1832 



A TEXTBOOK OF THEORETICAL BOTANY 



four or five sepals and the same number of petals. The stamens are often 

 double the number of petals and the ovary is composed of four or five 

 carpels with one or two ovules in each loculus. 



The most important genus is Citrus, which contains ten species distri- 

 buted throughout the Old World. They are trees or shrubs with simple 

 leaves. Axillary spines derived from a leaf of a branch shoot occur in most 

 species. The calyx and corolla are composed of from four to eight 

 segments (Fig. 1733). The stamens are joined in irregular bundles 

 corresponding in position to the sepals and the gynoecium consists of six 



Fig. 1733. — Citrus medicn \ar. liniouiim. Lemon. Flower in 



longitudinal section. 



or more carpels. The fruit is a large berry, or hesperidium, with a leathery 

 pericarp and the flesh is formed of succulent hairs which grow out from the 

 inner layers of the pericarp. 



The Citrus fruits form a very important article of commerce. C. 

 aiiranthim is the Orange, which probably originated in northern India and 

 Assam. It has been in cultivation possibly since 1500 B.C. C. limonum is 

 the Lemon. That at present in cultivation was derived from a variety 

 collected in Peking in 1908 and is considered far superior to the older 

 forms. C. medica is the Citron, and, according to some, the Lemon, the 

 Lime and the Sweet Lime are varieties of it, the last two being botanically 

 var. acida and var. Umetta respectively. C deciimana is the Shaddock or 

 Pomelo, while a variety, or possibly a separate species, C. paradisi, is the 

 Grapefruit. This important fruit is thought to have originated from a 

 West Indian sport from the Shaddock. The Mandarin Orange is C. nobilis, 

 while a number of hybrids are also cultivated. The whole question of the 

 Citrus fruits will be more fully considered in Volume IV. 



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