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"And this also I have observed, that any tulip thus changing its original colour is usually ruined afterwards and wanted only to delight its master's eyes with this variety of colours before dying, as if to bid him a last farewell."
Ranging from red to purple, anthocyanin pigment is contained in the epidermis of the tulip petal and is its primary color. Beneath this skin is another layer of cells, the mesophyll. When a tulip "breaks," pigments that otherwise would be evenly diffused become separated, allowing the underlying white or yellow color of the mesophyll to show through. As if by magic, a plain tulip of uniform color is transformed into one that is spectacularly variegated, with vivid flames running up the middle of the petal or feathered along the edges. This phenomenon occurred within several decades of the tulip being cultivated in Europe and first was described by Carolus Clusius, a professor of botany in Leiden, who attempted to illustrate these variations in the 1583 woodcut below.
Although a virus was presumed to be responsible, it was not known what prompted a flower to break, only that it was weakened as a result. In 1927, working at the John Innes Horticultural Institution (now the John Innes Institute), Dorothy Cayley discovered that, in transferring infected tissue from broken bulbs to healthy ones during their dormant state, the Tulip Breaking Virus that caused the break in color was transferred as well. The next year, she demonstrated that aphids were the vector.
Variegated flowers, such as the one illustrated above, now are cultivated deliberately and are not the result of viral infection.
References: "'Breaking' in Tulips" (1928) by D. M. Cayley, Annals of Applied Biology, 15(4), 529-539; "'Breaking' in Tulips. II" (1932) by Dorothy M. Cayley, Annals of Applied Biology, 19(2), 153-172; "Aphis as a Possible Vector of 'Breaking' in Tulip Species" (1930) by A. W. McKenny Hughes, Annals of Applied Biology, 17(1), 36-42; "The Antithetic Virus Theory of Tulip-Breaking" (1938) by Frank P. McWhorter, Annals of Applied Biology, 25(2), 254-270; "'Broken' Tulips and Tulip Breaking Virus" (May 2005) by John Walsh, Microbiology Today, 68-71; "The Development of the Virus Concept as Reflected in Corpora of Studies on Individual Pathogens: 3. Lessons of the Plant Viruses–Tobacco Mosaic Virus" (1976) by Lise Wilkinson, Medical History, 20(2), 111-134; A Treatise on Tulips by Carolus Clusius of Arras (1951) translated by W. van Dijk; "Historical Sketch of Tulip Mosaic or 'Breaking.' The Oldest Known Plant Virus Disease" (1933) by M. B. McKay and M. F. Warner, National Horticultural Magazine, 12, 179-216. The woodcut is from Clusius' Rariorum aliquot stirpium, per Pannoniam, Austriam, & vicinas quasdam provincias observatarum historia (1583).
See also Carolus Clusius.
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