The author, who, for some years past, has been studying from several angles and in quantitative way the relation between plants and their surrounding conditions, has been able to deduce from time to time some results, which are of some significance from the view-point of forest ecology and which may help support the conception of so-called phytometer. The subject-matter of ecology, the interrelation of plants with their surrounding conditions, naturally require very careful treatment and is one perhaps that can only be approached with power of inventive conception. To meet such a requirement, very close observation and ample experiments based on exact measurements, such as we now see carried on in the fields of morphology and physiology may be essential. Just such quantit a tive studies in ecology are now being fast introduced into the field of forestry, thus giving ride to the conception of plant-indicators or phytometers. The conception of plant-indicators or phytometers is really one of wide application, and almost any feature of plant life may be regarded as admitting such conception. However, such feature as the variation in histological structure and also of physiological process of plant, as it may easily admit of quantitative treatment, may have the great likelihood of well developing such conception. Among some new facts of plant life which the author in his study has been able to observe and which may be found useful as phytometer, the value set to wavyness in the lateral walls of epidermal cells in the leaves of some special plants as Taraxacum albidum and the ratio of the value of absorption to that of transpiration may stand somewhat prominent. The author fully believes that such quantitative studies as he has carried on will go to add to the practical value of phytometer used in the field of forest ecology.