There are numerous varieties of the sweet orange. Maltese or blood oranges are characterized by the deep-red tint of the pulp, and comprise some of the best varieties. Gallesio refers to the blood orange as cultivated extensively in Malta and Provence; they are largely grown in the Mediterranean region in the present day, and have been introduced into America. The Washington or Bahia Navel and other so-called navel oranges have a navel-like mark on the apex of the fruit due to the production of an incipient second whorl of carpels forming a more or less abortive small or ange under the skin of the main one. Baptiste Ferrari, a Jesuit monk, in his work Hesperides, sive de malorum aureorum cultura et usus libri quatuor, published at Rome in 1646, figures and de scribes such an orange.
Citrus nobilis is the king orange, of which C. nobilis var deliciosa is the mandarin or tangerine orange. It is remarkable for its flat tened spheroidal fruit, the rind of which readily separates with the slightest pressure; the pulp has a peculiarly luscious flavour when ripe. The small tangerine orange, valued for its fine colour and fragrance, is a variety of loose-skinned orange now grown rather extensively in Florida and California. The Bergamot or ange (Citrus Bergamia) largely grown in Southern Italy and Sicily, yields the perfume. It is probably of hybrid origin.
Another loose-skinned orange, the Satsuma, introduced into the United States many years ago, is cultivated on a fairly large scale in the region bordering on the Gulf of Mexico in western Florida, southern Alabama, southern Mississippi and southern Louisiana. The Satsuma is the chief variety grown in Japan and is the earliest citrous fruit grown in the United States, ripening from the first of October to the first of December.
The fruit is a very wholesome article of diet, abounding in citric r cid, and, like the lemon and lime, possessing a high vitamin content.
Diseases.—Several are caused by fungi, others by insects. Of the fungus diseases that known as root-rot in Florida and mal-di gomma in Italy is very widely distributed. It occurs on the lower part of the trunk and the main roots of the tree, and is indicated by exudation of gum on the bark covering the diseased spot. The diseased patches spread into the wood, killing the tissues, which emit a foetid odour; the general appearance of the tree is un healthy, the leaves become yellow and the twigs and young branches die. A fungus (Phytophthora terrestris) is found asso ciated with the disease, which is also fostered by faulty drainage, a shaded condition of the soil, the use of rank manures and other conditions. For treatment, the diseased patches should be cut
away and the wound treated with an antiseptic. A very similar disease, brown-rot gummosis, occurs in California; it is caused by Pythiacystis citrophthora, and is treated in much the same way. The sour orange resists both root-rot and gummosis and is in con sequence largely used as root stock both in Florida and California.
Decay of oranges in transit often causes serious losses; this has been shown to be due to Penicillium, the germinating of which spores penetrate the skin of damaged fruits. Careful picking, handling and packing have much reduced the amount of loss from this cause. Another fungus disease, scab, has been very injurious to the lemon and sour orange and grapefruit in Florida. It is caused by Cladosporium citri which forms small warts on the leaves and fruits; spraying with a weak solution of Bordeaux mix ture or with ammoniacal solution of copper carbonate is recom mended. Citrus canker, a bacterial disease caused by Phytomonas citri, formerly caused much loss in Florida and nearby states. It has been eradicated at a cost of many millions of dollars. The sooty mould of the orange, which forms a black incrustation on the leaves and also the fruit, probably occurs wherever the orange is cultivated. It is caused by species of Meliola; in Europe and the United States by M. Penzigi. The fruit is often rendered unsale able and the plant is also injured as the leaves are unable properly to perform their functions. The fungus is not a parasite, but lives apparently upon the honey dew secreted by aphides, etc., and is therefore dependent on the presence of these insects. Spraying with resin-wash is an effective preventive, as it destroys the in sects. The diseases of citrus fruits have been very thoroughly studied during recent years. (See Fawcett's Citrus Diseases.) Several insect enemies attack the plant, of which the scale in sect Aspidiotus is the most injurious in Europe and the Azores. In Florida another species, Mytilaspis citricola (purple scale), some times disfigures the fruit to such an extent as to make it unfit for market. Several species of Aleyrodes are insect pests on leaves of the orange; A. citri, the white orange fly of Florida, is described as the most injurious of the insect pests of the crop in Florida at the present time; A. Howardi is a very serious pest in Cuba. The Mediterranean fly (Ceratitis capitata) proved very destructive to citrus fruit in Florida in the spring of. 1929. The government appropriated $4,000,000 in the hope of checking its ravages.