This is closely related to the orange, as is indicated in horticultural practice in the choice of stocks. The lemon is often budded on the orange and the orange on the lemon on an extensive commercial scale. In the great lemon-growing centres on the Mediterranean the rough lemon is the favorite stock for the orange.
Lemon and orange hybrids are also frequently produced, but they have no commercial status, as they do not answer the purposes for which either oranges or lemons are grown. The lemons of the old California missions were of large size, the juice was low in acidity, and the rinds were more or less bitter. It was not until varieties were brought from the Mediterranean lemon-growing centres with fruit of proper size, percentage of acids, thinness of skin, and freedom from bitter rinds, that growers were able to compete successfully with those shipped from Sicily, Sardinia, and Spain. During the past fifteen years the output from the west coast of lemons has been a surprise to the Mediterranean growers, as over 1200 car-loads annually have recently reached the markets east of the mountain ranges.
The lemon is not as hardy as the orange. Its fruit, foliage, and wood will be seriously injured by a freeze that the orange will endure without serious injury. But this is not surprising, as the varieties from Sicily and extreme south France are the outgrowth of ages of selection in the soft mild climate of the great inland sea, where frost is unknown and where soil and air are never dry on the 10th parallel of latitude.
It is not probable that it would require a long period for a skilled expert, such as Burbank, of Santa Rosa, California, to develop, by crossing and selection, varieties of the lemon such as the market now requires from the varieties of the mountains of north India at a height of four thousand feet. If this can be accomplished, we might secure varieties hardier than the orange, with a more compact form, that would be less troublesome to keep in shape by perpetual pruning.
In south Florida the lemon is budded almost exclusively on seedlings of the sour orange, and the same is true in California, as common experience has shown that on this stock the lemon-trees have a better habit of growth, the fruit averages less in size, and the tree seems to be some healthier and hardier. Where the Citrus trifoliata has been used, it has seemed to increase hardiness and the growth is less riotous than when on sour-orange or rough-lemon roots.
The pruning of this rampant-growing tree seems as yet to be an unsettled problem, and growers differ materially as to methods. Many growers annually shorten the long leaders and rampant points of growth in the partially dormant season. Later in the season a large part of the shoots that start as an effect of the winter cutting back are cut out. Others are content with more moderate shortening and pinching points of growth, which results in an equal quantity of sizable fruit, but a less symmetric and compact form of tree. Upon the whole, it is a troublesome tree to manage, but to the methodic grower in a nearly frostless region it is one of the most profitable of the orchard fruits.
The fruit is gathered, when it attains proper size for shipping, when wholly green and not more than half grown. The crop for summer use is mainly gathered in the winter and stored in what is known as a curing-house, built in such way as to be dark and free from sudden changes in temperature, yet with such an admission of air as will carry off the evaporation from the fresh green fruit. In these houses the lemons slowly mature and while taking on the golden color the rind is toughened, which favors long keeping. The proper curing requires the same methodic care and skill as does the pruning and management of the tree.