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The chemical content of the cactus slabs depends largely on the variety and also to a certain extent upon the age of the slabs. The young shoots in the early period of their growth have a very high water content, as is the case with all succulent herbage. The amount of crude fiber in the leaf at this stage may represent less than one percent of the total bulk. On the other hand, the old slabs and the main stalk of the plant take on a growing percentage of woody fiber, which renders them less and less palatable, but which adds to their value from another standpoint, as will appear presently. The slabs during the period of their best development, when they would ordinarily be used for forage, contain, according to chemical analysis, from 2.71 percent to 4.6 percent of starch and its equivalent, with from .58 percent to .72 percent of protein, and .96 percent to 1.68 percent of mineral salts. There is also a very small amount of fat, which like the other nutritious elements is being increased in quantity in some of the newer varieties. The varying amount of these food constituents suggests that the quantity may be considerably increased by selection. Of course the same thing is true of the other constituents. No doubt the protein content, for example, may be increased by selective breeding, just as we have seen done in the case of corn. And in general the constituents of the Opuntia slabs that give them food value may doubtless be increased by careful combination and selection. Hitherto the development of the plant has been carried along the lines of spinelessness and great size and productivity; although, even as the case stands, there has been a considerable improvement in the percentage of food constituents. In particular the variety Chico shows such advance upon the other varieties, notably the Santa Rosa, in its percentage of mineral salts as to suggest still greater possibilities of development in this direction, although in some respects the Chico is not an exceptionally good variety. In general the solid content of the Chico variety is 2 percent greater than that of the Santa Rosa. Such variation is not surprising, but it is sufficient to show that there are possibilities of selection through which the Opuntia is given additional food value. Even at the present time, however, the slabs of the Opuntias furnish fodder of highly nutritional character. That there is also a high water content is no disadvantage in a plant growing in arid regions. On the contrary, we have seen that this is to be regarded as one of the greatest merits of the plant, inasmuch as it enables animals to secure their water supply by eating the slabs, thus maintaining health and growth even when no drinking water is available for months together. The qualities of the cactus fruit have been dealt with in an earlier chapter. It will be recalled that there are numerous varieties of fruit, differing almost as widely as the varieties of apples. The essential character of all the fruits of the improved varieties, however, is a peculiar juiciness of pulp, combined with individuality of flavor and in some cases a slight trace of acid. The fruit of the wild Opuntias has sometimes been characterized as lacking flavor. But constant attention has been paid to the bettering of the fruit and the fruit of the new varieties is popular with all those who are acquainted with it. On my grounds the choicest varieties of fruits of many kinds are grown, but the workmen usually prefer the fruit of the Opuntias to any other that is in season at this same time. The improved fruits are rapidly gaining in popularity in the markets. When shipped to the east they bring about the same price as the best oranges, and the fact that they can be produced at a fraction of the cost of growing the orange should give them importance from the standpoint of the orchardist. Reference has been made also to the fact that the fruit has excellent qualities for making preserves and jams and jellies. The scarlet and crimson varieties have value in supplying coloring matter for other fruit preserves, ices, and confections. This newer vegetable pigment, with its beautiful shades of color, should largely supplant the objectionable analine dyes that are now generally used to color ices and confections and non-alcoholic beverages.


In countries where the cactus grows abundantly, it has long been known that its young slabs make a palatable form of greens when cooked. In recent years some scientific experimenters have made the attempt to test the food value of the leaves of the partially improved cactus. The cactus leaves when fried are a substitute for some of the poorer vegetables. Tender leaves should be selected, the skin peeled off, and the plants fried rapidly in butter. Appetizing preserves may be made from the fruit, somewhat after the manner of apple butter. The fruit itself may be dried and thus preserved for winter use. With the production of 100 tons an acre, there is opportunity to preserve the fruit on a commercial scale, if a sufficient market for it can be developed. To me it seems that the cooked fruit lacks the fine flavor of the raw fruit. In general the fruit may perhaps be served to best advantage as a salad. But I have on several occasions had jars of delicious jams, made from cactus fruit, sent me from different localities. The fact that the fruit of the perfected Opuntias contains a high sugar content, amounting sometimes to from 12 to 16 percent, makes it obvious that this plant might be used for the production of methyl alcohol. The slabs may be used for the same purpose, and the enormous productivity of the plant would make amends for the comparatively low percentage of fermentable starch in its composition.


It has been estimated that the improved Opuntias produce foliage and fruit so abundantly that they could be grown advantageously on land that cost even one thousand dollars per acre. Analyses made by the Agricultural Department of the State University of California have shown that the new varieties greatly exceed the old ones in nutritive qualities. Yet even the undeveloped Opuntias have long been recognized, particularly by the peoples of the Mediterranean, as having high food value. The importance of the new plants as suppliers of food for human beings, in regions subject to occasional or habitual shortage, has been recognized by several governments. The German Government in recent years has tested the new Opuntias at several places in its possessions in Africa. In parts of India where famines threaten and from time to time destroy millions of people, the spineless cactus is being planted for the purpose of tiding the people over in the years of famine, even if not used as a part of the regular dietary. The English Government is testing the new plants in Egypt and India. The plants have been sent to Australia. They are also being tested in Argentina and in other parts of South America. The new Opuntias differ from almost every other plant, and may be said in a way to resemble canned food, in that their food content remains in perfect condition on the plants year after year until needed. Nothing more is required than to plant the Opuntias, and fence them against the encroachment of animals. It is not necessary to cultivate them, although it is advantageous during the first two or three years, nor need any attention be paid them until their slabs are needed. They would thus grow enormously and when the occasion arose they would supply an almost indefinite quantity of food to meet the needs of a population that otherwise must die of starvation. The value of a plant that need not be cultivated and needs no preparation yet which will perpetually hold in reserve a colossal quantity of food per acre, constantly adding to it (the annual increase being measured in scores or even in hundreds of tons), offers a refuge to populations that are threatened with years of drought and failure of cereal crops that is not duplicated by any other food produced hitherto under cultivation. Even if the new spineless Opuntias had no other function than this, the time and labor devoted to their production would obviously be repaid a million fold.


There is one curious property of the slabs of the Opuntias that to some extent militates against their popularity as foodstuffs. This is the fact that the leaves contain a mucilaginous substance, the quantity of which, however, varies widely with the different varieties. The varieties that contain less of the mucilage are used by the Mexicans for the making of confectionery. Some of the finest confections of Mexico are candied cactus leaves. The leaves also make excellent pickles, the only drawback to which is the presence of the mucilage in the case of some varieties. Those that lack the mucilage make pickles as fine in flavor as the best cucumber pickles. On the other hand, the mucilage, while undesirable from one standpoint, is not without its value. It may be extracted by cutting the leaves in thin slices, and placing them in water. One or two slabs will make a gallon of good, thick, perfectly transparent mucilage. When this substance dries slowly, it produces a gum that is generally white or of a pearly color, and not easily dissolved in water. The mucilage is often used locally to mix with whitewash, to which it gives something of the permanency of a paint. It is also used at times for stiffening sleazy cotton goods, and for water-proofing cloth. Beyond this the economic uses of mucilage have not been developed. But sooner or later someone will find use for this by-product of the cactus, for the dressing on a large scale of fabrics, or any one of the hundred purposes to which mucilaginous substances are put. I myself have made tentative experiments to test the qualities of the mucilage, but these have not been carried far enough to produce conclusive results. The Opuntias have possibilities of a quite different character, connected not with their juices or pulp, but with the woody fiber which makes a network in the older leaves, and which comes to form the main substances of the central stalk. It has been found that this woody network, when the pulp is removed, makes a clean white fiber that is in the most beautiful condition for paper making. The older stems and roots furnish the fiber in considerable quantities, and even the roots are available for the purpose. The amount of paper stock varies much in the different species. The expert estimate of the fiber as a stock for the making of the finest paper, including bank note paper, has been so enthusiastic that it might be well to devote attention to the breeding of some of the spineless Opuntias with an eye to the development of the fiber, so that this by-product of the plant may become of value as a source of paper stock; also for the making of leather board. One striking peculiarity of the Opuntias fiber is that it is bleached without any preparation. When the pulp is removed, the remaining fiber is perfectly white, and ready for use without necessitating the usual process of bleaching. So the Opuntia which develops its enormous weight or tonnage of forage and its abundant supply of food for man in the early stages of its growth, will subsequently, without relinquishing its original function, produce supplies of fiber that may be of value. The rapidity and growth of the plant would insure the production of such quantities of material as to give it a certain importance even if it could be grown only on arable lands; but the quantity is at best relatively small. That it can be grown also on the waste places is obviously an additional merit of the first grade.


Let us, then, in conclusion summarize briefly the qualities that give the new spineless Opuntias economic value. In so doing I may refer to two or three subordinate uses to which the plants have been put that have not been specifically mentioned in the preceding studies. Here is the list: First: The new spineless Opuntias supply abundant quantities of fresh fruit that is unique in form and color, of superior flavor, of sure crop, and of good shipping quality. Delicious jams, jellies, and syrups may be made from the fruits; and its juices are used for coloring ices, jellies, and confectionery. Second: The slabs or so-called leaves of the plant supply an unprecedented amount of forage for stock of all kinds and for poultry. Third: The young slabs make excellent pickles, and are a good and wholesome food when fried like the eggplant. They are also boiled and used as greens, and may be prepared with sugar to produce a sweetmeat similar to preserved citron. Fourth: The leaves are extensively used in Mexico and elsewhere for poultices, and as a substitute for hot water bags-the thornless kind being naturally preferred! Fifth: The abundant plant juices contain a mucilaginous substance that is used to fix pigments, and which in time will be put to many other important uses. Sixth: The thorny varieties are used for hedges or fences, as well as for ornament, and even to protect the thornless ones. No animal of any kind will undertake to pass through one of these thorny hedges. In regions subject to the drifting of sand they serve an important purpose as barriers. Seventh: The fiber of the plant makes an admirable stock for the manufacture of paper, but not as yet in large quantities. Eighth: In general, the adaptability of the new Opuntias to the arid regions gives assurance that vast semi-arid regions of the globe will be made habitable and productive, although hitherto they have produced scant if any vegetation of economic value. Without looking further, it must be clear that a plant having such qualities may be regarded as the most neglected of vegetable products. Owing to its spines, the cactus has been regarded as an enemy of man. Now that its spines are removed its good qualities will in due course be appreciated. Should their present promise be fulfilled, the giant spineless Opuntias may make vast areas that hitherto have been relatively sterile among the productive regions of the world. They may supply fodder for unlimited numbers of cattle, that will give cheaper food to the masses, and conspicuously decrease the cost of living. They may even avert famines in regions that have hitherto accepted the recurrence of starvation years as an inevitable visitation. And even should the future benefits that accrue from the new spineless Opuntias realize but a fraction of their present promise, these plants might still be entitled to a foremost place among the forms of vegetable life that have been introduced, or improved, for the service of man within the historical period.


Before taking leave of the spineless cactus, it may be of interest to make further inquiry as to the hereditary bearings of the condition of spinelessness. We have seen that the new spineless opuntias were developed by a long series of experiments in hybridizing and selection, in which use was made of individuals that showed a propensity to depart from the spine-bearing custom of their race. Among the seedlings of these plants, some were found to be much less spiney than others, and it was ultimately possible, by selecting among literal millions of specimens, to develop races absolutely devoid of spines and spicules, as we have seen. It would not have been unreasonable, perhaps, to expect that the spineless races thus developed would breed true to spinelessness; particularly when we recall that the thornless blackberry, if inbred, produces only thornless progeny. But if such an expectation were entertained, it would be doomed to disappointment, for the spineless cactus does not breed true. In point of fact, there may be found among the seedlings of a spineless variety plants that fairly bristle with spines, rivaling in this regard the best-protected of their wild ancestors. Obviously, then, the condition of spinelessness in the cactus has quite different relations in the scheme of heredity from the conditions that govern spinelessness in the blackberry. In the latter case, as we have seen, the spineless condition appears to be recessive, and the thornless individual is as free from tendency to produce thorns as if its entire coterie of ancestors had been perfectly smooth-stemmed. The individual spineless cactus, on the other hand, retains the factors for spines in its germ plasm, to make their influence tangibly felt in a large proportion of the offspring. Nevertheless, it does not appear that the condition of spininess acts as a simple Mendelian dominant. On the contrary, it appears that the hereditary conditions that govern the spiny condition in the cactus are very complex. The best interpretation would seem to be that there are multitudes of actors for spicules and spines, variously blended in the germ plasm of any given individual. The spiny condition, on the whole, tends to be dominant to the spineless condition, because the spines are a relatively late development in the history of the evolution of the cactus tribe. But doubtless the period in question was an exceedingly long one, covering many thousands of cactus generations, during which the plants were becoming better and better protected; and each stage of such development may be thought of as having its hereditary factors in the germ plasm, capable of acting independently. Thus it is that in the same fraternity some seedlings are exceedingly spiny, while others have a comparatively small number of spines, and a few may be absolutely spineless. Thus, also, is explained the fact, to which attention has been called, that the plants that are altogether spineless may still be provided with minute spicules. Such minute spicules were, perhaps, the first defensive mechanism to be developed in the evolution of the cactus tribe, and they have back of them such numberless generations of heredity that they hold their own with exceptional persistency. In dealing with the spines and spicules of the cactus, then, we must consider that we have to do not with a single hereditary factor or two, but with a multitude of factors. Now our earlier studies have taught us that where several or many hereditary factors are in question, the probability that they will all be combined in any given way in a single individual decreases at a geometrical ratio. We found, for example, that where ten hereditary factors were under consideration, the probability of their combination in a predicted manner was only one in something over a million. In the case of the cactus the factors for spininess doubtless number far more than ten; from which it follows that the probability that any given seedling will have germ plasm absolutely free from any of the factors for spininess is much less than one in a million. This explains why it was necessary, in our experiments at Santa Rosa, to plant the seeds by literal millions, and to select persistently among uncomputed multitudes of seedlings. Fortunately the spiny condition reveals itself almost from the outset, so that it was possible to weed out the vast majority of all the seedlings, retaining only, perhaps, a stray dozen or so from among the legions. As the experiment proceeded, however, it was gratifying to note that in succeeding generations there was an ever-increasing proportion of spineless seedlings. This suggests that some of the factors for spininess were being dropped out of the heredity of the selected plants. Obviously this seems to augur that should the experiment be carried forward through a sufficient number of generations, the time will probably come when all factors for spininess will have been eliminated from the germ plasm of the selected opuntias; in which case, they will then breed true to spinelessness from the seed. This prediction finds further warrant in the fact that the newest races of spineless opuntias show a far more pronounced abhorrence-if the phrase be permitted-of the spiny conditions than did the earlier ones. It was observed that the first spineless opuntias to be developed at Santa Rosa, although remaining perfectly smooth under ordinary conditions of cultivation, had, nevertheless, a tendency to revert to the spiny condition if placed under disadvantageous conditions-say in arid soils, unwatered and uncultivated; a state comparable to that of the wild spiny progenitors. This tendency to reversion is in itself highly interesting from the standpoint of the student of heredity; being comparable, perhaps, to the observed tendency of some plants, on rare occasions, to form what are termed bud sports. As a rule, plants grown from cuttings or roots or buds reproduce absolutely the characteristics of the parent form. We have seen this illustrated over and over in endless numbers of cases, from orchard fruits to shasta daisies. This rule holds true of the cactus, as has been pointed out in recent chapters. You may produce an entire field of spineless opuntias of any given type, as offshoots of a single slab. But of course no plant is free from the power of environment, and no one needs to be told that the choicest orchard fruits, for example, will fail signally to justify expectations based on observa-tions of their parent forms, unless they are given proper conditions of soil and cultivation. Cuttings or buds of the Baldwin apple, for example, will produce but perverted replicas of the original Baldwin if grown in an arid soil, deprived of moisture, and shaded by other trees. Under such conditions, the choicest varieties of apples tend to revert more or less to the primitive type of the wild ancestor of very remote generations. Similarly the spineless opuntia may tend to revert to the wild form if placed under primeval conditions. In a stony, arid soil, deprived of moisture, it may not only be stunted in growth, but it may show a propensity to revert to the spiny condition. Such, at any rate, was the case with the earliest spineless opuntias that were produced at Santa Rosa. As the experiment has gone forward, however, the condition of spininess has been more and more subordinated, as just related; the proof being not only that the individual plants are absolutely free from spines and spicules, but that more and more of their seedlings are found to be spineless. And this elimination of the hereditary factors for spininess is so profound and deep-seated that the newer or more recently developed varieties of spineless opuntias appear to have lost altogether the capacity to revert to the spiny condition. Even under the most adverse conditions of soil and climate, they remain absolutely smooth. One other step of progress, and, we may confidently predict, the factors for spininess will be so completely eliminated from the germ plasm, that the spineless opuntias will breed true from the seeds. Even then, it must not be expected that the seed-lings in any given case will reproduce all the good qualities of the parents; any more than the seedlings of cultivated varieties of apple or pear or peach will duplicate the qualities of their parents. We have seen that the seedlings of the thornless blackberry are not precisely like the parent form. But they all are thornless. Such will be the case, ultimately, with the spineless opuntias. And it must be obvious that when this condition is attained, the experiment of developing the opuntias in any direction will be greatly facilitated. With many varieties of spineless opuntias in hand, each one absolutely free from the tendency to revert to the spiny condition, we shall be able to carry forward experiments in crossbreeding and selection through which any desired quality may be accentuated and developed. At the present time, for example, the spineless opuntias are somewhat lacking in protein content. Their forage value is not quite what it would be if the protein content could be increased. And there is no reason to doubt that such increase may be possible, through selective breeding. Already the developed spineless opuntias exceed all other plants in their capacity to produce an enormous quantity of forage. Through selective breeding their pre-eminence may be still further advanced in that each individual slab may be given enhanced food value. And the quantities of other useful chemical substances in the cactus may similarly be increased in selective varieties.

-Heretofore the development of my cactus has been along the lines of spinelessness, size and productivity; the future will see a marked improvement in the percentage of its food constituents.

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