Popular Science Monthly/Volume 43/May 1893/Decay in the Apple Barrel
|DECAY IN THE APPLE BARREL.|
By BYRON D. HALSTED, Sc. D.,
FRUITS decay and everybody knows it, but how this rotting takes place is less evident. Grandfathers told our parents that it was due to the weather, and some of them may have held to the notion that the moon had a remarkable influence upon the keeping quality of various fruits. The perfection of the microscope and its more general use as an aid in seeing the minute things which surround us upon every side have led to a deeper comprehension of decays. It is the purpose of this article to show, if possible, some of the facts connected with the rotting of our apples, realizing that what holds true concerning one kind of fruit applies almost equally well to others.
Let us in the first place take a survey of the normal subject, or, in other words, of a healthy apple. It is made up of five seed cavities which occupy the central portion of the fruit and constitute the core. Outside of this is the edible portion called the flesh, consisting of cells of small size filled with liquid substances. A tough layer covers the outside, which is the skin, and bears the coloring substance that determines whether the apple is green, red, mottled, or striped. At one end of the fruit is the stem, or, as found in the barrel, this former means of attachment to the branch of the tree may have been broken away or pulled from the fruit — a matter of no small consideration when the question of decay is concerned. This end of the apple is known to the horticulturists as the "cavity," and varies greatly in different sorts, sometimes being deep and narrow as in the Winesap and Pearmain, and broad and shallow in the Greening and Peck's Pleasant.
The opposite end of the apple bears the name of "basin," and contains the remnants of the blossom — sometimes called the eye of the fruit. This part of the apple is likewise deep in some varieties, and shallow and open in others. This is the weakest point in the whole apple as concerns the question of the keeping quality of the fruit. If the basin is shallow and the canal to the core firmly closed, there is much less likelihood of the fruit decaying than when it is deep, and the evident opening connects the center of the fruit with the surface.
For its own protection the perfect apple has a continuous layer of skin over its whole surface. The stem has not been removed from its cavity, but remains of its full length, for there is a place naturally provided for its separation from the branch which bore it. Such an apple is the rare exception as found in the barrel. At the market or in the storeroom of the consumer,
|Fig. 1. — Apple Specks. (Magnified.)|
instead of being without blemish upon the surface, there are small specks as large as a pin-head, or smaller, which dot the skin in patches. A portion of the surface of an apple with these specks is shown three times magnified in Fig. 1. Sometimes one needs to look for a long time to find a fruit entirely free from these specks. Under the compound microscope these dots are resolved into a thin layer of interwoven threads, with their free ends radiating from a central point. This is one of the low forms of plant life belonging to the molds, and grows from microscopic cells called spores, which in the economy of the mold serves the purpose of seeds. These spores are produced in great abundance, and, being carried by the air, alight upon the fruit and there germinate and grow into a colony or speck which is all the time feeding upon the substance obtained from the skin of the apple.
The second defect in apples, as seen in the barrel, is the one known to fruit-dealers as the "scab." To the eye this is recognized by the rough-coated patches, often circular in outline, that are present upon the skin. There may be several of these spots, and, by their borders becoming confluent, one half or less of a fruit may be thus rough coated and more or less dwarfed, making the apple one-sided. This scab is due to a mold which, under the microscope, is as different in its real structure from the specks above mentioned as the two are unlike in general appearance. If it will add anything to the value of this popular article, the botanical name of the species of mold causing the apple scab may be given as Fusicladium dendriticum, Fl. It is as much a distinct kind of plant as the apple tree upon which it thrives. It is not confined to the fruit, but grows luxuriantly upon the foliage, causing it to become blotched with the brown patches and otherwise destroyed. The mold consists of fine, cobwebby threads, which penetrate the leaf and rob it of nourishment, and after a time form patches upon the surfaces, where innumerable spores of a dark color are produced.
The apples are first attacked by the scab fungus when they are quite small, probably while the tree is in blossom, or shortly after. At that time the surface of the young fruit is tender and has no well-developed skin, which, when the fruit nears maturity, might be so tough as to prevent the entrance of the scab mold. This, therefore, is a defect that does not come upon the fruit after harvest, and usually does not spread much after the apples are in the barrel.
The knowledge of the fact that the scab is due to a mold that begins to infest the fruit in early summer has led to experiments
Fig. 2. — Apple Scar.
in spraying the trees during the growing season with the Bordeaux mixture and other fungicides, with marked success in checking its ravages. Trees sprayed three or four times in May or June have borne abundant fruit comparatively free from scab, while unsprayed trees otherwise alike yielded a scant amount of distorted, scabby, withered apples. Fig. 2 shows an apple that is a fair illustration of the working of the scab fungus.
One of the most interesting things in connection with the study of the decays of apples is the relation which one mold bears to another. There are several very common kinds of molds. which grow nearly everywhere when circumstances favor them. Their spores seem to be almost omnipresent, but they do not possess the ability to penetrate tough substances, and the natural skin of the apple is usually a barrier they can not pass. Of all these molds the Penicillium glaucum, Lk,, or commonly known as the "blue mold," is the one that causes the greatest destruction in the storeroom. A large part of the rapid soft rot is due to the Penicillium.
In a few words let the work of the scab fungus be reviewed. As the name indicates, it causes a scab upon the surface, the
Fig. 3.—Apple Mold following Apple Scab.
naturally smooth, tough skin is roughened, and minute cracks are produced which in short replace the ordinary skin, impervious to the blue mold, with a disrupted coat that furnishes both a fine lodgment for the spores of the mold and the condition favorable for their germination and the further rapid growth of the mold. It is easy to conceive of the scab upon an apple being so slight and superficial as not to affect its real value, but the one defacement becomes the entrance of a decay germ, that in a few days reduces the whole apple to a noisome mass of rottenness resulting in a million spores or blue mold. To prevent the soft rot of the apple in midwinter in the barrel, the trees need to be sprayed in midsummer in the orchard, to check the development of the scab that would otherwise furnish the place of entrance of the blue mold. Fig. 3 shows an apple that, when harvested, had a number of rough circular patches due to the scab fungus. When the photograph was taken, each one of these spots was the seat of a rapid decay, due to the development upon them of the Penicillium, while all other portions of the fruit were in a normal condition,
There are many diseases due to those exceedingly minute germs so widely talked of nowadays — namely, the bacteria. They attack animals and induce fevers of many sorts, and man sinks before them with the dreaded cholera, consumption, etc. Plants have their enemies among these micro-organisms, and apples do not enjoy an immunity from them. The succulent substance of a ripe apple is a favorite food for the bacteria, the only check upon their abundant entrance being the tough skin. But there are too many weak places, and it is presumable that these germs when falling upon them are capable of beginning their course of rapid multiplication which, when unchecked, reduces the fruit to rottenness. In Fig. 4 is seen an apple under the apparently unbroken skin of which in several places were decaying spots with no signs of any other mischief-makers than the swarming millions
Fig. 4. — Apple Blotch.
of the micro-organisms. As soon as the skin becomes broken in any such places, the coarser decay germs enter and quickly the fruit is overrun with a motley vegetation of various molds.
If we look further among the decaying fruits, it will not be long usually before an apple is found that does not agree with any of the descriptions given above. Perhaps it is healthy in all parts save one, and that has no scab present. The blue mold is absent, the skin is unbroken except in a peculiar, almost regular manner. There is an evident central point where the fungus started, and, as it has spread, numerous pimples have formed just under the skin, and sometimes in eccentric circles. From these minute light-colored pimples spores ooze out and are ready to find their way to some other specimen. The affected portion of the apple has a bitter taste, and, on account of this, the term "bitter rot" has long been given to this form of decay. This
Fig. 5.—Apple Bitter Rot.
same fungus causes the rotting of the grapes, and, if all the facts were known, this Glœosporium fructigenum, Berk., might be definitely charged with a large percentage of the decay of other fruits. An apple badly affected with the bitter rot is shown in Fig. 5, but one regrets that many of the details are lost in the photo-engraving process by which the engraving was made.
This form of rot while it may be met with upon the tree or in the windfalls beneath it in late summer, is most abundant in the storeroom and is decidedly contagious—that is, an apple that is decaying with the bitter rot is able to communicate the decay to other fruits by means of the myriads of spores which are borne upon the surface of the ruptured pimples. These facts suggest the precaution of discarding any rotting fruits whenever found. There is little room for doubt that were the harvested fruits themselves sprayed with a fungicide, it would aid materially in preserving them. Thus, if a thin coating of the Bordeaux mixture was applied, the spores of bitter rot and other decay germs would not so readily germinate. But there is the objection of having the beauty of clean fruit lost under a film of fungicide that while not particularly poisonous is decidedly unpalatable, consisting of lime and sulphate of copper. A sensation was created in New York two years ago because grapes were thus marketed, and the same process for stored fruit is not here recommended, although its effectiveness as a preservative is granted.
A decay that might be mistaken for the last mentioned is caused by a fungus of a widely separated order. It is shown in Fig. 6. This might be called the black rot, as it has a strong tendency to turn the affected portions of a dark color. One of the characteristic features is the almost black pimples formed in considerable numbers beneath the skin, which they finally rupture and then discharge large numbers of dark-olive spores. This fungus
Fig. 6.—Apple Black Rot.
is a described species bearing the name Sphœropsis malorum, Pk. It may be seen in early apples before they begin to ripen, and the windfalls as they lie upon the ground become badly infested with the Sphœropsis. It is not confined to the apple, but thrives destructively upon quinces and pears as well. This decay in its habits of growth calls to mind the fact that the basin is the weakest point of fruits like the three above mentioned, for in most instances the black rot begins at the free end where the remnants of the flower may be still adhering, and very likely assist in the fungus gaining a foothold. This decay, like the bitter rot, is amenable to treatment, and therefore, in order to check their destructive work in the storeroom, the fungicide needs to be applied while the fruits are growing upon the trees. Thus the work of the prevention begins a long time previous to picking—while the barrel-staves are possibly still in the living forest tree. This reminds one of the time when the boy's education should begin as stated by Dr. Holmes, namely, with his grandfather when he was a small lad.
Up to this point remarks concerning the mechanical treatment of apples have been purposely withheld. There is no question about the importance of so far as possible preventing the bruising of the fruit. From what has been said in strong terms concerning the barrier of a tough skin which Nature has placed upon the apples, it goes without saying that this defense should not be ruthlessly broken down. It may be safely assumed that germs of decay are lurking almost everywhere, ready to come in contact with any substances. A bruise or cut in the skin is therefore even worse than a rough place caused by a scab fungus as a lodgment provided by the minute spores of various sorts. If the juice exudes, it at once furnishes the choicest of conditions for molds to grow. An apple bruised is a fruit for the decay of which germs are specially invited, and when such a specimen is placed in the midst of other fruit it soon becomes a point of infection for its neighbors on all sides. Seldom is a fully rotten apple found in a bin without several others near by it being more or less affected. A rotten apple is not its brother's keeper.
The surrounding conditions favor or retard the growth of the decay fungi. If the temperature is near freezing they are comparatively inactive, but when the room is warm and moist the fruit can not be expected to keep well. Cold storage naturally checks the decay. The ideal apple has no fungous defacements and no bruises. If it could be placed in a dry, cool room free from fungous germs it ought to keep indefinitely until chemical change ruins it as an article of food. But the facts in the case are far different from this ideal. The apple when gathered from the tree may have the germs of decay already within its tissue. They may have extended through the basin, become firmly located in the ragged remnants of the flower or by means of some insect or "worm" that has bit or burrowed the fruit. Its stem may have been broken close to the fruit or pulled out from it, or over the surface specks and scabs may have formed during the season of growth that have so destroyed the skin as to furnish a ready entrance for other more destructive germs. Bruises of the pulp and breaks in the skin expose the soft, highly decomposable flesh to the "seeds" of decay, and as one contemplates what an apple is made of and its many enemies, it seems almost a marvel that fruit keeps at all until it is cooked to kill the germs within it and then canned to prevent the entrance of those that are without. It is not designed that apples in their natural state should keep for long, and all attempts to preserve them in the fresh condition through the winter and far into the succeeding spring are a triumph against Nature only to he won by the person who is conversant with the methods of his microscopic opponents. The use of fungicides in the orchard while the fruit is growing will insure more and fairer specimens, thus filling a larger number of barrels with apples that are less subject to attack after harvest. This, with careful handling to avoid bruises when picked and housed, together with a dry storage room, should all bring a full reward. Fig. 7 shows an apple in the last stages of dissolution, overrun inside and out with a diminutive forest of fungi. It is the seed-time,
Fig. 7. — Apple Mold.
so to speak, with the host of species each vying with the others for the last particle of the apple, the seeds only being left behind ready to grow into trees when suitable circumstances obtain, provided the vital spark does not expire before the favoring condition arrive. The pulp that has been destroyed is largely man's product developed by him through long years of selection and culture, and for which the orchard is planted and preserved. Nature wants more apple seed; man desires more and better pulp. Nature claims that the pulp of the wild apple is only to secure the wider dissemination of the seed, and to the orchardist, middleman, and consumer she speaks in her emphatic way that "if you would exact of me extra-fine pulp, you must at the same time employ the best devices of your high civilization to preserve it from your omnipresent and active competitors, the insidious germs of decay."