Unlike the orange, which presents a fine close head of deep green
foliage, it forms a straggling bush, or small tree, 10 to 12 ft. high,
with paler, more scattered leaves, and short angular branches with
sharp spines in the axils. The flowers, which possess a sweet odour
quite distinct from that of the orange, are in part hermaphrodite
and in part unisexual, the outside of the corolla having a purplish
hue. The fruit, which is usually crowned with a nipple, consists of
an outer rind or peel, the surface of which is more or less rough
from the convex oil receptacles imbedded in it, and of a white inner
rind, which is spongy and nearly tasteless, the whole of the interior
of the fruit being filled with soft parenchymatous tissue, divided
into about ten to twelve compartments, each generally containing
two or three seeds. The white inner rind varies much in thickness
in different kinds, but is never so thick as in the citron. As lemons
are much more profitable to grow than oranges, on account of their
keeping properties, and from their being less liable to injury during
voyages, the cultivation of the lemon is preferred in Italy wherever
it will succeed. In damp valleys it is liable like the orange (q.v.)
to be attacked by a fungus sooty mould, the stem, leaves, and fruit
becoming covered with a blackish dust. This is coincident with or
subsequent to the attacks of a small oval brown insect, Chermes
hesperidum. Trees not properly exposed to sunlight and air suffer
most severely from these pests. Syringing with resin-wash or milk
of lime when the young insects are hatched, and before they have
fixed themselves to the plant, is a preventive. Since 1875 this fungoid
disease has made great ravages in Sicily among the lemon and citron
trees, especially around Catania and Messina. Heritte attributes
the prevalence of the disease to the fact that the growers have
induced an unnatural degree of fertility in the trees, permitting
them to bear enormous crops year after year. This loss of vitality
is in some measure met by grafting healthy scions of the lemon on
the bitter orange, but trees so grafted do not bear fruit until they
are eight or ten years old.
The lemon tree is exceedingly fruitful, a large one in Spain or Sicily ripening as many as three thousand fruits in favourable seasons. In the south of Europe lemons are collected more or less during every month of the year, but in Sicily the chief harvest takes place from the end of October to the end of December, those gathered during the last two months of the year being considered the best for keeping purposes. The fruit is gathered while still green. After collection the finest specimens are picked out and packed in cases, each containing about four hundred and twenty fruits, and also in boxes, three of which are equal to two cases, each lemon being separately packed in paper. The remainder, consisting of ill-shaped or unsound fruits, are reserved for the manufacture of essential oil and juice. The whole of the sound lemons are usually packed in boxes, but those which are not exported immediately are carefully picked over and the unsound ones removed before shipment. The exportation is continued as required until April and May. The large lemons with a rougher rind, which appear in the London market in July and August, are grown at Sorrento near Naples, and are allowed to remain on the trees until ripe.
Candied lemon peel is usually made in England from a larger variety of the lemon cultivated in Sicily on higher ground than the common kind, from which it is distinguished by its thicker rind and larger size. This kind, known as the Spadaforese lemon, is also allowed to remain on the trees until ripe, and when gathered the fruit is cut in half longitudinally and pickled in brine, before being exported in casks. Before candying the lemons are soaked in fresh water to remove the salt. Citrons are also exported from Sicily in the same way, but these are about six times as expensive as lemons, and a comparatively small quantity is shipped. Besides those exported from Messina and Palermo, lemons are also imported into England to a less extent from the Riviera of Genoa, and from Malaga in Spain, the latter being the most esteemed. Of the numerous varieties the wax lemon, the imperial lemon and the Gaeta lemon are considered to be the best. Lemons are also extensively grown in California and Florida.
Lemons of ordinary size contain about 2 oz. of juice, of specific gravity 1.039-1.046, yielding on an average 32.5 to 42.53 grains of citric acid per oz. The amount of this acid, according to Stoddart, varies in different seasons, decreasing in lemons kept from February to July, at first slowly and afterwards rapidly, until at the end of that period it is all split up into glucose and carbonic acid—the specific gravity of the juice being in February 1.046, in May 1.041 and in July 1.027, while the fruit is hardly altered in appearance. It has been stated that lemons may be kept for some months with scarcely perceptible deterioration by varnishing them with an alcoholic solution of shellac—the coating thus formed being easily removed when the fruit is required for household use by gently kneading it in the hands. Besides citric acid, lemon juice contains 3 to 4% of gum and sugar, albuminoid matters, malic acid and 2.28% of inorganic salts. Cossa has determined that the ash of dried lemon juice contains 54% of potash, besides 15% of phosphoric acid. In the white portion of the peel (in common with other fruits of the genus) a bitter principle called hesperidin has been found. It is very slightly soluble in boiling water, but is soluble in dilute alcohol and in alkaline solutions, which it soon turns of a yellow or reddish colour. It is also darkened by tincture of perchloride of iron. Another substance named lemonin, crystallizing in lustrous plates, was discovered in 1879 by Palerno and Aglialoro in the seeds, in which it is present in very small quantity, 15,000 grains of seed yielding only 80 grains of it. It differs from hesperidin in dissolving in potash without alteration. It melts at 275° F.
The simplest method of preserving lemon juice in small quantities for medicinal or domestic use is to keep it covered with a layer of olive or almond oil in a closed vessel furnished with a glass tap, by which the clear liquid may be drawn off as required. Lemon juice is largely used on shipboard as a preventive of scurvy. By the Merchant Shipping Act 1867 every British ship going to other countries where lemon or lime juice cannot be obtained was required to take sufficient to give 1 oz. to every member of the crew daily. Of this juice it requires about 13,000 lemons to yield 1 pipe (108 gallons). Sicilian juice in November yields about 9 oz. of crude citric acid per gallon, but only 6 oz. if the fruit is collected in April. The crude juice was formerly exported to England, and was often adulterated with sea-water, but is now almost entirely replaced by lime juice. A concentrated lemon juice for the manufacture of citric acid is prepared in considerable quantities, chiefly at Messina and Palermo, by boiling down the crude juice in copper vessels over an open fire until its specific gravity is about 1.239, seven to ten pipes of raw making only one of concentrated lemon juice. “Lemon juice” for use on shipboard is prepared also from the fruits of limes and Bergamot oranges. It is said to be sometimes adulterated with sulphuric acid on arrival in England.
The lemon used in medicine is described in the British pharmacopoeia as being the fruit of Citrus medica, var. Limonum. The preparations of lemon peel are of small importance. From the fresh peel is obtained the oleum limonis (dose 12-3 minims), which has the characters of its class. It contains a terpene known as citrene or limonene, which also occurs in orange peel: and citral, the aldehyde of geraniol, which is the chief constituent of oil of roses. Of much importance is the succus limonis or lemon juice, 1 oz. of which contains about 40 grains of free citric acid, besides the citrate of potassium (.25 %) and malic acid, free and combined. Ten per cent. of alcohol must be added to lemon juice if it is to be kept. From it are prepared the syrupus limonis (dose 12-2 drachms), which consists of sugar, lemon juice and an alcoholic extract of lemon peel, and also citric acid itself. Lemon juice is practically impure citric acid (q.v.).
Essence or Essential Oil of Lemon.—The essential oil contained in the rind of the lemon occurs in commerce as a distinct article. It is manufactured chiefly in Sicily, at Reggio in Calabria, and at Mentone and Nice in France. The small and irregularly shaped fruits are employed while still green, in which state the yield of oil is greater than when they are quite ripe. In Sicily and Calabria the oil is extracted in November and December as follows. A workman cuts three longitudinal slices off each lemon, leaving a three-cornered central core having a small portion of rind at the apex and base. These pieces are then divided transversely and cast on one side, and the strips of peel are thrown in another place. Next day the pieces of peel are deprived of their oil by pressing four or five times successively the outer surface of the peel (zest or flavedo) bent into a convex shape, against a flat sponge held in the palm of the left hand and wrapped round the forefinger. The oil vesicles in the rind, which are ruptured more easily in the fresh fruit than in the state in which lemons are imported, yield up their oil to the sponge, which when saturated is squeezed into an earthen vessel furnished with a spout and capable of holding about three pints. After a time the oil separates from the watery liquid which accompanies it, and is then decanted. By this process four hundred fruits yield 9 to 14 oz. of essence. The prisms of pulp are afterwards expressed to obtain lemon juice, and then distilled to obtain the small quantity of volatile oil they contain. At Mentone and Nice a different process is adopted. The lemons are placed in an écuelle à piquer, a shallow basin of pewter about 812 in. in diameter, having a lip for pouring on one side and a closed tube at the bottom about 5 in. long and 1 in. in diameter. A number of stout brass pins stand up about half an inch from the bottom of the vessel. The workman rubs a lemon over these pins, which rupture the oil vesicles, and the oil collects in the tube, which when it becomes full is emptied into another vessel that it may separate from the aqueous liquid mixed with it. When filtered it is known as Essence de citron au zeste, or, in the English market, as perfumers’ essence of lemon, inferior qualities being distinguished as druggists’ essence of lemon. An additional product is obtained by immersing the scarified lemons in warm water and separating the oil which floats off. Essence de citron distillée is obtained by rubbing the surface of fresh lemons
