THE COHESION THEORY OF TRANSPIRATION

Abstract

The present explanation of the mechanism of water transport in plants (11, p. 9; 12, p. 231) includes, briefly, the pulling of continuous columns of water from the soil by means of evaporation from the leaves, the columns remaining, intact under the stress of great height and rapid evaporation because of the tensile strength of the water (6, 16, 20). WALTER (23, p. 67), after a discussion of experiments on water trans-port, says, "Damit scheint die Theorie der Wasserleitung, die auf der Kontinuitit der Wasserfiden von der Spitze bis zur Basis der Pflanzen beruht und deshalb als Kohasionstheorie bezeichnet wird, endgultig gefes-tigt zu sein, wenni auch im Einzelnen immer noch Veranderungen eintreten k6nnen. . . ... WNTOODHOUSE (24) reports experiments interpreted as indicating a need for modification of the tensile column theory. The experiments are: first, an inability, using Pittosporium undutlatturt and Ricimis co)nnuntis, to draw mercury to a height greater than 49 cm., and, second, a greater speed of