THE Swedish botanist, Peter Kalm, a pupil of Linnaeus, who travelled in North America in 1748-9, has had the honor of giving name to one of the most elegant genera of flowering shrubs which our continent produces. The genus named Kalmia by Linnaeus, includes several species, of singular beauty, among which the Mountain laurel is much the largest and most elegant, as well as the one whose properties have received most attention. Its occurrence in the United States is very frequent, and its common appellations of course various. The names of Laurel, Lambkill, Ivy, Spoonwood, and Calico bush, it seems, are applied to it in various parts of the country. This shrub grows in the southern parts of New Hampshire, and is occasionally met with throughout Massachusetts. In the Middle States it becomes more frequent, and it is said to extend near to the southern limits of the Union. Michaux, in his account of the forest trees, states, that it is particularly abundant through the whole range of Allegany mountains, upon the borders and near the sources of rivers. It gradually diminishes however on both sides as these rivers approach to the sea, or to their confluence with the great western streams.
The botanical character of the genus consists in a five parted calyx, a hypocrateriform corolla, containing ten depressions in its border, in which the anthers are lodged; a capsule five celled.
The specific character is, that the leaves are scattered, petioled, oval and smooth; the corymbs terminal, viscid and pubescent.
Class Decandria, order Monogynia. Natural orders Bicornes, Linn. Rhododendra, Juss.
The height of the Kalmia latifolia is generally that of a shrub, sometimes however attaining to the altitude of a small tree. Its leaves are evergreen, coriaceous, very smooth, with the under side somewhat palest. Their form is oval, acute and entire; their insertion by scattered petioles, on the sides and extremities of the branches. The flowers vary from white to red; they grow in terminal corymbs, simple or compound with opposite branches, and made up of slender peduncles. These are invested with a glutinous pubescence, and supported at base by ovate, acuminate bractes. The calyx is small, five parted, persistent, with oval, acute segments. The corolla is monopetalous, with a cylindrical tube, a spreading disc, and an erect, five cleft margin. At the circumference of the disc on the inside, are ten depressions or pits, accompanied with corresponding prominences on the outside. In these depressions the anthers are found lodged at the time when the flower expands. The stamens originate from the base of the corolla, and bend outwardly, so as to lodge their anthers in the cells of the corolla. From this confinement they liberate themselves during the period of flowering and strike against the sides of the stigma. The germ is roundish, the style longer than the corolla and declined, the stigma obtuse. Capsule roundish, depressed, five celled and five valved, with numerous small seeds.
I have examined chemically the leaves of the Kalmia, gathered at the time the shrub was in fruit. The following constituent principles were found to exist in them.
1. Vegetable mucus. This exists in large quantities, and is dissolved in water both by infusion and decoction, rendering it extremely mucilaginous or ropy. When alcohol is added to this solution, the mucus separates in the form of a flocculent coagulum, which is tough and stringy, and on drying has a brownish colour. When chewed, it soon fills the mouth with mucilage.
Silicated potash rendered the upper stratum of the liquid dark and opaque, but without any precipitate like that which takes place in the mucilage of gum.
2. Tannin. This is readily thrown down from the decoction and tincture by gelatin. The sulphate of iron strikes with it a very black colour.
3. Resin. This also exists plentifully. It communicates to alcohol a reddish colour, and is instantly precipitated from it by water. When obtained pure, it is of a reddish cast, fusible, inflammable and moderately bitter.
I have not detected any extractive, properly so called, in these leaves. When the muriate of tin is added to the decoction, it separates a very copious yellow precipitate. This however is owing to the mucus. If alcohol be first added to the decoction, and the coagulum which it forms withdrawn; the fluid no longer gives a precipitate with muriate of tin, although it readily yields one to gelatin.
Distillation with water affords a mild fluid with little taste or odour.
The Kalmia latifolia, together with some other species of its genus, has long had the reputation, in various parts of the country, of being poisonous to certain domestic animals. Cateshy says of it, that "deer feed on its green leaves with impunity; yet when cattle and sheep, by severe winters deprived of better food, feed on the leaves of this plant, a great many of them die annually."
Kalm, the Swedish traveller, who gave name to this genus, says of Kalmia latifolia, "The leaves are poison to some animals, and food for others; experience has taught the people, that when sheep eat of these leaves, they either die immediately, or fall very sick, and recover with great difficulty. The young and more tender sheep are killed by a small portion, but the older ones can bear a stronger dose. Yet this food will likewise prove mortal to them, if they take too much of it. The same noxious eftect it shews in regard to calves which eat too much of the leaves; they either die, or do not recover easily. I can remember that in the year 1748 some calves ate of the leaves; they fell very sick, swelled, foamed at the mouth and could hardly stand; however, they were cured by giving them gunpowder and other medicines. The sheep are most exposed to be tempted with these leaves in winter, for after having been kept in stables for some months, they are greedy of all greens, especially if the snow still lies upon the ground, and therefore the green but poisonous leaves of the Kalmia are to them very tempting. Horses, oxen and cows, which have eaten them, have likewise been very ill after the meal, and though none of them ever died of eating these leaves, yet most people believed, that if they took too great a portion of them, death would certainly he the result." "On the other hand, the leaves of the Kalmia are the food of stags, when the snow covers the ground and hides all other provisions from them. Therefore, if they be shot in winter, their bowels are found filled with these leaves, and it is very extraordinary, that if those bowels are given to dogs, they become quite stupid, and, as it were, intoxicated, and often fall so sick, that they seem to be at the point of death; but the people who have eaten the venison have not felt the least indisposition."—Travels in North America, vol. i.
There is a common belief, that the flesh of the American Pheasant or Partridge is at certain times imbued with a poisonous quality. This circumstance has been attributed (I know not with what evidence) to their feeding in winter upon the buds of the Kalmia. Mr. Wilson, the ornithologist, informs us, that he has sometimes found the crops of these birds distended almost entirely with laurel buds; but that he has eaten freely of the flesh of these very birds, without any ill consequence whatever.
On the human system, the Kalmia has been also said to manifest a deleterious influence. The late Professor Barton has adduced some evidences of its noxious character. [Dr. Barton states, that a few drops of the tincture poured upon the body of a large and vigorous rattlesnake, killed the reptile in a very short time.] He states that the Indians make use of a decoction of the leaves to destroy themselves. In an Inaugural Dissertation on two species of Kalmia, the latifolia and angustifolia, by Dr. G. K. Thomas, we are told that the leaves of these shrubs possess a decidedly narcotic property. I have not recently seen Dr. Thomas' Dissertation, and therefore quote from memory and from extracts. From his experiments however it appeared, that a very small quantity was sufficient to produce sensible inconvenience. Thirty drops of a strong decoction, given six times a day, are said to have occasioned so much vertigo, as to render it necessary to diminish the frequency of its exhibition.
From my own experience, I am not disposed to think very highly of the narcotic power of the Kalmia. I have repeatedly chewed and swallowed a green leaf of the largest size, without perceiving the least effect in consequence. I have also seen the powder, freshly made from leaves recently dried, taken in doses of from ten to twenty grains, without any subsequent inconvenience or perceptible effect. The taste of these leaves is perfectly mild and mucilaginous, being less disagreeable than that of most of our common forest leaves.
I am inclined to believe that the noxious effect of the Kalmia upon young grazing animals may be in some measure attributed to its indigestible quality, owing to the quantity of resin contained in the leaves.
An ointment made of the powdered leaves has been recommended in tinea capitis and some other cutaneous affections. I have seen an eruption, very much resembling psora, removed by it.
The wood of the Kalmia is hard and dense, approaching in its character to that of box. It is much used for the handles of mechanics' tools, &c. and it has even been employed as a material for musical instruments. As an ornamental shrub, this species stands in the highest rank, and by the frequency of its growth and the brilliancy of its flowers, it contributes in a great degree to the elegance of the natural scenery in those mountains and woods, which it inhahits. When cultivated in gardens, it requires a soil which is somewhat moist, and a shady or northern aspect.
Kalmia latifolia, Lin. Sp. pl.
Curtis, Bot. Mag. t. 175.
Michaux f. Arbres forestiers, iii. 147, t. 5.
Pursh i. 296.
Chamaedaphne foliis tini, &c.
Catesby, Carolina, ii. t. 98.
Ledum floribus bullatis. &c. Trew, t. 38.
Cistus chamaerhododendros, &c. Plukenet, Phyt. t. 379, f. 6.
Kalm, travels, i. 335, &c.
Bart. Coll. i. 18, 48; ii. 26.
Thacher, Disp. 247.
Thomas, Inaugural dissertation.
American Medical Botany, 1817-1821, was written by Jacob Bigelow, M. D.