understood. The possibility of developing a beet with a high sugar content has been established, and the beet sugar indutry has risen to such proportions that it more than rivals the cane industry. stimulated by the unexpected competition, which threatened to annihilate the case sugar industry, somewhat as the work of the synthetic chemist has practically annihilated indigo growing and madder growing, the planters have in recent years given serious attention to the question of the possible improvement of the sugar-producing qualities of the cane. Several experimentors from different parts of the world have written me concerning this matter within the past fifteen years. And a number of my friends and acquantances are now raising sugar-cane from seed in Mexico, the Hawaiian Islands, and Cuba, with an eye to the production of improved varieties. Their efforts should be successful. Crossbreeding the sugar-cane will give it new vitality, and careful selection from among the new varieties that will appear in the second generation should enable the cultivators to develop new strains of the sugar-bearing cane that will be far richer in sugar content than any of the old varieties. The cane is at best handicapped in competition with the beet by the fact that it can be grown only in tropical and sub-tropical climates. If it is to hold its own, it must be developed to its full possibilities of productivity. Doubtless it will be possible to develop races of sugar-cane having greatly increased size of stalk, and having also a higher percentage of sugar in a given quantity of pulp. In attempting such developments, the experimenters are merely bringing the sugar-cane industry into line with the other great plant industries, most of which were neglected by the scientific plant developer until very recent years. My own experiments with the cane have not extended beyond the greenhouse, but I have found that the seed germinates readily there, although only a few seeds out of a handful may grow; the contrast in this regard being a very striking with the seed of the allied Pampas-grass, which is as dimunitive as that of the sugar-cane and not dissimilar in appearance, but which germinates promptly almost to the last seed.
ALLIES OF THE SUGAR-CANE
I have experimented more extensively with certain relatives of the sugar-cane of the tribe of sorghums. This included not only the sorghums that produce the syrups, but also broom-corn, Kaffir corn, and a score or so of allied plants, some of which have great value as fodder plants. The best known of the sorghums shows its relationship with the sugar-cane in that it produces a syrup which, although not of the same chemical composition as cane sugar, is very sweet and palatable. Sorghum differs very radically on the other hand from sugar-cane, in that it is a hardy annual plant. It came to us from China but probably originally from South Africa, and it proved adaptable to our soil and climate almost everywhere. It is grown in practically every state in the Union, for syrup making. It is known also as a forage plant of very great value, and its stalks supply fodder for the farm animals. It will be gathered from this that the sorghum is a much less specialized product than the cane, and that it retains its full vigor as a seed producer. Partly as a result of its cultivation in widely different regions of the globe, and partly no doubt through conscious and unconscious selection on the part of its cultivators, the sorghum has developed many varieties, which are divided into three quite distinct groups. One type of sorghum is the syrup-producer to which we have just referred. The other type constitutes a very valuable forage and grain-producing plant, not altogether unlike Indian corn in general appearance, that is almost devoid of sugar. The third typoe resembles the others in some respects, but the kernels are smaller and more primitive in form, the plant being used for the manufacture of brooms. My own work with the sorghums has included a good many different varieties, but has chiefly concerned the non-saccharine types, and, in particular, the one known as broom-corn. This is a variety of sorchum having long, slender panicles of a specialized form, produced by long selection for the special purpose of making brooms and brushes. The product of this plant is familiar in every household, but the plant itself has not been generally known in the United States until of late. There is a vast difference in the different varieites as well as individual plants of broomcorn as regards length, strength, and symmetry of the group of panicle stems, or brush as it is technically called, and equal diversity as to the quantity produced per acre. My experimental work with the broom-corn has been directed toward the development of a long, and in particular straight, panicle stem. Most of the broom-corns have long but crooked stems-that is, stems with crooks or crinkles near the base. Moreover, most of the broom-corns under cultivation vary as to the quality of the brush, some of them being long, some short, and there being a corresponding deversity as to color. I have succeeded, in a few generations of selective breeding, in greatly increasing the number of straight stems of the brush, and giving them a more shapely form. The broom-corn responds readily to selection and care. My experiments were made by selecting seed from the plant or plants in a lot that showed the best individual characteristics. Attention was paid not merely to the brush itself, but also to the stalks of the plant. There is obvious advantage in growing a large, long brush on a dwarfed stalk, that as little plant energy as possible may be used for the production of the stalk, the chief supply beingreserve for the more important brush. It was found very difficult, but not impossible, to improve the plant along both lines simultaneously, as it seemed to be working in opposite directions. I was also able to develop a brush that had improved qualities of firmness and durability, combined with pliable texture. The syrup-producing sorghums are chiefly of two very closely related types, which are usually spoken of as Amber and Orange sugar-canes. Individual plants vary a good deal as to their sugar content and other characteristics. My experiemnts with the syrup-producers have shown that there is a great diversity in the individual plants as to the amount of saccharine substance in their tissues; and that it is possible by careful and systematic selection through successive generations to increase the sugar content, as has been done with the sugar-beet, and is being done with the sugar-cane. My work, however, has not extended beyond the experimental stages. I satisfied myself as to the feasibility of the project; it should be carried to completion by someone working under the auspices of the Government or an Agricultural Society where abundant acreage and intelligent help are available. The work is important, for the syrup-bearing sorghum is a plant of real value, and there is a great demand for its product. But the work of developing the plant does not offer commercial inducements that make it profitable for the private investigator to devote a large amount of time to it.
SOME CURIOUS CARBOHYDRATES
The differences between the sweets extracted from the sugar-cane and those taken from the sorghum are very obvious and tangible. One plant supplies a juice that when boiled and evaporated and refined gives a fine granular product familiar to everyone as sugar. The juice of the other plant, somewhat similarly treated, constitutes a syrup of varying color, which is exceedingly sweet and palatable, but which it could by any chance be mistaken for cane-sugar. Yet the chemist tells us that the sugar content of the juices of these plants is in each case a compound made up exclusively of three elements-carbon, hyrdrogen, and oxygen-and that the differences observed are due to modifications in the proportions in which the different elements are compounded. It appears that sugar of the glucose type, as represented in the syrup of the sorghum, is a much more simple compound than cane sugar. The Glucose has only 6 atoms of carbon while cane sugar has 18; it has 12 atoms of hydrogen only, whereas cane sugar has 32; and 6 atoms of oxygen, in contrast with the 16 atoms of the cane-sugar molecule. We have elsewhere seen that starch is a compound of the same elements; differing, indeed, from glucose only in that it has 10 hydrogen atoms instead of 12, and 5 oxygen atoms instead of 6. Stated in chemical terms, a molecule of starch that has had a molecule of water incorporated with its substance in a chemical union, becomes a molecule of glucose; and, of course, the converse holds-a dehydrated molecule of glucose becomes a molecule of starch. But to build up a molecule of cane sugar from either starch or glucose requires the introduction and incorporation of many individual atoms, although no new kinds of atoms are required. It is simply that the molecule of cane sugar is a very much more intricate structure, made of the same material. The glucose molecule is, if you will, a simple dwelling; the cane sugar molecule an elaborate mansion. But the materials with which they are compounded are precisely the same. There is a good deal of uncertainty on the part of the chemists as to the exact way in which the various molecules of the different sugars and allied carbohydrate substances are built up. Some chemists regard a molecule of a substance called methyl aldehyde, which consists of a single atom each of carbon and oxygen combined with two atoms of hydrogen as the basal form of carbon compound which the chlorophyll in the plant leaf makes by bringing together an atom of carbon from the atmosphere and a molecule of water. From this relatively simple carbon compound more elaborate compounds are built, through the introduction of varying numbers of additional atoms of carbon or hydrogen or oxygen, as the case may be, and all of the intricate juices and flavors and sweet and bitter principles of the various plants are thus compounded in the marvelous laboratory of the plant cell.
THE PRODUCT OF THE HOP
Among the multitudes of compounds of the almost endless series in which carbon, hydrogen, and oxygen are joined through the agency of the plant cell, there is one that is of peculiar interest from the standpoint of the agriculturist, because it gives value to a plant that otherwise would be at best a troublesome weed, to be ignored and despised. The carbon compound in question is the bitter principle known as lupulin or humulin, which is the really important constituent of the flower of the hop. This so-called alkaloid, with its exceedingly bitter taste, would never be suspected by any one but a chemist of having the remotest relationship with sugar; yet, in point of fact, it is made of precisely the same elements that make the sweet content of the sugar-cane's delectable juices. But the three essential elements are differently assorted, as any one might readily surmise who contrasts the bitter taste of the hop with the sweet taste of sugar. In point of fact, there are 32 atoms of carbon, and 50 atoms of hydrogen, with only 7 atoms of oxygen making up the composition of the alkaloid that gives the hop value. No one knows precisely what is the share of each element in giving any particular quality to a plant product. The chemist at present can only tear down the molecular structure and tell us of what it is composed. In the presence of the elaborate carbon compounds that are represented by such substances as sugar and lupulin, he is like a barbarian standing before a beautiful temple. The barbarian could tear down the temple, but he could not rebuild it. Similarly the chemist can tear the carbohydrate molecule to pieces, but he cannot put it together again. He knows how to pull to pieces the molecule of sugar, for example, making it into a simpler form of sugar, but he cannot build up even the simplest form of sugar from elementary atoms, were these ever so freely supplied him. Carbonic acid is everywhere in the air, and water may be had for the asking. The chemist knows just how many molecules of water he should take to combine with just so many atoms of the carbon to make a molecule of sugar or a molecule of lupulin. But he does not know how to go about the task. His only resort is to appeal to the agriculturist in the field, who deals with living laboratories in which the method of compounding these intricate substances is understood. If the chemist would have sugar, he must seek it in the product of the cane or sorghum, or beet. If he would have lupulin, he must go to the hop vine, for this plant alone has learned the secret of its production. So it chances that the ancient calling of the agriculturist is as essential today as it has always been; and that it is necessary now as always heretofore to cultivate different varieties of plants in order to gain the diverse products that man needs or desires as food or as aids in the industries. The particular product that a hop vine grows, and in the production of which it has an absolute monopoly, is used, as everyone is aware, by the brewer in the process of the manufacture of beer. He has been able to find no product that makes a satisfactory substitute for the bitter principle supplied by the lupulin of the hop. The particular place in which the hop vine stores this bitter alkaloid, once it has manufactured it, is the curious cone-like leafy seed-case or envelope of the pistillate flower. Without doubt the plant develops this bitter principle and stores it there to give the seeds protection from the depredations of animals. But whatever its purpose, the bitter alkaloid provided by the hop was discovered at an early date to have value for the purposes of the brewer, and the hop vine continues to be grown in large quantities solely for the production of this alkaloid. The hop vine belongs to that somewhat numerous tribe of plants that grow the pistillate and staminate flowers on different vines. It is only the pistillate flower that is of value to the hop grower. But a few staminate flowers are grown here and there in the field to fertilize the others, the cultivators feeling that the seed which would not otherwise be produced has at least the value of adding weight to the flower heads, and probably it adds lupulin also. The hop has been grown from prehistoric times, and the exact country of its origin is not known, although it is found growing wild in Colorado and New Mexico in the high mountains where it cannot have escaped from cultivation. But comparatively little has been done in the way of developing it, and there is good opportunity for work in this field. It goes without saying that different strains of hop vines differ in productivity, and in the amount of lupulin that their flowers secrete, and in the quality of the product. Certain Bavarian hops have lupulin of peculiarly fine flavor, but these are all less productive than the hops grown in America. Following out the principles of plant development repeatedly presented, it may be assumed that the hop can be improved as to productivity and alkaloid content and the quality of the latter by selection. Presumably improvement could be facilitated by hybridization. The plant is one that can readily be experimented with, and it should attract the attention of some one living in a region where this plant is extensively cultivated. It is well to bear in mind the staminate parent, and to test its strain of productivity.
The possibilities of stimulating a plant to outdo itself in the production of its characteristic carbon compounds are well illustrated by the story of the sugar-beet. It was not much over a half century ago that the merits of this vegetable as a producer of sugar began to be seriously considered. The fact that sugar-cane grows only in warm climates, and that here is a hardy plant that may be grown anywhere within the temperate zone, stimulated the older Vilmorin brothers of Paris, France, who had learned that the beet produces a sugar chemical identical with that of the sugar-cane, to make inquiry as to whether it might not be possible to grow the beet on a commercial scale, and extract its sugar in competition with the product of the cane. For a long time the attempt was not attended with great success. But it was finally demonstrated that the sugar-beet, even in its undeveloped form, could be made available as a supplier of sugar on a commercial scale, and then the attempt began to be made to develop varieties of beet having a larger sugar content. It is said that the beets at first used contained only about six per cent of sugar. But by careful selection through a series of generations it has proved possible to increase the sugar content of the beet, just as the length of fiber of the cotton-boll was increased, merely by paying heed generation after generation to the individual plants that showed the best qualities, and saving the seed of these plants only for the raising of future crops. Year by year the sugar content of the best varieties of beets was increased until from six percent it had advanced to twenty percent, and in the case of some individual beets even to thirty-five percent; and in a few cases as high as thirty-six percent has been secured from whole fields of beets in Colorado. This should be a wonderful stimulant to plant developers everywhere. There is perhaps no other case so widely known or involving such large financial interests in which a corresponding improvement has been made in a commercial plant within recent years. My own share in this work has been, until quite recently, that of an adviser rather than that of a direct experimenter. Some twenty years ago I was asked by the sugar-beet manufacturers of both Europe and America to take up the improvement of the beet. But while I gladly advised in the matter, and pointed out the lines of development through which further improvement might be expected, was unable to give personal attention to experiments with the beet, owing to the pressure of almost numberless other lines of investigation. More recently, however, I have experimented with varieties of the beet that were already very greatly improved, working with seeds supplied by prominent beet raisers who had developed their product by combining the qualities of ten or more varieties of Russian, German, French, and English sugar-beets. The crossbreeding experiments through which I was endeavoring to increase still further the capacity of the beet for sugar were, for reasons already several times repeated, neglected. But, so far as they progressed, they fell in line with almost numberless other series of experiments in plant development, and gave promise of the production of a beet that would have a higher sugar content than any beet hitherto under cultivation. Just what may be the limit to the percentage of sugar that the beet can be expected to develop would be matter of mere conjecture, but that it will represent a considerable advance upon the percentage already attained is scarcely open to doubt. And even as the case stands, the sugar-beet has attained a position in which it is, as we have already seen, a dangerous rival for the sugar-cane. The producers of sugar-beets have been at work while the producers of sugar-cane were sleeping; and the results of their efforts constitute a triumphant demonstration of the value of scientific plant experimentation as an aid to the practical agriculturist.
This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 8 Chapter 5