Rensselaer Union, Volume 7, Number 3, Rensselaer, Jasper County, 8 October 1874 — What Makes the Apples Rot? [ARTICLE]

What Makes the Apples Rot?

Our. worst enemies are the smallest. All the ravenous beasts in the world, mad dogs included, probably destroy Tower human lives than are destroyed in this city alone by the ravages of those minute but virulent organisms of the genus micrococcus to which we owe smallpox, diphtheria, and some other malignant diseases. Similarly, the thousand sturdy weeds which annoy the fanner, the caterpillars and grasshoppers which occasionally de%-our his crops, are relatively innocent and harmless compared with the numerous microscopic pests which rust his grain, rot his potatoes and fruit, and otherwise levy their burdensome taxes without making themselves visible. Just at this season, not the least interesting of these individually insignificant, collectively enormous, nuisances are two forms of fungus* growth- which have most to do with the untimely destruction of fruit —mucor miicedo and pencillium ylaucum. Our apples decay, not because it is their nature to, as. "Watts might say, but because it is the nature of something else to seize on them for subsistence, as we do, at the same time making of them a habitat , as we do not. Kept to themselves, apples and other fruit never rot; they simply lose their juicesdry evaporation, shrivel and become dry and hard, or, if kept from drying, remain substantially unchanged, as when securely canned. It is only when invaded by the organisms we have named that they lose color and quality, take on offensive tastes and odors, become covered with white or green mold —in short, develop rottenness and decay. Formerly this process was thought to be no other than a continuation op exaggeration of the natural process of ripening, the chemical changes which produce the odor and flavor of the ripened fruit simply going on to their legitimate though less delightful end. But this theory overlooked the very common and important facts that fruit may rot without ripening and that ripe fruit will not rot if properly protected. It was not until the microscope was brought to bear on the problem and the conditions of,decay were so convincingly demonstrated by Devaine that the real nature of the process became clear. Now we know that, so far fromi being the complement of growth, the antithesis of life, decay is in reality the taking on of a more rapid though specifically different growth. It is synonymous not with death but with intensely active life. In general structure the numerous microscopic fungi are very much alike, consisting mainly of a network of colorless cells and filaments called the mycelium. This: is the vegetable part. There is, besides, .a reproductive part in which -is produced the seed or “ spore,” the structure of which is different in the different genera. In the mucor each reproductive filament bears a globular swelling at its superior extremity in the interior of which the spores are developed. In the pencillium ylaucum the reproductive filament bears a tuft of from four to eight branches, which in turn produce upon their extremities a chaplet of small oval spores. It is called pencillium on account of this pencil-like tuft of its spore-bearing filaments, and ylaucum from their bluish-green tint. The mold so frequently seen in oranges is produced by this fungus. It is comparatively of slow growth and the alteration it produces in the properties of the fruit it lives in and upon is not so marked as that caused by the mucor. When a fruit is invaded by either of these fungi, the vegetative filaments send their branches among and around the fruit cells, and rapidly envelop them in a network of mycelium, absorbing the substance and juice of the fruit, and producing—the—chemical transformation characteristic of decay. All this goes on in the interior of the fruit, the fructification of the fungus taking place only on the surface, in contact with the atmosphere. For this reason fruit covered with a firm, fine «kin, like the apple, may be a mass of what we call corruption within—in other words, thoroughly decomposed by fungus growth—while * no visible mold—the fructifying part —appears on the surface. On the other hand, thin-skinned fruits like the strawberry, which are easily pierced by the reproductive filaments, are often covered with an abundant fructification in a very shprt time, for the fecundity of these microscopic fufigi is sometimes as marvelous as the rapidity of their growth. For example: A single zoospore of the peronspora infestans, which causes the potato rot, will envelop the cellular tissue of a potato leaf with mycelium filaments in twelve hours, and fructification will be completed in eighteen hours longer. One. square line of the under surface of a leaf, where the fructification naturally takes place, may bear as many as three thousand spores! Each spore supplies half a dozen zoospores, individually capable of originating a new mycelium. From one square line, therefore, there may come, in less than two days, nearly twenty thousand reproductive bodies, and a square inch may yield nearly three millions! No wonder the disease spreads rapidly. v In the case of fruit, decay may be originated in two ways, and two only: by direct contagion or by wind-wafted spores. With firm-skinned fruit like apples still another condition is essential, namely, a break in the skin of the fruit to allow the parasite to enter and take possession. In every case of decay in apples the center of disturbance wilt be found at a bruise, scratch, or puncture; and unless such a way be opened the apple may hang until it is dry as leather, or it may lie for weeks in direct Contact with rottenness, and remain perfectly sound. To this it may be objected that the constant presence of the fungus in decay is no proof that it is the cause of that condition; on the contrary, the breaking down of the fruit tissue by violence, and subsequent chemical action owing to access of air, may rather make the growth of the fungus 1 possible by preparing a suitable soil for its development. The objection has been met in the investigations 6T Davaine. The evidence that the

fungus precedes and causes the changes which we call decay is of the same character as that wluch" establishes the connection between a vaccine pustule and inoculation by vaccine virus. When soflnd fruit is' inoculated with the spores of pencillium decay begins at and spreads from the point of Apples similarly wounded, but not inoculated, remain the s&me.—Scientific Ahierican... ... ,