It would be impossible to enumerate the plants which furnish starch in large proportion, but a few may be given as illustrative of the above positions. The chemical analysis of those proximate principles of plants which are mere combinations of water with carbon (hydro-carbonates or hydrates of carbon) has been already given, but must here be repeated:—
| 100 parts consist of | ||
| Water. | Carbon. | |
| Gum (pure gum-arabic) | 58.6 | 41.4 |
| Sugar (pure crystallized) | 57.15 | 42.85 |
| Starch | 56.00 | 44.00 |
| Lignin | 50.00 | 50.00 |
These are so many mutually convertible products, of which gum may be looked upon as the basis; indeed gum is that organizable product which exists most universally in the proper juices of plants. “There are some instances in which sugar appears to be the first organic compound formed by the combination of the external elements, as when abundantly existing in the ascending sap of trees—the maple, for example. Starch may be considered as little else than gum divided into minute portions, each of which is enclosed in a membraneous cell (and containing some incidental particles, which, when starch is burnt, leave about .23 per cent. of residuum, consisting entirely of phosphates); and, in this state, it appears to answer very important ends in the vegetable economy. It is remarked by Decandolle, that, ‘while gum itself may be considered the nutrient principle of vegetation, diffused freely through the structure of the plant, and constantly in action, starch is apparently the same substance, stored up in such a manner as not to be readily soluble in the circulating fluids,’ thus forming a reservoir of nutritious matter, which is to be consumed, like the fat of animals (which it closely resembles in structure), in supporting the plant at particular periods[H].”
This view explains the fact of starch being found accumulated in amazing quantity in some plants, more particularly at certain periods of their existence, as in the cases I am now to cite. The fertility of some palm-trees is very great, and to furnish nutriment to the flowers, fruit, and seeds, an enormous supply of starch is needed; accordingly, in these we find the stem a complete storehouse of this essential principle. Thus the several palms and palm-like plants, which yield sago, such as the sagus Rumphii, cycas circinalis, C. revoluta, corypha umbraculifera, caryota urens, and phœnix farinifera—trees which are mostly confined within the tropics, at the moment when the spadices or sheaths containing the bunches of flowers are visible but not unfolded, furnish an immense portion of the food of the natives. The sagus Rumphii, which abounds in the islands of the Indian Archipelago, and though one of the humblest of the palm tribe, seldom exceeding thirty feet in height, is yet, except the gomuto, the thickest and largest, alone yields a quantity of nutritious matter far exceeding that of all other cultivated plants, inasmuch as a tree in its fifteenth year produces 600 lbs. of sago, which word, in the language of the Papuas, signifies bread, being the staple food of the islanders. To obtain it, the tree must be cut down, and the stem divided into pieces, from which the flour is beaten and washed out[I]. After being cut down, the vegetative power still remains in the root, which again forms a trunk, and this proceeds through its different stages, until it is again subjected to the axe, and made to yield its alimentary contents for the service of man. Nor is the extraordinary productiveness of a single tree the only point worthy of notice, for, being endogenous plants, devoid of branches, an unusual number of them can grow in a small space. Mr. Craufurd calculates that an English acre could contain four hundred and thirty-five sago trees, which would yield one hundred and twenty thousand five hundred pounds avoirdupois of starch, being at the rate of more than eight thousand pounds yearly. Besides the farina or meal, every tree cut down furnishes, in its terminal bud, a luxury which is as much prized as that of the areca oleracea, or cabbage palm of the West Indies, and which is eaten either raw as a salad, or cooked. Further, the leaves afford so excellent a material for covering houses, that even in those hot and humid parts of the world, where decomposition goes on so rapidly, it does not require to be renewed oftener than once in seven years.
The Mauritia flexuosa, or fan palm of the Oronooco, is of still greater utility to the natives of South America. It is a social palm, abounding in the marshes, and having a geographical range of very vast extent. The whole northern portion of South America, east of the Cordilleras, appears to be possessed of this gorgeous palm; from the mouth of the Oronooco to the river Amazon, and through the whole of Guiana, through Surinam and the northern part of Brazil, and in very various places along the river Amazon, even to its source on the eastern declivity of the Cordilleras, this palm is found, constituting forests of greater or less extent. Its smooth grey stem rising often 100 feet, forms groups that, in the northern part of Brazil, resemble the pallisades of some gigantic fortress. The produce of these lofty cylinders is very great, not merely of sago, which is procured only when the process of flowering is about to occur, but many trees being cut down before this event, a juice is obtained from them, which forms, by fermentation, a sweet wine; while those that flower, after which no good sago can be got, furnish an extraordinary quantity of fruit, hanging in bunches many feet in length, which is as agreeable as ripe apples, the taste of which it resembles. The other products of this tree are numerous[J].
It would lead beyond just limits, were we to notice in detail, the plants which yield starch suitable for food, only after undergoing a process of art, by which an acrid principle is driven off, and a bland, wholesome substance remains behind. Such is the Janipha (or Jatropha) Manihot, which yields the Mandiocca, Tapioca, or Cassava, an article not only of great consumption in, but also of considerable export from, Brazil (see Spix and Martius’ Travels, and Lib. of Enter. Knowledge, Vegt. Sub. Food of Man, p. 152), which, when raw, is poisonous both to man and cattle, though it becomes safe and agreeable by the application of heat. So likewise the large tubers of several Arums, such as A. Macrorhizon, A. Colocasia, Caladium acre, and which are cultivated with great care in tropical and subtropical countries, particularly in the Sandwich and South Sea islands. All of these excite inflammation and swelling of the mouth and tongue, even to the danger of suffocation, but which are disarmed of their virulence, and converted into an article of daily consumption, by fire. Even yams and sweet potatoes, which are naturally mild, are less articles of consumption in the south sea islands, than the Tarro, as these tubers of the arums are designated.
I omit all other plants to fix attention on the potatoe, which is not only the source of the purest starch of all, but has many interesting points connected with its history and habitudes, peculiarly connected with my subject. No plant has contributed more to banish those famines which were formerly of so frequent occurrence in Europe, and all the dire train of suffering and disease consequent upon them. Yet did it, in many instances, require royal edicts to induce some nations to cultivate what is now regarded as one of the prime blessings of Providence, from nearly one end of the earth to the other; the potatoe being raised from Hammerfest, in Lapland, lat. 71° north, through all Europe, the plains of India, in China, Japan, the south-sea islands, New Holland, even to New Zealand. What renders it so peculiarly valuable is, that in the seasons when the corn crop fails, that of potatoes is generally more abundant; thus furnishing a substitute for the other, which proves defective from atmospheric conditions, which have little influence over the potatoe, placed as it is underground, and secure against extremes of temperature. The potatoe is not a root, as commonly supposed, but an underground collection of buds, having a quantity of starch accumulated around them, for their nourishment when they begin to grow. The quantity of starch varies greatly with the kind of potatoe cultivated, the mode of cultivation, the time of setting, and above all, with the season of the year when the analysis is made. Potatoes in general, afford from one-fifth to one-seventh their weight of dry starch[K]; besides some other nutritive materials. The quantity of starch seems to be at its maximum in the winter months; as 100 pounds of potatoes yield in August about 10 lbs., in October nearly 15 lbs., in November to March 17 lbs., in April 13¾ lbs., and in May 10 lbs. Nor is the quantity of starch alone diminished in spring, but the nitrogen which belongs to some of the other nutritive principles, likewise suffers a deduction; as fresh, not dried potatoes, contain 0.0037 per cent. of azote, while potatoes ten months old contain only 0.0028, causing a sensible difference in their power of imparting nourishment. The starch is withdrawn from the tubers of the potatoe, precisely in the same way that it is transferred from the root, stem, or seeds of other plants, for the service of the young shoot; but the mode in which it is accomplished is but of recent discovery, and constitutes one of the most beautiful instances of design which the whole vegetable kingdom can unfold; “that man’s scepticism must be incurable who does not perceive, and acknowledge, that the means now to be detailed were created for the express accomplishment of the ends[L].”
Starch has been described above as consisting of a multitude of little cells or vesicles, having an envelope, insoluble in water, formed of a kind of organized membrane, and containing within it a substance which is soluble in water, termed amidin. This soluble material is the nutritive element on which the young shoot, proceeding from every eye or bud of the potatoes, is to subsist, till it has developed roots, and unfolded its leaves to prepare additional alimentary substance. But if this soluble material be enclosed in an insoluble membrane, how are the contents to be made available for the growth of the plant? It is true, indeed, that water of the temperature of 160° Fahr. can rupture this tegument, as occurs in the process of boiling potatoes; but the water diffused through the earth in the neighbourhood of the growing tuber, never reaches such a height. How then is the difficulty obviated? This is effected by a secretion called diastase which is found in the tubers in the immediate vicinity of the eyes or buds. “It is stored up in that situation for the purpose of being conveyed, by the vessels connected with the bud, into the substance of the tuber, when the demand for nutrition is occasioned by the development of the shoot. It is probable that the secretion of diastase takes place in every instance in which starch previously deposited is to be re-absorbed[M].” It is not to be found before grains or tubers begin to sprout, yet, “such is its energy, that one part of it is sufficient to render soluble the interior portion of two thousand parts of starch, and to convert it into sugar[N].” Strong as is the analogy between starch and gum, yet diastase does not convert gum into sugar; the one being as completely soluble as the other, its intervention is clearly unnecessary. Neither does it act on sugar. It is found, and exerts its powers, only where it is required. Nor does it come into play one moment before the necessity for it occurs. While the potatoe is in its state of winter repose, and no vegetative process going on, the elements of which the diastase is formed, are equally quiescent, but no sooner does the season recur when an augmented temperature rouses the slumbering energy of the tuber, than this potent principle exhibits its efficacy, and changes the insoluble starch into the nutritious sugar. Who, that can read, or reading reflect and ponder on these things, but must conclude that the laws which regulate the whole actions were impressed upon their subjects by a Creator infinite in design, in wisdom, and in power? If such insight into his doings are permitted to us now, what may we not hope for when we no longer “see as through a glass darkly[O]?”
The insolubility of the starch in cold water, affords a convenient means of separating the flour from the other materials, by which it may be abstracted from the tubers when in the greatest abundance, and be preserved unchanged for the use of man. This is done by simply rasping down the potatoes over a seirce, and passing a current of water over the raspings. The water passes through the seirce milky from the starch suspended in it. The starch is allowed to fall to the bottom, and is two or three times washed with pure water; it is then allowed to dry[P]. If this process be followed in the winter months, when the quantity of starch is greatest, the result is, a sixth portion of the weight of the potatoes employed, in a condition fit not only for immediate use, but capable of preservation for years. “To those who live solely, or even principally, on potatoes, it must be of immense importance to have the nutritious part preserved when in its greatest perfection, instead of leaving it exposed to injury, decomposition, or decay[Q].”
It is unnecessary to enlarge upon the sources of starch and its obvious utility to mankind. Previous to its being consumed by the plant in which it is amassed, it is by various means, but chiefly by diastase, transformed into sugar. Following this natural transition, I shall next consider sugar as an article of diet. In temperate climates, sugar is regarded as a luxury, one indeed which is nearly indispensable, but in tropical countries it is a universal article of subsistence, partly as real sugar, and partly, and more generally, as it occurs in the cane. It is inconceivable what enormous quantities of the sugar-cane is consumed in this way; vast ship-loads arrive daily in the market at Manilla, and in Rio Janiero; in the Sandwich Islands and other places, every child is seen going about with a portion of sugar-cane in the hand. It has been called “the most perfect alimentary substance in nature,” and the results, in the appearance of the negroes, during the cane-harvest, notwithstanding the increased severe toils of that season, seem to confirm the statement. They almost invariably become plump, and sleek, and scarcely take any other food while the harvest lasts; even the sickly revive, and often recover their health.