Appendix. Report on diatom flora from Hawkes Tor, Cornwall

Abstract

A sample of the diatomite collected from the base of the lower muds and peats at the kaolin china-clay pit at Hawks Tor, Bodmin, was submitted to me by Dr Godwin. In it sixty-three species of diatoms were found, of which a number were represented by more than one variety, there being seventy-four different forms in all. A list of these is given below in which the relative abundance, the present geographical distribution and the ecological preferences of each diatom are indicated. The names in this list are applied in the sense adopted by Hustedt (1930) in the latest comprehensive account of the diatoms of the fresh waters of western and central Europe. Some of the nomenclature adopted in that work is, however, not in accordance with theInternational Rules, and where this is the case the legitimate name has been used, or a new and legitimate combination made. Mills (1933-5) or Ross (1947) provide the synonymy necessary to relate these legitimate names to those used by Hustedt. No objective value for the relative frequency of the various diatoms could be obtained as any procedure based on counting was made impossible by the number of broken valves present. A subjective estimate was therefore made for each species using the terms conventionally employed in plant-ecological field-work. Most diatoms have a very wide geographical distribution, but it proved possible to group the forms found into four classes according to whether or not they are at present generally distributed in western and central Europe and whether they are as common there as farther north or south. The geographical divisions adopted are as follows: Arctic-alpine: known at present only from northern Europe or from high altitudes in the mountains of central Europe.