Total absence of plastid pigments causes a sector of a leaf or stem to have white patches. This condition is termed variegation (Metrosideros). Variegation is produced when there is a cell mutation (cytological chimera), and all cells produced from that mutant mother cell lack the pigments, either because plastids are not present or the plastid cannot complete the manufacture of the pigment apparatus. White, therefore, is where color is missing. The zones where chloroplasts are not present are zones where no photosynthesis will occur, hence a variegated leaf has a lowered potential to fix carbon dioxide into sugars, and as a consequence, a variegated plant also tends to grow more slowly. Variegated leaves occur rarely in nature but are extremely common among indoor and outdoor ornamentals, where they have been saved as horticultural oddities. Species with variegated individuals are sometimes found in the understory of tropical rain forest, and this habitat is the source of a number of variegated house plants. The appearance of variegation in the tropical forest understory, if not simply by accident, has not been given a plausible explanation. Some variegated ornamentals have only a fringe of white around the leaf (Example: Pittosporum), sometimes irregular dots (Examples: a bromeliad and Begonia) and spots (Examples: Dieffenbachia, an aloe, and an orchid), sometimes broad panels of white (Examples: a bromeliad, shell ginger, Pisonia, and a fig), and even an occasional leaf that is totally achlorophyllous (white; Example: Hedera helix). Among monocotyledons, strips of stem internode may also be achlorophyllous (Example: variegated sugar cane). On a single plant, you can observe leaves with all different degrees of variegation, but a plant may also produce individual leaves or entire shoots that are all green (Examples: Coprosma, Abutilon, Euonymus, and Bougainvillea), and which did not involve mother cells with mutant plastids. On the same...
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