PROF. CZAPEK'S pamphlet contains most important experimental work upon one of the fundamental physical attributes of the living protoplasmic cell, namely, the surface-tension of its external limiting layer. He makes it clear that the tension conditions obtaining in this layer, which intermediates between each metabolic unit and its environment, are of great significance for secretion and for absorption, and he has established that the surface-tension of the cells of the higher plants is maintained fairly constant at the value of about 0.685, the surface-tension of water in contact with air being taken as unity.
Ueber eine Methode zur direkten Bestimmung der OberflÃ chenspannung der Plasmahaut von Pflanzenzellen. By F. Czapek . Pp. iv+86. (Jena: Gustav Fischer, 1911). Price 2.60 marks.