Tulipomania - Mike Dash [27]
Even in Clusius’s day it was obvious that something strange was happening to the tulips grown in Leiden and elsewhere. A bulb that one year had produced a unicolored tulip might become a Rosen or a Bizarden the next. This process was known as “breaking,” and the bulb of a flower that had undergone the process was said to be “broken” while those that remained unicolored were called “breeders.” The whole process was extremely unpredictable. There was no way of telling if or when a flower would break; one tulip might bloom in the spring with a dazzling new array of colors, while another, of the same variety and planted next to the first in the same flower bed, remained quite unaffected. Breaking was common in some years, less so in others. Similarly, a broken bulb might—albeit rarely—produce an offset that turned out to be a breeder, and no grower could be sure that a breeder bulb would not break. The only certainties seemed to be that tulips grown from seed were invariably breeders and that, once broken, a mother bulb would never again produce a unicolored flower.
There were clues here to the nature of the disease, and Clusius was a careful enough observer to notice that broken tulips were slightly smaller and definitely weaker than the flowers produced by breeder bulbs. But at a time when the mechanisms by which diseases are communicated remained unguessed at, the phenomenon of breaking seemed akin to magic to most of his contemporaries. Try as they might, growers could not force a breeder bulb to break when they wanted it to. Some turned to alchemical potions made of pigeon dung, which they applied to the bulbs; others tried cutting the bulbs of two different-colored tulips in two and binding the opposing halves together in the hope of producing a flower sporting both colors. These devices rarely had the desired effect.
Exactly when the tulip became infected with a virus is not certain. The earliest observations of the phenomenon date to about 1580, but the disease was probably older than that. In truth the plant became vulnerable to disease as soon as it entered a garden; any flowers raised in artificial proximity by humans face threats they do not encounter in the wild. Cultivars may be poorly cared for or discarded in favor of some new favorite, but in particular they can pick up diseases to which the more robust botanical species have developed an immunity or that at least spread more slowly in the wild.
The mystery of breaking remained unsolved until well into the twentieth century, when the agent that causes the disease, sometimes called the mosaic virus, was finally identified by staff at the John Innes Horticultural Institution in London. By permitting aphids to feed on broken bulbs and then on breeders, they were able to show that the breeder bulbs visited by the aphids broke twice as often as a control sample—thus simultaneously proving that the disease was caused by a virus and demonstrating the mechanism whereby it was transmitted from one tulip to another. Further experimentation showed that the mosaic virus could infect both a flower when it was growing in a garden and a bulb that was being stored prior to planting. Perhaps ironically, given the efforts of old Dutch growers to induce breaking by binding half-bulbs together, the method used at the John Innes Institute to persuade aphids to feed alternately on infected and uninfected tulips was to graft halves of broken bulbs onto breeders.
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