THE BOTANY OF THE COFFEE PLANT
Its complete classification by class, sub-class, order, family, genus, and species—How the Coffea arabica grows, flowers, and bears—Other species and hybrids described—Natural caffein-free coffee—Fungoid diseases of coffee
THE coffee tree, scientifically known as Coffea arabica, is native to Abyssinia and Ethiopia, but grows well in Java, Sumatra, and other islands of the Dutch East Indies; in India, Arabia, equatorial Africa, the islands of the Pacific, in Mexico, Central and South America, and the West Indies. The plant belongs to the large sub-kingdom of plants known scientifically as the Angiosperms, or Angiospermæ, which means that the plant reproduces by seeds which are enclosed in a box-like compartment, known as the ovary, at the base of the flower. The word Angiosperm is derived from two Greek words, sperma, a seed, and aggeion, pronounced angeion, a box, the box referred to being the ovary.
This large sub-kingdom is subdivided into two classes. The basis for this division is the number of leaves in the little plant which develops from the seed. The coffee plant, as it develops from the seed, has two little leaves, and therefore belongs to the class Dicotyledoneæ. This word dicotyledoneæ is made up of the two Greek words, di(s), two, and kotyledon, cavity or socket. It is not necessary to see the young plant that develops from the seed in order to know that it had two seed leaves; because the mature plant always shows certain characteristics that accompany this condition of the seed.
In every plant having two seed leaves, the mature leaves are netted-veined, which is a condition easily recognized even by the layman; also the parts of the flowers are in circles containing two or five parts, but never in threes or sixes. The stems of plants of this class always increase in thickness by means of a layer of cells known as a cambium, which is a tissue that continues to divide throughout its whole existence. The fact that this cambium divides as long as it lives, gives rise to a peculiar appearance in woody stems by which we can, on looking at the stem of a tree of this type when it has been sawed across, tell the age of the tree.
In the spring the cambium produces large open cells through which large quantities of sap can run; in the fall it produces very thick-walled cells, as there is not so much sap to be carried. Because these thin-walled open cells of one spring are next to the thick-walled cells of the last autumn, it is very easy to distinguish one year’s growth from the next; the marks so produced are called annual rings.
We have now classified coffee as far as the class; and so far we could go if we had only the leaves and stem of the coffee plant. In order to proceed farther, we must have the flowers of the plant, as botanical classification goes from this point on the basis of the flowers. The class Dicotyledoneæ is separated into sub-classes according to whether the flower’s corolla (the showy part of the flower which ordinarily gives it its color) is all in one piece, or is divided into a number of parts. The coffee flower is arranged with its corolla all in one piece, forming a tube-shaped arrangement, and accordingly the coffee plant[Pg 132] belongs to the sub-class Sympetalæ, orMetachlamydeæ, which means that its petals are united.
The next step in classification is to place the plant in the proper division under the sub-class, which is the order. Plants are separated into orders according to their varied characteristics. The coffee plant belongs to an order known as Rubiales. These orders are again divided into families. Coffee is placed in the family Rubiaceæ, or Madder Family, in which we find herbs, shrubs or trees, represented by a few American plants, such as bluets, or Quaker ladies, small blue spring flowers, common to open meadows in northern United States; and partridge berries (Mitchella repens).
The Madder Family has more foreign representatives than native genera, among which are Coffea, Cinchona, and Ipecacuanha (Uragoga), all of which are of economic importance. The members of this family are noted for their action on the nervous system. Coffee, as is well known, contains an active principle known as caffein which acts as a stimulant to the nervous system and in small quantities is very beneficial. Cinchona supplies us with quinine, while Ipecacuanha produces ipecac, which is an emetic and purgative.
The families are divided into smaller sections known as genera, and to the genus Coffea belongs the coffee plant. Under this genus Coffea are several sub-genera, and to the sub-genus Eucoffea belongs our common coffee, Coffea arabica. Coffea arabica is the original or common Java coffee of commerce. The term “common” coffee may seem unnecessary, but there are many other species of coffee besides arabica. These species have not been described very frequently; because their native haunts are the tropics, and the tropics do not always offer favorable conditions for the study of their plants.
All botanists do not agree in their classification of the species and varieties of the coffea genus. M.E. de Wildman, curator of the royal botanical gardens at Brussels, in his Les Plantes Tropicales de Grande Culture, says the systematic division of this interesting genus is far from finished; in fact, it may be said hardly to be begun.
Coffea arabica we know best because of the important rôle it plays in commerce.
|Complete Classification of Coffee|
|Sub-class||Sympetalæ or Metachlamydeæ|
The coffee plant most cultivated for its berries is, as already stated, Coffea arabica, which is found in tropical regions, although it can grow in temperate climates. Unlike most plants that grow best in the tropics, it can stand low temperatures. It requires shade when it grows in hot, low-lying districts; but when it grows on elevated land, it thrives without such protection. Freeman says there are about eight recognized species of coffea.
Coffea arabica is a shrub with evergreen leaves, and reaches a height of fourteen to twenty feet when fully grown. The shrub produces dimorphic branches, i.e., branches of two forms, known as uprights and laterals. When young, the plants have a main stem, the upright, which, however, eventually sends out side shoots, the laterals. The laterals may send out other laterals, known as secondary laterals; but no lateral can ever produce an upright. The laterals are produced in pairs and are opposite, the pairs being borne in whorls around the stem. The laterals are produced only while the joint of the upright, to which they are attached, is young; and if they are broken off at that point, the upright has no power to reproduce them. The upright can produce new uprights also; but if an upright is cut off, the laterals at that position tend to thicken up. This is very desirable, as the laterals produce the flowers, which seldom appear on the uprights. This fact is utilized in pruning the coffee tree, the uprights being cut back, the laterals then becoming more productive. Planters generally keep their trees pruned down to about six feet.
The leaves are lanceolate, or lance-shaped, being borne in pairs opposite each other. They are three to six inches in length, with an acuminate apex, somewhat attenuate at the base, with very short petioles which are united with the short interpetiolar stipules at the base. The coffee leaves are thin, but of firm texture, slightly coriaceous. They are very dark green on the upper surface, but much lighter underneath. The margin of the leaf is entire and wavy. In some tropical countries the natives brew a coffee tea from the leaves of the coffee tree.
The coffee flowers are small, white, and very fragrant, having a delicate characteristic odor. They are borne in the axils of the leaves in clusters, and several crops are produced in one season, depending on the conditions of heat and moisture that prevail in the particular season. The different blossomings are classed as main blossoming and smaller blossomings. In semi-dry high districts, as in Costa Rica or Guatemala, there is one blossoming season, about March, and flowers and fruit are not found together, as a rule, on the trees. But in lowland plantations where rain is perennial, blooming and fruiting continue practically all the year; and ripe fruits, green fruits, open flowers, and flower buds are to be found at the same time on the same branchlet, not mixed together, but in the order indicated.
The flowers are also tubular, the tube of the corolla dividing into five white segments. Dr. P.J.S. Cramer, chief of the division of plant breeding, Department of Agriculture, Netherlands India, says the number of petals is not at all constant, not even for flowers of the same tree. The corolla segments are about one-half inch in length, while the tube itself is about three-eighths of an inch long. The anthers of the stamens, which are five in number, protrude from the top of the corolla tube, together with the top of the two-cleft pistil. The calyx, which is so small as to escape notice unless one is aware of its existence, is annular, with small, tooth-like indentations.
While the usual color of the coffee flower is white, the fresh stamens and pistils may have a greenish tinge, and in some cultivated species the corolla is pale pink.
The size and condition of the flowers are entirely dependent on the weather. The flowers are sometimes very small, very fragrant, and very numerous; while at other times, when the weather is not hot and dry, they are very large, but not so numerous. Both sets of flowers mentioned above “set fruit,” as it is called; but at times, especially in a very dry season, they bear flowers that are few in number, small, and imperfectly formed, the petals frequently being green instead of white. These flowers do not set fruit. The flowers that open on a dry sunny day show a greater yield of fruit than those that open on a wet day, as the first mentioned have a better chance of being pollinated by the insects and the wind. The beauty of a coffee estate in flower is of a very fleeting character. One day it is a snowy expanse of fragrant white blossoms for miles and miles, as far as the eye can see, and two days later it reminds one of the lines from Villon’s Des Dames du Temps Jadis.
Where are the snows of yesterday?
The winter winds have blown them all away.
But here, the winter winds are not to blame: the soft, gentle breezes of the perpetual summer have wrought the havoc, leaving, however, a not unpleasing picture of dark, cool, mossy green foliage.
The flowers are beautiful, but the eye of the planter sees in them not alone beauty and fragrance. He looks far beyond, and in his mind’s eye he sees bags and bags[Pg 136] of green coffee, representing to him the goal and reward of all his toil. After the flowers droop, there appear what are commercially known as the coffee berries. Botanically speaking, “berry” is a misnomer. These little fruits are not berries, such as are well represented by the grape; but are drupes, which are better exemplified by the cherry and the peach. In the course of six or seven months, these coffee drupes develop into little red balls about the size of an ordinary cherry; but, instead of being round, they are somewhat ellipsoidal, having at the outer end a small umbilicus. The drupe of the coffee usually has two locules, each containing a little “stone” (the seed and its parchment covering) from which the coffee bean (seed) is obtained. Some few drupes contain three, while others, at the outer ends of the branches, contain only one round bean, known as the peaberry. The number of pickings corresponds to the different blossomings in the same season; and one tree of the species arabica may yield from one to twelve pounds a year.
In countries like India and Africa, the birds and monkeys eat the ripe coffee berries. The so-called “monkey coffee” of India, according to Arnold, is the undigested coffee beans passed through the alimentary canal of the animal.
The pulp surrounding the coffee beans is at present of no commercial importance. Although efforts have been made at various times by natives to use it as a food, its flavor has not gained any great popularity, and the birds are permitted a monopoly of the pulp as a food. From the human standpoint the pulp, or sarcocarp, as it is scientifically called, is rather an annoyance, as it must be removed in order to procure the beans. This is done in one of two ways. The first is known as the dry method, in which the entire fruit is allowed to dry, and is then cracked open. The second way is called the wet method; the sarcocarp is removed by machine, and two wet, slimy seed packets are obtained. These packets, which look for all the world like seeds, are allowed to dry in such a way that fermentation takes place. This rids them of all the slime; and, after they are thoroughly dry, the endocarp, the so-called parchment covering, is easily cracked open and removed. At the same time that the parchment is removed, a thin silvery membrane, the silver skin, beneath the parchment, comes off, too. There are always small fragments of this silver skin to be found in the groove of the coffee bean contained within the parchment packet.
We have said that the coffee tree yields from one to twelve pounds a year, but of course this varies with the individual tree and also with the region. In some countries the whole year’s yield is less than 200 pounds per acre, while there is on record a patch in Brazil which yields about seventeen pounds to the tree, bringing the yield per acre much higher.
The beans do not retain their vitality for planting for any considerable length of time; and, if they are thoroughly dried, or are kept for longer than three or four months, they are useless for that purpose. It takes the seed about six weeks to germinate and to appear above ground. Trees raised from seed begin to blossom in about three years; but a good crop can not be expected of them for the first five or six years. Their usefulness, save in exceptional cases, is ended in about thirty years.
The coffee tree can be propagated in a way other than by seeds. The upright branches can be used as slips, which, after taking root, will produce seed-bearing laterals. The laterals themselves can not be used as slips. In Central America the natives sometimes use coffee uprights for fences and it is no uncommon sight to see the fence posts “growing.”
The wood of the coffee tree is used also for cabinet work, as it is much stronger than many of the native woods, weighing about forty-three pounds to the cubic foot, having a crushing strength of 5,800 pounds per square inch, and a breaking strength of 10,900 pounds per square inch.
The propagation of the coffee plant by cutting has two distinct advantages over propagation by seed, in that it spares the expense of seed production, which is enormous, and it gives also a method of hybridization, which, if used, might lead not only to very interesting but also to very profitable results.
The hybridization of the coffee plant was taken up in a thoroughly scientific manner by the Dutch government at the experimental garden established at Bangelan, Java, in 1900. In his studies, twelve varieties of Coffea arabicaare recognized by Dr. P.J.S. Cramer, namely:
Laurina, a hybrid of Coffea arabica with C. mauritiana, having small narrow leaves, stiff, dense branches, young leaves almost white, berry long and narrow, and beans narrow and oblong.
Murta, having small leaves, dense branches, beans as in the typical Coffea arabica, and the plant able to stand bitter cold.
Menosperma, a distinct type, with narrow leaves and bent-down branches resembling a willow, the berries seldom containing more than one seed.
Mokka (Coffea Mokkæ), having small leaves, dense foliage, small round berries, small round beans resembling split peas, and possessed of a stronger flavor than Coffea arabica.
Purpurescens, a red-leaved variety, comparable with the red-leaved hazel and copper beech, a little less productive than the Coffea arabica.
Variegata, having variegated leaves striped and spotted with white.
Amarella, having yellow berries, comparable with the white-fruited variety of the strawberry, raspberry, etc.
Bullata, having broad, curled leaves; stiff, thick, fragile branches, and round, fleshy berries containing a high percentage of empty beans.
Angustifolia, a narrow-leaved variety, with berries somewhat more oblong and, like the foregoing, a poor producer.
Erecta, a variety that is sturdier than the typical arabica, better suited to windy places, and having a production as in the common arabica.
Maragogipe, a well-defined variety with light green leaves having colored edges: berries large, broad, sometimes narrower in the middle; a light bearer, the whole crop sometimes being reduced to a couple of berries per tree.
Columnaris, a vigorous variety, sometimes reaching a height of 25 feet, having leaves rounded at the base and rather broad, but a shy bearer, recommended for dry climates.
Coffea arabica has a formidable rival in the speciesstenophylla. The flavor of this variety is pronounced by some as surpassing that of arabica. The great disadvantage of this plant is the fact that it requires so long a time before a yield of any value can be secured. Although the time required for the maturing of the crop is so long, when once the plantation begins to yield, the crop is as large as that of Coffea arabica, and occasionally somewhat larger. The leaves are smaller than any of the species described, and the flowers bear their parts in numbers varying from six to nine. The tree is a native of Sierra Leone, where it grows wild.
The bean of Coffea arabica, although the principal bean used in commerce, is not the only one; and it may not be out of place here to describe briefly some of the other varieties that are produced commercially. Coffea liberica is one of these plants. The quality of the beverage made from its berries is inferior to that of Coffea arabica, but the plant itself offers distinct advantages in its hardy growing qualities. This makes it attractive for hybridization.
The Coffea liberica tree is much larger and sturdier than the Coffea arabica, and in its native haunts it reaches a height of 30 feet. It will grow in a much more torrid climate and can stand exposure to strong sunlight. The leaves are about twice as long as those of arabica, being six to twelve inches in length, and are very thick, tough, and leathery. The apex of the leaf is acute. The flowers are larger than those of arabica, and are borne in dense clusters. At any time during the season, the same tree may bear flowers, white or pinkish, and fragrant, or even green, together with fruits, some green, some ripe and of a brilliant red. The corolla has been known to have seven segments, though as a rule it has five. The fruits are large, round, and dull red; the pulps are not juicy, and are somewhat bitter. Unlike Coffea arabica, the ripened drupes do not fall from the trees, and so the picking can be delayed at the planter’s convenience.
A. Coffea arabica, R. Coffea robusta, L. Coffea liberica
Among the allied Liberian species Dr. Cramer recognizes:
Abeokutæ, having small leaves of a bright green, flower buds often pink just before opening (in Liberian coffee never), fruit smaller with sharply striped red and yellow shiny skin, and producing somewhat smaller beans than Liberian coffee, but beans whose flavor and taste are praised by brokers;
Dewevrei, having curled edged leaves, stiff branches, thick-skinned berries, sometimes pink flowers, beans generally smaller than in C. liberica, but of little interest to the trade;
Arnoldiana, a species near to Coffea Abeokutæ having darker foliage and the even colored small berries;
Laurentii Gillet, a species not to be confused with the C. Laurentii belonging to the robusta coffee, but standing near to C. liberica, characterized by oblong rather than thin-skinned berries;
Excelsa, a vigorous, disease-resisting species discovered in 1905 by Aug. Chevalier in West Africa, in the region of the Chari River, not far from Lake Tchad. The broad, dark-green leaves have an under side of light green with a bluish tinge; the flowers are large and white, borne in axillary clusters of one to five; the berries are short and broad, in color crimson, the bean smaller than robusta, very like Mocha, but in color a bright yellow likeliberica. The caffein content of the coffee is high, and the aroma is very pronounced;
Dybowskii, another disease-resisting variety similar to excelsa, but having different leaf and fruit characteristics;
Lamboray, having bent gutter-like leaves, and soft-skinned, oblong fruit;
Wanni Rukula, having large leaves, a vigorous growth, and small berries;
Coffea aruwimensis, being a mixture of different types.
The last three types were received by Dr. Cramer at Bangelan from Frère Gillet in the Belgian Congo, and were still under trial in Java in 1919.
Emil Laurent, in 1898, discovered a species of coffee growing wild in Congo. This was taken up by a horticultural firm of Brussels, and cultivated for the market. This firm gave to the coffee the name Coffea robusta, although it had already been given the name of the discoverer, being known as Coffea Laurentii. The plant differs widely from both arabica and liberica, being considerably larger than either. The tree is umbrella-shaped, due to the fact that its branches are very long and bend toward the ground.
The leaves of robusta are much thinner than those of liberica, though not as thin as those of arabica. The tree, as a whole, is a very hardy variety and even bears blossoms when it is less than a year old. It blossoms throughout the entire year, the flowers having six-parted corollas. The drupes are smaller than those of liberica; but are much thinner skinned, so that the coffee bean is actually not any smaller. The drupes mature in ten months. Although the plants bear as early as the first year, the yield for the first two years is of no account; but by the fourth year the crop is large.
Arno Viehoever, pharmacognosist in charge of the pharmacognosy laboratory of the Bureau of Chemistry, United States Department of Agriculture, has recently announced findings confirming Hartwich which appear to permit of differentiation between robusta, arabica, and liberica. These are mainly the peculiar folding of the endosperm, showing quite generally a distinct hook in the case of the robusta coffee bean. The size of the embryo, and especially the relation of the rootlet to hypercotyl, will be found useful in the differentiation of the species Coffea arabica, liberica, and robusta (see cut, page 142).
Viehoever and Lepper carried on a series of cup tests of robusta, the results as to taste and flavor being distinctly favorable. They summarized their studies and tests as follows:
The time when coffee could be limited to beans obtained from plants of Coffea arabica and Coffea liberica has passed. Other species, with qualities which make them desirable, even in preference to the well reputed named ones, have been discovered and cultivated. Among them, the species or group of Coffea robusta has attained a great economic significance, and is grown in increasing amounts. While it has, as reports seem to indicate, not as yet been possible to obtain a strain that would be as desirable in flavor as the old “standard” Coffea arabica, well known as Java or “Fancy Java” coffee, its merits have been established.
The botanical origin is not quite cleared up, and the classification of the varieties belonging to the robusta group deserves further study. Anatomical means of differentiating robusta coffee from other species or groups, may be applied as distinctly helpful….
As is usual in most of the coffee species, caffein is present. The amount appears to be, on an average, somewhat larger (even exceeding 2.0 percent) than in the South American coffee species. In no instance, however, did the amount exceed the maximum limits observed in coffee in general….
Due to its rapid growth, early and prolific yield, resistance to coffee blight, and many other desirable qualities, Coffea robusta has established “its own”. In the writers’ judgment, robusta coffee deserves consideration and recognition.
Among the robusta varieties, Coffea canephora is a distinct species, well characterized by growth, leaves, and berries. The branches are slender and thinner thanrobusta; the leaves are dark green and narrower; the flowers are often tinged with red; the unripe berries are purple, the ripe berries bright red and oblong. The produce is like robusta, only the shape of the bean, somewhat narrower and more oblong, makes it look more attractive. Coffea canephora,[Pg 146] like C. robusta, seems better fitted to higher altitudes.
Other canephora varieties include:
Madagascar, having small, slightly striped, bright red berries and small round beans;
Quillouensis, having dark green foliage and reddish brown young leaves; and,
Stenophylla Paris, with purplish young berries.
These last two named were under test at the Bangelan gardens in 1919.
Among other allied robusta species are:
Ugandæ:, whose produce is said to possess a better flavor than robusta;
Bukobensis, different from Ugandæ in the color of its berries, which are a dark red; and
Quillou, having bright red fruit, a copper-colored silver skin, three pounds of fruit producing one pound of market coffee. Some people prefer Quillou to robustabecause of the difference in the taste of the roasted bean.
Some Interesting Hybrids
The most popular hybrid belongs to a crossing of liberica and arabica. Cramer states that the beans of this hybrid make an excellent coffee combining the strong taste of the liberica with the fine flavor of the old Government Java (arabica), adding:
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. Abeokutæ x liberica; C. Dybowskii x excelsa; C. stenophylla x Abeokutæ; C. congensis x Ugandæ; C. Ugandæ 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.
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.
Certain trees growing wild in the Comoro Islands and Madagascar are known as caffein-free coffee trees. Just whether they are entitled to this classification 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 classified them as C. Gallienii, C. Bonnieri, C. Mogeneti, and C. Augagneuri. The beans of berries from these trees were analyzed by Professor Bertrand and pronounced 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. Willcox, 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 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.
There are three principal diseases, due to fungi, from which the coffee plants[Pg 148] 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.
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.