Many small garden flowers are very sensitive to changes in the weather. The scarlet pimpernel, for example, is sometimes called "the ploughman's weather-glass", and its rain-predicting capabilities have been celebrated more than once in rural rhyme. One such ditty, for example, tells us of The pimpernel, whose brilliant flower
Closes against the approaching shower, Warning the swain to sheltering bower From humid air secure.
But many others share this gift. The familiar bindweed, Convulus arvensis, for example, is similarly endowed, as is the common dandelion, Taraxacum. And the marigold, Calandula pluvialis actually boasts of this talent in its very name.
There are sound reasons, of course, why these flowers react to increases in humidity. They do so to avoid their pollen getting damp and germinating prematurely. And the closing movement can be very quick; the unfortunately named Bastard Toad-flax, for example, also more politely known as Thesium alpinum, closes up within 30 seconds of being moistened. Unfortunately, the reliability of any of these flowers as weather forecasters is marred by the fact that they close up anyway at night, and also respond to the dampness of a fog or mist in otherwise dry and very settled weather.
But the most celebrated case of horticultural perspicacity occurred a little over 100 years ago with the bizarre arrival of the "Weather Plant". The plant in question was Abrus precatorius, a member of the bean family that grows wild in India. It has a distinctly nervous disposition, so that if you touch even a single leaf the entire branch begins to fold up, and in 1887 it was harnessed to the services of meteorology by Josef Nowack of Vienna.
Nowack claimed to relate the movements of the plant to weather conditions quite some time ahead. When the leaves were horizontal, he maintained, it was a sign of change; when they sloped upwards, fine weather was on the way, and when they drooped bad weather was to come. Nowack, indeed, was soon quite carried away, and the repertoire of his weather plant was extended to include the speed and direction of the wind, predictions of both snow and fog, and estimates of the amount of atmospheric electricity in the air. This wonderful plant quickly caught the imagination of the public. Rigorous tests at Kew Gardens in Britain, however, showed that Mr Nowack was highly selective in his verification methods, achieving good results simply by including in his statistics only those forecasts which had turned out - by chance - to be correct. Nevertheless, he continued with moderate success to peddle the alleged prognostications of his weather plant until his death in 1918.