Although L. stæchas was well known to the ancients, no allusion unquestionably referring to L. vera has been found in the writings of classical authors, the earliest mention of this latter plant being in the twelfth century, by the Abbess Hildegard, who lived near Bergen-on-the-Rhine. Under the name of Llafant or Llafantly, it was known to the Welsh physicians as a medicinal plant in the thirteenth century. The best variety of L. vera—and there are several, although unnamed—improved by cultivation in England, presents the appearance of an evergreen undershrub of about two feet in height, with grayish green linear leaves, rolled under at the edges, when young; the branches are erect and give a bushy appearance to the plant; the flowers are borne on a terminal spike, at the summit of along naked stalk, the spike being composed of six to ten verticillasters, more widely separated toward the base of the spike; in young plants two or four sub-spikes will branch alternately in pairs from the main stalk; this indicates great vigor in the plant, and occurs rarely after the second year of the plant's growth. The floral leaves are rhomboidal, acuminate, and membraneous, the upper ones being shorter than the calyces, bracteas obovate; the calyces are bluish, nearly cylindrical, contracted toward the mouth, and ribbed with many veins. The corolla is of a pale bluish violet, of a deeper tint on the inner surface than the outer, tubular, two-lipped, the upper lip with two and the lower with three lobes. Both the corolla and calyx are covered with stellate hairs, among which are embedded shining oil glands, to which the fragrance of the plant is due. The L. vera was identified in 1541, and introduced into England in 1568, flourishing remarkably well under cultivation, and yielding an oil far superior in delicacy of fragrance to that obtained from the wild plant, or to that obtained from the same plant cultivated in any other country.
When it is remembered that north of the 50th degree of latitude the vine yields little but garlands of leaves, and that we should attempt in vain to cultivate the olive north of the 44th degree, it may seem strange that the Lavandula vera, which is a native of about the same climate as these, should resist, unprotected, the vigorous frosts of this country. Even at Upsala, latitude 59° 51' N., in the Botanic Garden, it merely requires the shelter of a few branches to protect it in the winter; but this hardiness may be accounted for by several physiological reasons. Like all fruticulose labiates which have a hard compact tissue and contain much oily matter, the lavender absorbs less moisture than herbs which are soft and spongy, and, as it always prefers a dry calcareous, even stony, soil, the northern cultivators find that by selecting such localities the tissues of the plant take up so little water that the frost does not injure them.
In a northern climate the length of the days in summer, and the natural dryness of the air, compensate in some measure the reduction of temperature, and mature the plant only to the extent sufficient for the purpose for which it is grown. Perhaps the suspension of vital action during winter, which must be more complete in northern latitudes, as our frosts are more severe, tends to preserve certain plants, native of the south, for it is observed that all plants are more sensitive to cold when vegetation is active than when it is at rest. The vine is an instance of this. On the other hand, when the plant is cultivated further south than its natural boundary, the same causes seem to exert their influence, but in the reverse sense. Lavender is cultivated on the mountains of Yemen, in Arabia; the humidity, increasing inversely to the latitude, compensates the exhaling force of the sun's rays, and the elevation of the locality the effects of the heat.
Thus is confirmed, both in north and south, the law of vegetable physiology observed by De Candolle, in the temperate climates of France, and published in his "Essai de Geographie Botanique," that "plants can best resist the effects of cold in a dry atmosphere, and the effects of heat in a humid atmosphere." A mild, damp winter, like the one of 1889-1890, does more harm than a hard, seasonable frost, as the plants are apt to make green shoots prematurely, and the late frosts nip off these tender portions, each of which would otherwise have produced a flower spike.
The very severe winter of 1890-1891 did not kill so many plants as the one of 1889-1890. The stems and branches of lavender being ligneous and strong are able to resist the force of the wind, and the plant thrives best in a perfectly open locality, where the air circulates freely; the oil and resin which it contains in abundance enable it to resist the parching action of the wind and sun. Thus, on the most arid and sterile ground on the mountain sides in the south, and especially in Spain, plants of this genus flourish with more vigor in the season when most other vegetation is scorched up by the ardent rays of the sun, and the Lavandula vera seems to have a predilection for such spots.
Certainly the plants then assume a more stunted appearance than in richer soil, but at the same time the perfume is stronger and sweeter. The calyces become charged with oil glands, and yield a greater abundance of volatile oil.
In a very moist soil the water penetrates too much into the tissues, detaches the bark, the plant blackens at the root, and a white fungus attaches to the main stem and lower branches; it becomes feeble, diseased, and dies. A rich soil furnishes too much nutriment, the plant grows very large and herbaceous, becomes overcharged with water relative to its assimilating and elaboratory power, especially if growing in a cold climate, and the equilibrium of the chemical proportions necessary for the formation of natural juices becomes deranged at the expense of quantity and quality of the volatile oil produced.
These facts, long ago pointed out by Linnæus, have been verified in England. Some years ago a disease manifested itself in most of the plantations, which, not being understood by the growers, was not remedied (in fact, is not generally understood and remedied at the present time), the acreage under cultivation decreased, and, partly owing to this and a scarcity occasioned by a failure in the crop, the price of the oil rapidly rose from 50s. to 200s. per lb. Consequently, with the continually increasing demand and the continued rise in price, manufacturers of lavender water and of compound perfumes in which oil of lavender is a necessary ingredient commenced to buy the French oil, and venders of the English oil commenced to adulterate largely the English with the French oil.
By degrees the French oil become almost entirely substituted in England for the English, and at present it is difficult to purchase true English lavender water of a quality equal to that vended twenty years ago, except at a few first class houses.
The exorbitant profits demanded by chemists and druggists, and the incomprehensible will of the public to buy anything cheap, however bad, have encouraged a marvelous increase in the figures of the imports of French (and German, which is worse) oil.