All About Coffee Part 29

The hybrids are not only of value to the roaster, but also to the planter. They are vigorous trees, practically free from leaf disease; they stand drought well and also heavy rains; they are not particular in regard to shade and upkeep; never fail to give a fair and often a rather heavy crop. The fruit ripens all the year around, and does not fall so easily as in the case of _arabica_.

Among other hybrids (many were still under trial in 1919) may be mentioned: _Coffea excelsia x liberica_; _C. Abeokutae x liberica_; _C.

Dybowskii x excelsa_; _C. stenophylla x Abeokutae_; _C. congensis x Ugandae_; _C. Ugandae x congensis_; and _C. robusta x Maragogipe_.

There are many species of _Coffea_ that stand quite apart from the main groups, _arabica, robusta_ and _liberica_; but while some are of commercial value, most of them are interesting only from the scientific point of view. Among the latter may be mentioned: _Coffea bengalensis_, _C. Perieri_, _C. mauritiana_, _C. macrocarpa_, _C. madagascariensis_, and _C. schumanniana_.

[Ill.u.s.tration: COFFEA QUILLOU FLOWERS IN FULL BLOOM]

M. Teyssonnier, of the experimental garden at Camayenne, French Guinea, West Africa, has produced a promising species of coffee known as _affinis_. It is a hybrid of _C. stenophylla_ with a species of _liberica_.

Among other promising species recognized by Dr. Cramer are:

_Coffea congensis_, whose berry resembles that of _C. arabica_, when well prepared for the market being green or bluish; and

_Coffea congensis var. Chalotii_, probably a hybrid of _C. congensis_ with _C. canephora_.

_Caffein-free Coffee_

Certain trees growing wild in the Comoro Islands and Madagascar are known as caffein-free coffee trees. Just whether they are ent.i.tled to this cla.s.sification or not is a question. Some of the French and German investigators have reported coffee from these regions that was absolutely devoid of caffein. It was thought at first that they must represent an entirely new genus; but upon investigation, it was found that they belonged to the genus _Coffea_, to which all our common coffees belong. Professor Dubard, of the French National Museum and Colonial Garden, studied these trees botanically and cla.s.sified them as _C. Gallienii_, _C. Bonnieri_, _C. Mogeneti_, and _C. Augagneuri_. The beans of berries from these trees were a.n.a.lyzed by Professor Bertrand and p.r.o.nounced caffein-free; but Labroy, in writing of the same coffee, states that, while the bean is caffein-free, it contains a very bitter substance, cafamarine, which makes the infusion unfit for use. Dr. O.W.

Willc.o.x[98], in examining some specimens of wild coffee from Madagascar, found that the bean was not caffein-free; and though the caffein content was low, it was no lower than in some of the Porto Rican varieties.

Hartwich[99] reports that Hanausek found no caffein in _C. mauritiana_, _C. humboltiana_, _C. Gallienii_, _C. Bonnerii_, and _C. Mogeneti_.

_Fungoid Disease of Coffee_

The coffee tree, like every other living thing, has specific diseases and enemies, the most common of which are certain fungoid diseases where the mycelium of the fungus grows into the tissue and spots the leaves, eventually causing them to fall, thus robbing the plant of its only means of elaborating food. Its most deadly enemy in the insect world is a small insect of the lepidopterous variety, which is known as the coffee-leaf miner. It is closely related to the clothes moth and, like the moth, bores in its larval stage, feeding on the mesophyl of the leaves. This gives the leaves an appearance of being shriveled or dried by heat.

[Ill.u.s.tration: AN EIGHTEEN-MONTHS'-OLD COFFEA QUILLOU TREE IN BLOSSOM]

There are three princ.i.p.al diseases, due to fungi, from which the coffee plants suffer. The most common is known as the leaf-blight fungus, _Pellicularia tokeroga_, which is a slow-spreading disease, but one that causes great loss. Although the fungus does not produce spores, the leaves die and dry, and are blown away, carrying with them the dried mycelium of the fungus. This mycelium will start to grow as soon as it is supplied with a new moist coffee leaf to nourish it. The method of getting rid of this disease is to spray the trees in seasons of drought.

It was a fungoid disease known as the _Hemileia vastatrix_ that attacked Ceylon's coffee industry in 1869, and eventually destroyed it. It is a microscopic fungus whose spores, carried by the wind, adhere to and germinate upon the leaves of the coffee tree[100].

Another common disease is known as the root disease, which eventually kills the tree by girdling it below the soil. It spreads slowly, but seems to be favored by collections of decaying matter around the base of the tree. Sometimes the digging of ditches around the roots is sufficient to protect it. The other common disease is due to _Stilbium flavidum_, and is found only in regions of great humidity. It affects both the leaf and the fruit and is known as the spot of leaf and fruit.

[Ill.u.s.tration: COFFEA UGANDae BENT OVER BY A HEAVY CROP]

CHAPTER XVI

THE MICROSCOPY OF THE COFFEE FRUIT

_How the beans may be examined under the microscope, and what is revealed--Structure of the berry, the green, and the roasted bean--The coffee leaf disease under the microscope--Value of microscopic a.n.a.lysis in detecting adulteration_

The microscopy of coffee is, on the whole, more important to the planter than to the consumer and the dealer; while, on the other hand, the microscopy is of paramount importance to the consumer and the dealer as furnishing the best means of determining whether the product offered is adulterated or not. Also, from this standpoint, the microscopy of the plant is less important than that of the bean.

[Ill.u.s.tration: Fig. 331. Coffee (_Coffea arabica_). I--Cross-section of berry, natural size; _Pk_, outer pericarp; _Mk_, endocarp; _Ek_, spermoderm; _Sa_, hard endosperm; Sp, soft endosperm. II--Longitudinal section of berry, natural size; _Dis_, bordered disk; _Se_, remains of sepals; _Em_, embryo. III--Embryo, enlarged; _cot_, cotyledon; _rad_, radicle. (Tschirch and Oesterle.)]

_The Fruit and the Bean_

The fruit, as stated in chapter XV, consists of two parts, each one containing a single seed, or bean. These beans are flattened laterally, so as to fit together, except in the following instances: in the peaberry, where one of the ovules never develops, the single ovule, having no pressure upon it, is spherical; in the rare instances where three seeds are found, the grains are angular.

The coffee bean with which the consumer is familiar is only a small part of the fruit. The fruit, which is the size of a small cherry, has, like the cherry, an outer fleshy portion called the pericarp. Beneath this is a part like tissue paper, spoken of technically as the parchment, but known scientifically as the endocarp. Next in position to this, and covering the seed, is the so-called spermoderm, which means the seed skin, referred to in the trade as the silver skin. Small portions of this silver skin are always to be found in the cleft of the coffee bean.

The coffee bean is the embryo and its food supply; the embryo is that part of the seed which, when supplied with food and moisture, develops into a new plant. The embryo of the coffee is very minute (Fig. 331, II, _Em_)[101]; and the greater part of the seed is taken up by the food supply, consisting of hard and soft endosperm (Fig. 331, I and II, _Sa_, _Sp_). The minute embryo consists of two small thick leaves, the cotyledons (Fig. 331, III, _cot_), a short stem, invisible in the undissected embryo, and a small root, the radicle (Fig. 331, III, _rad_).

[Ill.u.s.tration: Fig. 332. Coffee. Cross section of bean showing folded endosperm with hard and soft tissues. x6. (Moeller)]

_Fruit Structure_

In order to examine the structure of these layers of the fruit under the microscope, it is necessary to use the pericarp dry, as it is not easily obtainable in its natural condition. If desired, an alcoholic specimen may be used, but it has been found that the dry method gives more satisfactory results. The dried pericarp is about 0.5 mm thick. Great difficulty is experienced in cutting microtome sections of pericarp when the specimen is embedded in paraffin, because the outer layers are soft and the endocarp is hard, and the two parts of the section separate at this point. To overcome this, the sections might also be embedded in celloidin. When the sections are satisfactory, they may be stained with any of the double stains ordinarily used in the study of plant histology.

[Ill.u.s.tration: Fig. 333. Coffee. Cross section of hull and bean.

Pericarp consists of: 1, epicarp; 2-3, layers of mesocarp, with 4, fibro-vascular bundle; 5, palisade layer; and 6, endocarp; _ss_, spermoderm, consists of 8, sclerenchyma, and 9, parenchyma; _End_, endosperm (Tschirch and Oesterle)]

A section cut crosswise through the entire fruit would present the appearance shown in Fig. 333. The cells of the epicarp are broad and polygonal, sometimes regularly four-sided, about 15-35 broad. At intervals along the surface of the epicarp are stomata, or breathing pores, surrounded by guard cells. The next layer of the pericarp is the mesocarp (Figs. 333, 334, 335), the cells of which are larger and more regular in outline than the epicarp. The cells of the mesocarp become as large as 100 broad, but in the inner parts of the layer they become very much flattened. Fibrovascular bundles are scattered through the compressed cells of the mesocarp. The cell walls are thick; and large, amorphous, brown ma.s.ses are found within the cell; occasionally, large crystals are found in the outer part of the layer. The fibro-vascular bundles consist mainly of bast and wood fibers and vessels. The bast fibers are as large as 1 mm long and 25 broad, with thick walls and very small _lumina_. Spiral and pitted vessels are also present.

[Ill.u.s.tration: Fig. 334. Coffee. Surface view of _ep_, epicarp, and _p_, outer parenchyma of mesocarp. x160. (Moeller)]

The layer next to this is a soft tissue, parenchyma (Fig. 333, 5; Fig.

334, _p_). The parenchyma, or palisade cells as they are called, is a thin-walled tissue in which the cells are elongated, from which fact they receive their name. The walls of these cells, though very thin, are mucilaginous, and capable of taking up large amounts of water. They stain well with the aniline stains.

The endocarp (Fig. 336) is closely connected with the palisade layer and has thin-walled cells that closely resemble, in all respects, the endocarp of the apple. The outer layer consists of thick-walled fibers, which are remarkably porous (Fig. 333, 6; Fig. 336) while the fibers of the inner layer are thin-walled and run in the transverse direction.

_The Bean Structure_

Spermoderm, or silver skin, is not difficult to secure for microscopic a.n.a.lysis; because shreds of it remain in the groove of the berry, and these shreds are ample for examination. It can readily be removed without tearing, if soaked in water for a few hours. The spermoderm is thin enough not to need sectioning. It consists of two elements--sclerenchyma and parenchyma cells. (Figs. 333, 337, _st_, _p_).

[Ill.u.s.tration: Fig. 335. Coffee. Elements of pericarp in surface view.

_p_, parenchyma; _bp_, parenchyma of fibro-vascular bundle; _b_, bast fiber; _sp_, spiral vessel. x160. (Moeller)]

Sclerenchyma forms an uninterrupted covering in the early stages of the seed; but as the seed develops, surrounding tissues grow more rapidly than the sclerenchyma, and the cells are pushed apart and scattered. The cells occurring in the cleft of the berry are straight, narrow, and long, becoming as long as 1 mm, and resemble bast fibers somewhat. On the surface of the berry, and sometimes in the cleft, there are found smaller, thicker cells, which are irregular in outline, club-shaped and vermiform types predominating.

Parenchyma cells form the remainder of the spermoderm; and these are partially obliterated, so that the structure is not easily seen, appearing almost like a solid membrane. The raphe runs through the parenchyma found in the cleft of the berry.

The endosperm (Figs. 333; 338) consist of small cells in the outer part, and large cells, frequently as thick as 100 , in the inner part. The cell walls are thickened and knotted. Certain of the inner cells have mucilaginous walls which when treated with water disappear, leaving only the middle lamellae, which gives the section a peculiar appearance. The cells contain no starch, the reserve food supply being stored cellulose, protein, and aleurone grains. Various investigators report the presence of sugar, tannin, iron, salts, and caffein.

The embryo (Fig. 331, III) may be obtained by soaking the bean in water for several hours, cutting through the cleft and carefully breaking apart the endosperm. If it is now soaked in diluted alkali, the embryo protrudes through the lower end of the endosperm. It is then cleared in alkali, or in chloral hydrate. The cotyledons shown have three pairs of veins, which are slightly netted. The radicle is blunt and is about 3/4 mm in length, while the cotyledons are 1/2 mm long.

[Ill.u.s.tration: Fig. 336. Coffee. Sclerenchyma fibers of endocarp. x160.

(Moeller)]