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Everyone who had the good fortune to be born in New England and to live in the country will treasure among the most pleasant reminiscences of his boyhood the recollection of his first visit to a "sugar bush." The sweet sap drawn through a magic spigot from a hole in the tree trunk; the boiling pot in which the sap was transformed into the most delectable of syrups; the transformation of the syrup into a wax of quite matchless flavor by pouring it on the snow-these are things that have no counterpart. They must be experienced to be appreciated, and no one who has experienced them is likely to forget them. To the unfortunate who has not been privileged to visit a sugar bush, the product of the maple is usually known only in its ultimate crystallized form in which it constitutes a brownish sugar of characteristic and delectable flavor. And I regret to say that many people who suppose themselves familiar with this product know it only in a diluted and adulterated form in which only a suggestion remains of the real maple quality. Nor does there seem to be much prospect of improvement in this regard, for, so far as I know, the maple tree is seldom or never cultivated for the garnering of its unique crop. The relatively small quantity of maple sugar that finds its way to the market is the product of trees that chanced to grow in the woodland and they are reserved not so much as sugar producers but as ultimate material for lumber. Yet maple sugar is a sweet of acknowledged quality, and one that deserves a larger measure of recognition as a commercial product than has hitherto been given it. Possibly the time may come when maple trees will be set out and cultivated for the production of sugar. But it is hardly likely that such cultivation of the maple can ever constitute a significant industry, because the product of a single tree is relatively insignificant. It is only the fact that the sugar maple has wood of such quality of fiber as to make it valuable for the cabinetmaker that could justify the cultivation of these trees as a commercial enterprise. On the other hand the amateur orchardist might do far worse than to set a row of maples, as ornamental trees about the borders of his orchard or gardens, regarding the capacity of the tree to produce a certain amount of sugar as an incidental attraction that adds to the value of a tree that otherwise is deserving because of its beauty of form and general attractiveness. The production of the sweet sap that has made the sugar maple famous gives this particular species exceptional interest among the members of a very meritorious family. Just why this species should have developed the capacity to produce so sugary a sap in such abundance, it would perhaps be difficult to say. A certain amount of sap may be drawn from the tissues of other maples, and even from the walnut and butternut, and in diluted form from the birches; but only the sugar maple produces sap of such quality as to be of real value.


And of course it is well known that the sugar maple itself has a "flow" of sap that is worth tapping, for a very brief period each season, just as winter is merging into spring. It is traditional at least among the makers of maple sugar that the sap runs best in those days of early spring when the sun shines brightly while there is a coverlet of snow on the ground. At this time, all that is necessary is to bore an auger hole in the trunk of the tree, and insert a spigot or grooved stick to guide the sap into a bucket. A single tree may be tapped in several places, and a bucket of sap will run from each spigot in the course of the day. The sap itself is a clear, watery fluid, the sweet taste of which gives assurance of the quality of the sugar it contains. By boiling the sap to evaporate the surplus water, a thick syrup is produced which crystallizes on cooling, producing the maple sugar of commerce. Nothing is added to the sap and nothing but part of its watery content is taken away from it-that is to say, if it is honestly made. The sugar as the maple supplies it, is a perfect product requiring no diluent and calling for no elaborate process of manufacture. Perhaps it is not so much matter for surprise that maple trees produce this sweet sap in such abundance as that other trees do not more generally imitate its example. For the function of the sugar in supplying nourishment for the young buds before the leaves are sufficiently expanded to begin their work of sugar manufacture is clearly enough understood. All other deciduous trees must supply nutriment in similar way to their growing buds. But in the case of other trees, either the sap will not flow in abundance or it is of such quality as to have no value. The manner of production of the sap may be more or less accurately inferred from what we have already learned of plant physiology. We know that the leaves of the tree metamorphose water and carbon into sugary substances which in turn are transferred to various parts of the plant to be stored, usually in the form of starch. In the case of the maple, we may assume that the carbohydrates, as they are manufactured in the leaf-laboratories, are transferred in the current of sap that flows downward from the leaves through branches and trunk as a countercurrent in the cambium until it finally finds its way to the roots of the tree and is there stored for the winter. When spring comes and it is time for the new leaf buds to put forth, the supplies of nourishment are retransformed into soluble sugars, dissolved in the water that is taken in by the rootlets, and transferred from cell to cell and along the little canals in the wood under the cambium layer of the bark, until they reach the twigs where the leaf buds they are to nourish are located. It is doubtless the so-called "root pressure" (which we have been led to interpret as due to osmosis) forcing the sap upward that causes it to flow from the wound in the tree made by the auger. To what extent the interference with the supply of nourishment that was being convoyed to the buds retards their development, might be interesting matter for observation. But this is something that does not greatly concern the sugar maker, and to which he doubtless never gives a thought. It is also interesting to conjecture whether it might be possible by selective breeding to produce a variety of sugar maple that will furnish sap in exceptional quantity and of unusual quality. The case is obviously different from that of the sugar prune or the sugar beet, both of which have been trained to increase their sugar content. But there is no doubt that different individual sugar maples differ widely in their sap producing, or at least in their sap rendering, quality. Presumably the difference may be due to the size of the root system. But so far as I know there are no accurate observations on the subject, nor has anything been done to determine whether a better race of sugar maples could be developed.


The extraordinary plant laboratories that manufacture sugars out of water and air is capable of transforming these sugars into many unusual substances, differing in character with the constitution of the particular plant. There are certain classes of juicy exudates, however, which appear to have characteristics that make them useful to plants of many types. Prominent among these are the milky juices that when dried constitute rubber, and the resinous ones that constitute tars and resins and turpentine. Nothing could be physically much more dissimilar than a piece of rubber and a teaspoonful of oil of turpentine. But the chemist tells us that each of these substances is composed exclusively of the two elements carbon and hydrogen; the only difference being that the turpentine molecule has 10 atoms of carbon and 16 of hydrogen, whereas the molecule of rubber has 8 carbon atoms and 7 atoms of hydrogen. Just how the elements are compounded, and just why they should make up substances of such unique characteristics when brought together in these particular proportions, even the chemist does not know. Nor, until recently, was he able to duplicate the feat of building up these complex molecules, even though he is perfectly familiar with the general properties of the atoms of both carbon and hydrogen. In very recent years, however, chemists have been at work on the problem of compounding the atoms in such a way as to get them together in the right combination to produce organic substances. And, although this work is only at its beginning, a good measure of success has been attained. In particular, the chemists of Germany and England have recently succeeded in combining carbon and hydrogen in the proportion of 8 atoms of the former to 7 of the latter and thus have produced an artificial rubber that is not merely an imitation rubber but is as truly pure rubber as if it had been produced in the cellular system of a plant. Indeed, the artificial product may be said to be somewhat more pure than the natural, inasmuch as the latter is more or less contaminated by extraneous products. Reference has elsewhere been made to the familiar feat of the chemist through which the famous dyestuffs, indigo and madder, have been manufactured in the laboratory, and manufactured so cheaply as to compete successfully with the natural product of the indigo and madder plants. What was a large plant industry only a few years ago has thus ceased to have importance. The indigo plant is still cultivated in the east, but the entire industry has been changed by the discoveries of the chemist. Only a few years ago a plant known as the tar weed (Madia), to which we have had occasion to refer in another connection, was gathered and its juices extracted for the making of the pigment madder. But it would not pay to undertake this work now, since the chemist has learned how to make madder from coal tar and hence has substituted for a plant industry an enterprise associated with the manufacture of gas. It will doubtless be a long time before the manufacture of artificial rubber makes corresponding encroachments on the industry of manufacturing rubber from the plant juices. Still it is quite within the possibilities that this may come to pass in the course of the coming generation. In the meantime, the rubber industry is a vastly important one, and the principal trees that supply the juices that on evaporating constitute rubber are cultivated in vast plantations in various tropical regions. Moreover rubber is gathered from wild trees of several species, although in recent years the cultivated trees have largely been depended upon to meet the growing needs of the industry. Trees of the genus Hevea are the most important source of rubber. But there are many other trees, the juices of which contain the essential constituents of rubber in the right combination, and a good many of these have commercial possibilities. I have referred in another connection to my experiments with tropical plants of the genus Asclepias, relatives of the familiar milkweed. I have undertaken tentative experiments to discover whether these plants might be developed to a stage that would make them commercially valuable as producers of rubber. The recent discoveries of the chemist make experiments in this line somewhat less valuable than they hitherto seemed. Yet the demand for rubber is so great, in these days of electricity and automobiles, that there seems little danger of overstocking the market. And if a plant could be developed that could be grown in temperate regions, and they would produce the rubber-forming juices in adequate quantity, such a plant would constitute a very valuable acquisition for a long time to come, even should natural rubber ultimately be supplanted by the laboratory product. The method of gathering the so-called latex, or milky juice, which is virtually rubber in solution, is curiously similar to the method of obtaining the sap of the sugar maple. Indeed the latex may be drawn in precisely the same way, by boring a hole in the trunk of the rubber tree and inserting a grooved stick along which the juice will run intova receptacle. But the cultivators are not usually content with so slow a method, and there are various methods of tapping the tree that expose a larger surface of the cambium layer and thus extract the milky juices in larger quantity. In the case of the wild trees it is not unusual for the natives of Mexico, Central America, and South America to make a series of "V" shaped incisions in the bark of the tree, placing a receptacle at the point of each "V" and thus securing a relatively enormous amount of fluid regardless of the fact that they jeopardize the life of the tree itself. Of course cultivated groves or plantations are tapped in a more conservative way, but the principle involved is everywhere the same. The latex of the rubber tree is comparable to the sugary sap of the maple. It appears to be a mere accident that this juice has the property of coagulating to form the substance called rubber which we now find so important. But this substance, obviously, as man uses it, has small place in the economy of the plant. Coagulated latex would serve no better purpose in the tissues of the rubber tree than would coagulated blood in the veins of a human being.


Of course the latex of the rubber tree might exude when the tree received an accidental injury, as from a falling limb, and in such case it would be advantageous to the tree to have the juice coagulate, just as coagulated blood is useful to a wounded man. In each case coagulation prevents excessive hemorrhage. Possibly this may explain the quality of the latex, its capacity to coagulate having been developed through natural selection. But under normal conditions, at least, the latex is always fluid, and its properties are little more like those of rubber than are the properties of the maple tree like those of sugar. Of course the same thing is true of the plant juices that when dried or partially evaporated constitute the various gums and resins. As manufactured in the tree they are transformed sugar products, and they are always in solution. Only when the juices are exposed to the air, as when they exude from an injured surface, do they coagulate to form the gummy or resinous substances that become articles of commerce. In some cases the exudate may be separated into two or more commercial constituents. Such is the case with the juice of those trees that produce turpentine. The liquid that flows from the tree, corresponding to the sap of the maple and the latex of the rubber tree, may be evaporated or distilled in such a way as to be changed in part to a solid gummy or even vitreous substance, and in part to the somewhat volatile fluid familiar as turpentine. Turpentine, unlike rubber, was known to the ancients, and was an extensive article of commerce in classical times. The original tree from which it was obtained is known as the terrebinth tree. It is a native of the islands and shores of the Mediterranean and western Asia. There are many trees, however, the sap of which has this resinous property, including most members of the family of conifers. The principal supply of crude oil, or common turpentine, in Europe, is obtained from the so-called sea pine, grown largely in France. The Scotch fir, the Norway pine, and the Corsican pine are other sources. In the United States the swamp pine and the so-called loblolly trees that grow in the swamps of North and South Carolina and Georgia, are the chief source of the commercial turpentines, although various other species are more or less utilized. A turpentine of peculiar quality that is highly prized for some industrial purposes is obtained from the balsam fir (A bies Balsamae), and is known as Canada balsam. Hitherto, the producers of turpentine have been found in the wild state, and no one, probably, has given a thought to the possibility of developing races of pines that produce an exceptional quantity of the resin-and turpentine-forming juices. But with the modern tendency to apply scientific methods to forestration in general, doubtless the question will ultimately arise as to whether the turpentine trees may not be improved along with the timber producers. That trees of the same species differ quite radically in the amount of the valuable juices is certain, so there would appear to be no reason why it may not be possible to develop varieties of trees that will be conspicuous for this quality, just as other trees have been improved as to their powers of growth or their capacity to produce abundant crops of fruit.


An incidental use of the resinous exudate of the pine tree that has come to assume considerable economic importance is the production of chewing gum. The habit of gum chewing appears to have originated or at least to have gained chief popularity in America in comparatively recent times. The resin that exudes from the spruce was the substance that was chiefly used, under the name of spruce gum, until somewhat recently. But of late years the chewing gum industry has reached proportions that make it impossible to meet the demand from this source. And it has been found that ordinary resin, combined with sugar and linseed oil, with some flavoring added, serves the purpose of the original spruce gum so the latter is now seldom seen in the market. More recently chicle, a gummy substance which exudes from several tropical trees, has been imported in great quantities, and is now supplanting all other sources of gum. The supplying of turpentine and its products gives the conifers high range among trees that produce commercial by-products of great importance. But with the exception of the pines, the trees that produce really important exudates or oils or chemicals are indigenous to the tropics, or at least are confined to the warm temperate zone. I have thought many times in recent years that I should like to have a plant laboratory in the tropics for the testing of tropical plants as to the production of useful commercial products, and for the development of improved varieties of plants the products of which are already utilized. It would be worth while, for example, to make very extensive experiments by way of testing the qualities of the different trees that deposit in their bark the bitter compound known as alkaloids, a galaxy of which are prized for their medicinal properties. These are very complex combinations of carbon, hydrogen, oxygen and nitrogen. That is to say, they have the same constituents as protoplasm itself and they differ from the gum and resins that we have just been considering in that each molecule contains at least one atom of nitrogen. The sugars, it will be recalled, occupy an intermediate place, inasmuch as they, unlike the resins and rubber, contain oxygen; but they contain no nitrogen. The formulae given by the chemist for the different alkaloids are intricate but they differ from one another only in the matter of a few more or a few less atoms of one or another of the four constituents ot' which they are all made up. There is, for example, only the difference of one atom of carbon and of four atoms of hydrogen between a molecule of quinine and a molecule of strychnine. Considering that the molecules comprise in the aggregate not far from fifty atoms, in each case, this discrepancy seems trifling. That the two drugs should have such utterly different effects upon the human system is a mystery that will be solved only when a much fuller knowledge is gained as to the physiological processes than anyone has at present. But the plant developer, of course, has no concern with this aspect of the subject. What interests him is the knowledge that different races of cinchona trees, for example, are known to vary greatly as to the proportion of commercial alkaloid deposited in their bark. And doubtless the same thing is true of most or all other producers of commercial alkaloids. Seemingly there is a splendid field, then, for the plant experimenter, could he establish a laboratory and experiment garden in the tropics, in the development of improved races of cinchona trees and of numerous other suppliers of medicinal alkaloids. The monetary return from such an enterprise would probably be larger than that which usually rewards the efforts of the plant developer in temperate zones, because the field is virgin, and because there is no present possibility of competition outside the tropics. It remains to be said that there are a few other trees and shrubs of our own latitude that may advantageously command the attention of the plant developer for the improvement of quantity or quality of the by-products of their life activities that man has found useful. It seems not unlikely that the horse chestnut, or buckeye, could be so educated as to become a profitable starch producer. At present this tree produces an abundant crop of nuts, but these are worthless because they contain a bitter principle that makes them inedible. Yet the nut of the horse chestnut is very starchy and if the bitter principle could be eliminated there is no reason why it should not prove both wholesome and nutritious. The West Indians sometimes grind the nuts to make meal. When this is soaked in water the poisonous principle is partially removed, and the residue is cooked and eaten. I have experimented somewhat in the attempt to test the western buckeye as to its possibilities of improvement. As long ago as 1877, I began work on this tree, and continued the experiments in a small way for a number of years. I observed that there was great variation as to productiveness of trees, as to size of nuts, and also as to bitterness of the nuts themselves. I am convinced that it would be possible to develop a variety in which the bitter principle would be greatly reduced in amount and perhaps altogether eliminated, and that at the same time a nut having a high starch content could be developed. It has been found possible with the South American plant called the casaba to utilize roots that contain a poisonous principle for the production of so important a commercial product as tapioca. It is not unlikely that the nuts of the horse chestnut, if developed until it had a still higher starch content, could be utilized in somewhat the same way, even though the bitter principle was not entirely eliminated. There are some members of the laurel family, also, that produce commercial products that make them perhaps worthy of attention. The camphor tree is too tender to be grown in our latitudes, but its relative, the sassafras, is a common tree throughout the eastern states, thriving even in New York and New England. Its bark furnishes the characteristic flavoring that is used for perfuming soaps and for similar purposes. The production of the sassafras would not constitute a significant industry under any circumstances, doubtless, yet there would be a measure of scientific interest in testing its capacities for improvement, and not unlikely new uses would be found for its product if it were made available in larger quantity. Another tribe that furnishes a product of a unique quality is that represented by a familiar wild shrub known in the eastern states as the wax berry or candle berry (Myrica cerifera) and sometimes also spoken of as the bay berry owing to the fragrance of its leaves. This shrub bears an abundance of small berries from which may be extracted a quantity of hard greenish fragrant wax, which was formerly much prized for the making of candles, and which has a certain value for the various other uses to which wax is put. A good many years ago while traveling in the east I found a candle berry bush that was of compact growth and that produced a large crop of waxy berries. I collected seed and brought it to California, and for several years worked on the shrub until, by selection, I had developed a variety that produced at least ten times as many berries and ten times as much wax as the average wild plant. At the same time I experimented with a Japanese member of the genus known as M. nagi or M. rubra, and also with the California species which is a tree growing fifty or sixty feet in height. I endeavored to cross the three Myricas in the hope of producing new varieties of value, but did not succeed, no doubt because the attempt was not carried out with sufficient pertinacity. The California species produces a wax of much darker color than the eastern one, but of about the same degree of hardiness. I still have several fine blocks of wax that were produced from these shrubs and trees during the time of the experiment. Although not successful in hybridizing the different candle berry shrubs, the experiments were carried far enough to show the possibility of great improvement by mere selection. If there were a market for the wax, the plant might be well worth improving. Even as it was, I advertised my improved variety of candle berry, but as no one cared to buy it, it was finally destroyed to make room for other shrubs. This is another case in which a product of intrinsic value has failed to find a market, largely, no doubt, because the plant that produces it has hitherto not been brought under cultivation, and hence has not produced a sufficient crop to bring it to the attention of the public and to create a market. It would not be surprising, however, if the candle berry should be thought valuable enough in future for development and cultivation on an extensive scale. For the wax that it produces is of unique quality, and it is almost certain to be found of value in connection with some commercial industry.

-Seemingly, there is a splendid field for the plant experimenter, could he establish a laboratory and experiment garden in the tropics for the development of improved producers of medicinal alkaloids.

This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 11 Chapter 8