He illustrates his remarks from the chief sciences, as in Astronomy, by its importance in understanding the laws of storms and tides, which Whewell was then studying. Agriculture was touched upon, in showing the importance of a knowledge of Vegetable Physiology, and illustrated by the parasites, yellow Rattle and Wheat-rust. He insisted upon the educational value of accuracy, demanded of the scientist, and the avoiding _a priori_ assumptions and hastily drawn deductions from insufficient data. But even the philosopher himself does not always escape from the imputation; for the farmers at Hitcham were firmly convinced that the "Piperage" or Barberry _itself_ blighted the wheat. The Professor could not convince them that the red colour of the spots on the leaves of the bush was not due to the same fungus as that on the wheat. Indeed, he observes (in a MS.): "It is not likely (as some suppose) that it is due to the influence of _Æcidium berberidis_." We now know that the farmers were nearer the truth and the botanists were wrong. But one point the Professor established--and I possess his dried specimens to this day--and that was, that the "mildew," a black fungus, subsequently arises from the same substratum or mycelium as the rust. The mildew, then, throws off orange-coloured dust-like "spores," which attack the Barberry, and so the cycle is completed[103]. I still possess his dried specimens of other species of _Æcidium_ attacking various kinds of plants, which he collected for comparison with that of the Barberry. As abortive attempts to find coal had been made in some counties, he pointed out the value of Geology in at least intimating where coal was possible and also where it was impossible. It was not, he said, that a "little knowledge is a dangerous thing," as no one would become learned if he did not begin with a little, but it was the hasty deductions that were valueless and often dangerous. As a practical illustration of this under the false assumption that the roots made the "bulb" of mangold-wurzel, he noticed the common practice of stripping off the leaves of plants, and explained to them that unless they were required for fodder, it was a wasteful practice, as the leaves (and not the roots, as they supposed) were the makers of the "bulbs." Indeed, in 1860, Prof. Jas. Buckman proved that it lessens the weight of mangold-wurzel by nearly one half. Science was not even shut out at the Hitcham Horticultural Society's Exhibitions, for he always had his own marquee erected and a large board over the entrance with "The Marquee Museum" upon it, the letters being composed of Hitcham fresh-water mussel shells. During the day of the show, he would deliver "lecturets" from time to time on the various specimens exhibited.