When humans first gathered food plants into a garden, they simultaneously created an ideal habitat for insects to feed, initiating a battle for sustenance that continues to this day. For the largest part of human history, the insects have had the upper hand.
In the Colonial Garden at Colonial Williamsburg, we face the same challenge, but use centuries-old techniques to fight back.
The first English garden book, “The Gardeners Labyrinth” (1577) written by Thomas Hill, records:
“There is none so dul of eye-sight (as I believe) who not thorowly perceiveth and seeth, how that the Garden riches be diversly annoyed, and harmed by divers creeping worms and beasts, as wel above as under the earth, and that through the same occasion, often procured to feeble and wast, and unlesse speedy remedies shall be exercised, that these in the end do fall down and perish.”
The remedy, of course, has been the problem. In his book, Hill recommends many of the same techniques that had been practiced for more than a thousand years at the time and that continued well into the 19th century. Plants were sprinkled with fig tree ashes, ox urine, olive oil and the soot of chimneys. Sulfur, lixivium of limewater (a solution of slaked lime) and assafætida (an evil-smelling latex from the roots of several species of Ferula plants) were sprayed on the leaves. Bundles of garlic, brimstone (sulfur), goat hooves and hart’s horn were burned between the rows to ward off pests.
Pests born from the morning dew
For people of the time, the very origin of the insects that attacked the plants was a mystery. For more than a thousand years, gardeners believed insect and disease organisms arose through spontaneous generation. According to Aristotle, plant lice (aphids) arose from the morning dew and field mice were created by dirty hay.
One of the first scientific investigations into spontaneous generation was conducted by the Italian physician, Francesco Redi, in 1668. It was generally believed that maggots arose spontaneously in rotting meat, but Redi postulated that the organisms actually arose from the eggs laid by flies. To test his hypothesis, Redi set meat out in a number of flasks, some open to the air, some sealed completely and others covered with gauze. The maggots appeared only in the open flasks, proving that the flies had to be able to reach the meat to lay their eggs.
The debate over spontaneous generation continued through the 18th century. In 1745, the English clergyman John Needham conducted what he claimed to be the experiment that definitively settled the debate. After the invention of the microscope, it was readily apparent that boiling killed microorganisms. So, in his experiment, Needham boiled chicken broth in a flask and then allowed the liquid to cool. Within a few days, microorganisms had formed a scum on the surface of the broth, proving the theory of spontaneous generation, Needham claimed.
Lazzaro Spallanzani, an Italian priest, was not convinced. In 1768, he proposed that the microorganisms had been introduced from the air. In his experiment, he boiled meat broth in one flask that was allowed to stand open and in another that was sealed. The open flask grew microorganisms; the sealed flask did not. Doubters argued that this only proved that spontaneous generation could not occur without air.
In 1859, the French Academy of Sciences solicited experiments to prove or disprove spontaneous generation. A young French chemist named Louis Pasteur created the experiment that finally lay to rest the theory of spontaneous generation (decades before he developed the rabies vaccine). In his experiment, as others had in the earlier tests,
Pasteur boiled meat broth in a flask. But he modified the container by heating the neck of the flask and bending it into an S shape so that air could enter but airborne spores could not. The broth in the flask remained clear. In a definitive demonstration, he then tipped the broth into the lowest part of the neck, where spores had settled through gravity, and the broth rapidly clouded over. This not only disproved spontaneous generation, but also demonstrated the ubiquity of microorganisms in the air.
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