EUPHRASIA is one of those genera exhibiting a very limited range of variation, as compared with Ranunculus, Senecio, Solatium or Euphorbia; yet abounding in closely allied forms, concerning the rank of which there is great diversity of opinion amongst botanists. Bentham and Hooker in their various works, including a monograph of the genus by the former, estimate the number of species at about a score, whilst the author of the monograph under consideration defines nearly a hundred. Whatever our opinion may be respecting the utility of this extreme subdivision, most of us will agree that a profound study of the manner and extent of this limited kind of variation should furnish some interesting results. Moreover the genus Euphrasia is admirably suited for this purpose, because it is possible to have the entire plant in all cases. Monographie der Gattung Euphrasia. Von Dr. R. von Wettstein. 4to. Pp. 316. With 14 plates and 4 maps. (Leipzig: Wilhelm Engelmann, 1896.)