In several communications made to this Society and to the British Association, I have announced the results of a series of observations on the distribution of Fluorine throughout the mineral, vegetable, and animal kingdoms. To myself, the least satisfactory part of these investigations has been the inquiry into the presence of fluorine in plants, for I have been more frequently foiled than successful in my attempts to detect it in them. Others have not, apparently, been more successful. Daubeny was as unable as Sprengel at an earlier period had been, to obtain evidence that the element under notice is present in vegetable structures; and Will of Giessen, the discoverer of fluorine in plants, speaks only of “traces” of it having been detected in barley. Later observers have not spoken more confidently concerning its abundance in vegetables; and in the many analyses of the ashes of plants which have recently been published, it seldom, if ever, finds a place.