chunk: "The cowslip (Primula veris) has two kinds of flowers in nearly equal proportions: in the one the stamens are long and the style short, and in the other the reverse, so that in one the stamens are visible at the mouth of the tube of the flower, in the other the stigma occupies the same place, while the stamens are halfway down the tube. The fact had been known to botanists for 70 years, but had been classed as a case of mere variability, and therefore considered to be of no importance. In 1860 Darwin set to find out what it meant, since, according to his views, a definite variation like this must have a purpose. After a considerable amount of observation and experiment, he found that bees and moths visited the flowers, and that their proboscis become covered with pollen while sucking up the nectar, and further, the pollen of a long stamened plant would most surely be deposited on the stigma of the long styled plants, and vice versa. Now followed a long series of experiments, in which