Logarithmic Series and the Index of Diversity as Applied to Ecological Problems IN a recent paper in the Journal of Animal Ecology (32, May 1944), Dr. C. B. Williams of the Rothamsted Experimental Station discusses this subject. He describes the application of a logarithmic series to a number of problems. It is found to fit extremely well to a large number of frequency series whether they be taken from insects, birds or plants. It also fits well to the number of genera with different numbers of species in standard classifications of groups of both animals and plants. The idea of the index of diversity is applied to problems of the number of species of plants on different areas and to the comparison of floras of different areas with interesting results. The author gives a classification of the 171 families of dicotyledons according to their index of diversity. It is hoped in this way to stimulate discussion of the factors which control differences and resemblances in this index. As a general rule it is found that those families with numerous species and genera have a large index of diversity, but yet there may be a very wide range of index in families of about eqiial size. This paper is one of considerable interest and deals in the main with problems of species, area and numbers of individuals and with the grouping of species into genera, many examples of both being quoted.