Popular Science Monthly/Volume 56/April 1900/Genuine Starch Factories
|GENUINE STARCH FACTORIES.|
By BYRON D. HALSTED, Sc. D.,
MUCH in this world is neither upon first nor last analysis true to name. From the corner grocery we buy a pound of starch in a rectangular package highly decorated with lithograph and lettering, setting forth the excellences of the product. "superior to all others," and manufactured, with the utmost care, by Messrs. So-and-So. The fact is that the big seven-story establishment did not make a grain of the starch, and the best that can be claimed is a satisfactory method of bringing the product already formed into the present acceptable condition.
But it is not the purpose of this paper to decry the refineries, whether they be of starch, sugar, or this or that of a hundred natural products, but to direct attention to the source of that very common and, it may be safely said, indispensable substance known to the English-speaking people as starch.
It will be no new surprise to state, by way of introduction to the subject, that starch is the ordinary everyday product of ordinary everyday plants. So humble a vegetable as the potato has gained its way into all lands of the Fig. 1.—Starch Granules of the Potato. more civilized peoples almost solely because it has a habit of storing away, in large underground stems, a vast amount of starch. Let this provident tendency disappear in this plant for a single season, and the crop growers would discard it from their list of remunerative plants, while millions of people would turn with dismay to some other source of a daily supply of starch. What this change in the nature of a single kind of plant would mean to the human race words can not describe. If the famine in Ireland of 1845 and some later years, induced by a rot in the potato, is any index, the misery would be something worse than we should care to even dream of. When there is a shortage of starch in India, a distress follows that is felt through the bonds of sympathy, if in no other way, the whole world round. Let rice fail to mature its grain, Fig. 2.—Starch Granules of Corn. which means, in short, not to store its starch in available form for man, and the dependent race is brought to the ghostly condition of starvation and thrown upon the charity of those people whose starch is in their grain elevators, sacks, and barrels almost without number.
Starch, it would seem from this, is the prime food element of the human family, the chief factor in the upbuilding of a race, because a fundamental aliment of our bodies.
If the starch' factories do not make, in the true sense, the product of their mills, it may be to the point to consider how this all-important substance comes into existence. The organic chemist tells us that starch is a ternary compound, and this agrees closely with the definition laid down by the dictionaries, only they add that it is odorless, tasteless, and insoluble in water. It is one of the proximate principles of plants, and is stored in the form of granules wonderfully variable in size and shape, but each kind having a type that is adhered to with much regularity. For example, the ordinary potato (Solanum tuberosum L.) produces a starch granule that is characterized by a form resembling the shell of the oyster. Fig. 1 is from a camera drawing of a cell from the center of a potato, with portions of adjoining cells, all of which were packed full of starch, a few grains only being represented.
Starch is acted upon differently by reagents, one of the leading tests for it being a solution of iodine. A drop of a very weak solution will determine the presence of starch in a cuff or shirt front by leaving a blue spot or streak where the iodine has been applied. By means of this reagent the student of plant tissues is readily able to locate starch when present in any slice of tissue he may have made. He would, for example, find much more starch in the tuber of the potato than in any other portion of the plant, and there the grains will be found many times larger than in the stem or the cells of the green leaves. Of the relation of the starch in the leaves to that in the underground stem something may be said later in this paper.
In the corn plant the starch is stored chiefly in the grain, and not in the subterranean portions, as in the potato. The granules of the corn starch are much smaller than those of the potato, as indicated by Fig. 2, which is from a camera drawing of a cell from a grain of corn and made to the same scale as Fig. 1. The granules are oval and not much marked with striæ or lines, but chemically the substance is the same in both cases.
Another leading starch is that of wheat, the form of the grains of which is shown in Fig. 3. While somewhat larger than the corn-starch granules, they are not otherwise widely different.
One could scarcely overlook the starch produced by the rice plant, for it feeds more people than the potato, corn, or wheat. The relative size and form of the rice-starch granules are shown in
|Fig. 3.—Starch Granules of Wheat.||Fig. 4.—Starch Granules of Rice.|
Fig. 4. It is seen that the grains are not large, and with a strong tendency to break up into small angular pieces.
There are almost as many forms of starch as plants producing it, some of them being very odd in shape. Thus the tapioca starch has a characteristic form, as also the sago; but it is not the purpose here to more than call attention to the form in which the substance under consideration is laid down in plants. The student of food adulterations is an expert in the detection of starches, and, with his microscope and skill, is able to decide how much of one kind of starch and how much of another is offered in the product under examination. It is a matter of congratulation that Nature has set herself so strongly against fraud in food stuffs as to record the origin of each grain of starch in the grain itself.
And that brings us to a consideration of that origin. We must accord to plants the exalted prerogative of being the exclusive and universal starch-formers in the world. Whether we note the growth of the potato tubers or the plumping out of the grains of corn, wheat, or rice, the same fact remains that storehouses are being filled with the same organic compound. There must be many preliminary steps before this process of storing is complete, and for these we need to seek elsewhere in the growing plant.
Even the most careless observer can not but be at home with the fact that the whole port and bearing of ordinary plants is for sun exposure. They rise from the ground as closely placed stems of grass or less neighborly orchard or forest trees, and hang out their leaves to catch the sun. The economy of substance is so well studied that there is a very large exposure at a minimum of expenditure of tissue. In short, the leaves are the organs for association with the sunlight. They reach toward the sun where light is scanty, as in the window, and even turn their faces to the orb of day, shifting the position hour by hour from sunrise to nightfall. The rapidity with which we come to the fundamental fact that leaves are for the sun almost surprises one. The purpose is as easily inferred, but the steps in the process are not so quickly taken. The facts that leaves are par excellence the starch factories and the sunlight the inobtrusive chemist are granted, and it remains only to show something of the steps of proof that science may have discovered.
We need, therefore, to consider starch from the standpoint of its composition, and upon this the chemists are fairly well agreed. It consists of three elements, with their atoms so arranged that the molecule of starch has the composition of six parts of carbon, ten of hydrogen, and five of oxygen, or, to express the formula in terse chemical terms, it stands C₆10₁₀O₅. If we can account for the bringing of these atoms together in the production of a single molecule of starch the laboratory has been explored and the secret is ours, even if we can not put it to practical use in our so-called "starch factories."
The independent plant, beyond serious question, gets its food from outside itself. There are two sources for these substances—namely, the soil-water bathing the absorbing roots, and the atmosphere, with which the aërial branches and their leaves are constantly surrounded. From the soil come the water and all the salts, ash constituents, and the like that may be dissolved therein, while the gases of the atmosphere bring, among its chief contributions, a constant and, in an always exceedingly diluted form, the carbon dioxide, or, sometimes called, the carbonic-acid gas. This compound, familiar to us as a product of combustion, fermentation, and decay, is composed of carbon and oxygen, and has the symbol CO₂ associated with it by chemists.
In short, for the formation of our starch the water (H2O) from the soil and the CO2 of the atmosphere, when brought together, may be made to combine with the formation of starch. A single diagram, while not perhaps an absolute statement of fact, may serve to represent the final result:
|= C6H10O5 + 12O.|
In other words, the six molecules of carbon dioxide and five of water combine with the formation of one molecule of starch and the liberation of twelve atoms of oxygen.
This driving off of such a large amount of oxygen, entirely against the whole tendency of that element, it is assumed, is at the expenditure of much force. The only one adequate to this work is solar energy, and this is abundantly at hand. That we need not seek further for this power is proved by many and conclusive tests. Vegetable physiologists to-day are able not only to locate the sun as the chemist, that effects the changes necessary for the production
Fig. 5.—Diagrammatic View of the Process of Photo-Synthesis.
of starch, but can show in what cells and portions of those cells the forces effect the synthesis. The chlorophyll granules in the living cell are the microscopic laboratories in which a silent chemist, powerful beyond all measurements, builds out of inorganic materials the food substance of the whole world of animals and plants. Fig. 5 is an attempt to present the above statements as to photo-synthesis in plants in such a form that it may appeal to the eye of the reader. A bit of maple twig is shown with one leaf in position. Passing up the stem in the young wood is Fig. 6.—Portion of Leaf Magnified, Illustrating Photo-Synthesis. the crude sap from the soil to the leaf. There is a downward flow of elaborated sap in the inner bark also represented. Solar energy is indicated by the wave lines as playing upon the upper side of the leaf, while the direction of the carbon dioxide is shown by the dotted lines entering from both above and below the leaf. Water of transporation is indicated as being given off, and upon a dry, hot day this is considerable, which, as it vaporizes in the tissue, tends to keep the latter cool. Lastly, with the formation of starch there is the escape of oxygen set free from the broken molecule of carbon dioxide or water or both in the formation of the starch.
Fig. 6 is a similar attempt to show the process of starch formation with the use of a portion of the leaf in section as it might appear under the microscope. The under portion of the leaf is seen as having openings in the skin, through which the gases and vapors pass, and the middle portion above shows the porous nature of that part that is most active in synthesis. The small oval bodies in all the cells, except those of the upper and under epidermis, represent the chlorophyll granules, the special seat of the special activities which result in the formation of the carbohydrate, familiar to all as starch. To the right is a leaf vein, through which the crude sap (c. s.) reaches the synthetic cells, and the elaborated sap (e. s.) descends to places where it is needed for growth or for storage.
With the above facts in mind, there is no wonder at the activity that may reside in a field of corn during a bright day in August. Starch is being made almost by the ton daily, and, if the conditions favor, the next month will find a rich harvest for the husbandman who has assisted in supplying the conditions for the desired output of the leading carbohydrate.
The genuine starch factories of the world are exceedingly small and equally numerous, and, with the sunlight as the active force, each green cell may contribute to the world's gain in the food substances that enable all creatures to live and move and enjoy a fairly comfortable existence.