Popular Science Monthly/Volume 15/September 1879/The Vanilla-Plant
By J. POISSON,
ASSISTANT NATURALIST IN THE PARIS MUSEUM OF NATURAL HISTORY.
OF all orchids the vanilla is the one most widely known; its fruit is deservedly esteemed and is an important article of commerce. Its valuable properties long ago brought the vanilla into notice. The fruit appears to have been first introduced into Europe in the beginning of the sixteenth century. The living plant was imported into England, toward the end of the eighteenth century, by Miller; but we can not with certainty determine which one of the few species of vanilla now known was then introduced. Linné, however, gave the name Epidendrum vanilla to the plant which had come into his hands, and which is supposed to have been identical with that brought by Miller. Several years later Swartz, on attentively studying the flower of the vanilla, observed notable differences between it and the flower of the genus Epidendrum; he was thus led to constitute a new genus, and Epidendrum vanilla now became Vanilla aromatica. Later Greville brought from America some cuttings of a vanilla differing from Vanilla aromatica, especially in the size of the leaves; to this Andrews gave the name Vanilla planifolia. This plant was brought first to England, thence to the Museum at Paris in 1810, and lastly to Belgium; it is the species whose fruit possesses the strongest perfume.
The vanilla throve in greenhouses, but as it was sensitive to cold, and did not fructify, and its flowers possessed no ornamental interest, its culture was very limited. For a long time the only fruits which came to Europe were from Mexico, or the Gulf of Mexico—the only points where the plant was cultivated on a large scale, and where its fructification appeared to be insured. It remained for later experimenters to add to the interest attaching to this plant, while at the same time, in some degree, augmenting the resources of the colonies.
At this time the impression made by certain recent researches on fecundation in plants was still fresh, and the questions of hybridation and crossing were closely studied.
It has ever since been believed that the fecundation of the vanilla in Mexico and the neighboring countries, where that plant fructifies normally, was brought about by the agency of certain insects which hitherto do not appear ever to have been observed performing this function. The hypothesis is almost equivalent to a certainty, now that we know the habits of the Orchideæ, especially as regards reproduction.
The right of priority in discovering the artificial fecundation of the vanilla has been claimed for many countries. It belongs to England, say those who dwell on the other side of the Channel; but, if we are to believe the Belgians, the true discoverer was Charles Morren. Nevertheless it appears indisputable that Neumann, head-gardener at the Paris Museum of Natural History, was the first to obtain the results of this fructification in 1830. From a single stock Neumann produced, in that year, over two hundred vanilla fruits of excellent quality.
M. Delteil, pharmacist in the navy, in his interesting study of the vanilla ("Étude sur la Vanille," 1874), gives a list of the works which have been published concerning this plant, and treats of its culture in Réunion Island particularly. He states that in 1839 Perrottet, on his second voyage to Bourbon, made known to some of his friends among the planters the process adopted by Neumann; for, though the vanilla was cultivated as a curiosity, it did not bear fruit there any more than in Europe. Nothing appears to have come out of this suggestion; but the case was different with the discovery made about the same time by a young slave, Edmond Albius, in the service of M. Ferréol Beaumont-Bellier. Albius bad noticed bow his master, who had considerable acquaintance with natural history, used to produce hybrids by cross-fertilization of the various flowers in his garden. Having made like experiments himself, the young slave observed that, on touching with a spine of palm the flowers of the vanilla, two little yellow bodies contained within changed position, and that fructification resulted from the contact. A new branch of commerce was henceforth created, and vanilla-beans, previously very dear, were quickly much lowered in price.
The vanilla is a climbing plant with pulpy stem, but it can reach the tops of high trees. In our greenhouses it attains proportions sufficiently great to enable us to judge of its appearance. Its stem, which can be easily made to ramify, is from two to three centimetres in diameter. Its leaves are arranged in two rows, or are alternately distichous, as the botanists say. In size they vary from fifteen to twenty centimetres, and they are slightly twisted on their short petiole, so as to appear to be inserted obliquely. This torsion seems to be produced by the need for the leaf of having its upper face always turned toward the light.
Besides the roots at the base of the plant and fixed in the soil, a multitude of adventitious aërial roots start from the stem or the branches, after the plant has reached a certain size. These roots hang free so long as the stem rises vertically, but become fixed in the soil when the stem touches the ground. They start from the level of a leaf alongside of a tendril, with the aid of which the plant climbs trees.
The stem, which in the interval between two leaves takes a direction the reverse of that taken in the next interval—a zigzag—is charged with a thick vesicating juice, which on being applied to the skin produces a blister.
The flowers appear in clusters at the axils of the leaves, and are numerous; but care is taken to leave only a small number of them on the plant when it is desired to have fine fruit. These flowers last for only one day, and fructification, in order to be successful, should take place in the morning. The instrument used for this operation is a pointed piece of bamboo. A skilled man can fecundate as many as one thousand flowers in a morning. One month after fecundation the fruit has attained its full size, yet it has still to remain on the plant six or seven months more before it reaches perfect maturity.
The flowers of the vanilla have none of that richness of color so common among orchids. They are whitish or yellowish, according to the species to which they belong. Apart from those which are cultivated on account of the perfume of their fruit, the others possess only a purely botanical interest.
A physiological detail that is worthy of mention is the attraction of the stigmas of these flowers for the pollen offered to them. Neumann the younger had frequent occasion to notice this while experimeriting on the fecundation of the vanilla at the Museum; and in a prize essay by H. Baillon the same fact is confirmed. "When the sky was overcast," he writes, "and the temperature rather low, I had to penetrate into the stigmatic antrum, in order there to place the little pollen apparatus; but, after the sun had made pretty warm the greenhouse in which the plant was suspended, then, provided the contents of the anther were not firmly attached to the top of the pins on which they were borne, they would become detached from it on being brought within a certain distance from the stigma, and, being strongly attracted, would shoot like an arrow into the cavity." This curious observation appears to be without precedent save in this plant; it is certainly of a character to interest the physiologist.
Darwin has observed a strange movement of the pollinia in the flowers of Catasetum, which, under the influence of innervation, "were shot forth to the distance of two or three feet"; but here the phenomenon is purely mechanical.
The first travelers who observed the vanilla in the wild state have asserted that it grows in low, moist situations near the seacoast; but in later times it has been found in the forests, and is known to occur in divers parts in Central America.
The number of species of the vanilla-plant is not clearly determined. Of types cultivated in Mexico there are twelve, and of these five are reckoned as distinct species. One of these species, the Vanilla lec, embraces six varieties. Delteil gives a list of species cultivated in different countries; it is as follows: In Mexico, Vanilla sativa, V. silvestris, V. planifolia, and V. pompona; in Guiana, V. guianensis, with yellow flowers and large fruit; at Bahia, V. palmarum; in Brazil and Peru, Linné's V. aromatica, which possesses less fragrance than the others. In Réunion two sorts are cultivated, both of them apparently varieties of V. planifolia.
Under the title of vanillon is found in commerce a short, thick vanilla-pod, produced by V. pompona, the fruit of which is of far less value than that of the V. planifolia.
Now that the cultivation of vanilla is widely extended, the fine quality of beans can be had at from one hundred and eighty to two hundred and fifty francs per kilogramme. But when it is "frosted," i. e., covered with needles of vanillin, it may fetch a higher price. Vanillon is worth about one fourth as much as vanilla.
Vanilla plantations, to be profitable, require great and constant care. The plants are multiplied by cuttings. The cuttings should bear three or four leaves, and may be a metre or over in length. Rainy and hot seasons are chosen by preference for planting. The cuttings must be planted in rows apart, in a soil rich in vegetable molds fertilized with the decaying leaves and branches of plants, especially of the banana. Each cutting should have a prop, and the ground at its root is to be kept moist by a heap of stones around the stem.
The best practice in these plantations is to train the plants on espaliers reaching from one prop to another. Generally the props are themselves plant-cuttings, which bear leaves and so shelter the young plants from the excessive heat of the sun. In case the props are of dead timber, the shrubs which are to afford shade must be planted in the intervals between the vanilla-plants. In addition to these means of shelter the plantation must be surrounded with a hedge of shrubbery for the sake of breaking the force of the winds.
Experience has shown that a vanilla plantation should not be worked for over seven years; but in the mean time a new one is got in readiness, so that there may be no interruption.
The vanilla harvest in Réunion occurs from May to August; in Mexico it takes place in December. The fruits, improperly called pods, are best when they have had good exposure to the sun, are fully mature, but not open, and gathered in a hot, dry season.
The modes of preparation differ according to locality, but in general they may be classed under three heads. The oldest method is that of alternately exposing the fruits to the sun and then keeping them in shade till they are sufficiently dry. This is the practice in Mexico and Guiana, where vanilla of excellent quality is produced. Sometimes they are exposed to the action of artificial heat to hasten the drying. Another mode consists in employing boiling water, in which the fruit is dipped for a while, and then treated with sunlight and shade as above. Finally, the third method consists in employing an oven at the temperature of 50° to 75° Cent.; in this the beans are heated from twenty-four to thirty-six hours. Among the many processes, M. Delteil appears to give the preference to that in use in Réunion, i. e., that which employs boiling water, together with the subsequent treatment. Excellent results are also obtained by spreading the fruit on black cloths and exposing them to the heat of the sun.
Finally, the fruit is sent to the drying-room. Here it remains for about a month, being looked after from time to time. The vanilla is then packed in tin cases to prevent its becoming too dry, which would impair its value.
- Translated from "La Nature" by J. Fitzgerald, A.M.