This book, submitted as thesis in 1959, is the result of intensive field work during three years in the forests of Suriname. A general description of the investigated areas is given in the introduction. Part one deals with the results of numerous microclimatological observations made at various levels in parallel series in the mesophy tic or rain forest and in large openings; besides a number of readings were taken in an adjacent drier vegetation type, the savanna forest. After a survey of the general climate the following factors are treated in their daily and seasonavariation: light intensity measured with a spherical electric photometer, athmosl pheric humidity recorded with hygrographs with psychrometer readings as controls, evaporation by Piche evaporimeters, air temperature recorded with thermographs and checked by standard and max-min. thermometer readings, and soil temperature by soil thermometers. As a result of the lucky circumstance that the main dry season of 1957 was exceptionally long and severe the measurements cover almost the whole range of climatic conditions in the investigated region. The author has paid much attention to the ways of both physical and mathematical treatment of his observations and to the value which can be attributed to the calculated figures. Also comparisons have been drawn with data published from other tropical countries.