From the text...SUMMARY: '(1) A comparison is made between the visual method of ascertaining the frequency of a species, and a statistical method. The general agreement is noted and the advantages of each mentioned. (2) Using the statistical method a comparison of certain areas on Harpended Common is made and the full succession after burning shown to be Rumex acetosella-Holcus lanatus-Agrostis sp. (3) Edaphic factors whose intensity is likely to be altered by the burning are estimated by suitable means, and of these the lime requirement and humus content show a gradation accompanying the progress of the succession. (4) On the basis of the evidence available, the nature of the acidity, and its probable relation to the succession, to the formation of humus and to burning is discussed.'