Citrus paradisi

Grapefruit. Now popular as a breakfast dish, this mildly bitter, acidic fruit is one of the largest citrus fruits. It is of relatively recent origin and is thought to be a chance hybrid between two other Citrus spp. The name 'grapefruit' was apparently used for the first time in Jamaica in 1814, but its etymology is obscure. Citrus reticulata

Mandarin, or tangerine. Often known as the 'loose-skinned' oranges because of their easy peeling, these fruits are used mainly as a dessert. They probably originated in Vietnam and are of ancient cultivation in China and Japan. Citrus sinensis

Sweet orange. This is the most important of the citrus fruits, in terms of acreage, and it is now used mainly as a fresh juice at breakfast in order to provide a daily dose of Vitamin C. There are three main types of cultivar. Navel oranges have a second row of carpels opening at the apex with the appearance of a 'belly button' or navel. Blood oranges have a red, or streaky red pulp. Thirdly, there are cultivars with normal fruits. 'Valencia' is the most important commercial cultivar, followed by 'Washington Navel' and 'Jaffa'. Claviceps purpurea

The fungus that causes ergots and ergotism. The fungus infects the stigma of an open-pollinated cereal, such as rye, or various species of open-pollinated fodder grasses. The seed is then transformed into a black fungal body that is the ergot and is poisonous. Ergotism used to be a serious problem in the rye districts of eastern Germany, Poland, and western Russia, where wheat is difficult to grow. This problem was largely solved by the introduction of potatoes. Clay

1. Clay minerals are kaolin, mica, talc, and similar groups. 2. Clay is a component of soils, with a particle size of less than two microns. 3. Clay soils contain at least 20% clay particles and are described as heavy soils.

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