On green Organisms occurring in the lower Troposphere

1. A sampling-apparatus for aeroplankton was constructed and the exclusion of extraneous infection was ascertained by control-experiments. 2. The air-samples (in which about 1 cubic meter of air was filtered) from six airplane-flights during which 24 collections were made at different altitudes between 100—2000 meters, were examined and demonstrated the presence and active development of nine species of Algae, one species of Mosses and one species of Ferns. 3. The organisms appeared with different frequency-Chlorococcum being the most frequent. 4. The quantity of these organisms decreased at higher levels while repeatedly an appreciable number was found at 500 meters. 5. Meteorological factors exerted influence on the frequency of these organisms as a strikingly large amount of organisms was found after a noticeable dry period. 6. Air-samples taken from buildings by means of an airpump at altitudes of 14.5- and 30 meters and rain-water-samples showed similar organisms. A slime-mould and a diatom were observed in these lower levels. At this place I wish to express my most grateful thanks to Prof. Dr. L. G. M. Baas Becking for his invaluable advice and enthousiastic help during the time I worked at the Botanical Institute at Leyden.