Pfeffer's Studies of the Root Growth Pressures Exerted by Plants

HE pressure exerted3 and work performed by roots durT i n g orowth are important considerations in evaluating the effect of soil physical properties on plant growth. Data on experiments to measure such pressures appear in a paper by W. Pfeffer, “Druck und Arbeitsleistung durch Wachsende Pflanzen” published in Abbandlungen der Koniglzcb Sacbsiscben Gesellscbaft der Wissenscbaften, 33 :23 5-474, 1893. Since this paper is absent from American soils literature the following review is presented to add to the data and to stimulate further interest in such measurements. The basic principle of Pfeffer’s measurements of root pressure was to encase a portion of the root of a seedling plant in a plaster of Paris block in order to provide a base against which the growing root could exert pressure to move a second block that was cast around the’exposed tip or side of the root. Movement of the second block would compress a calibrated spring providing a measure of root elongation or expansion and the pressure exerted by the root. Figure 1 shows the arrangement of Pfeffer’s apparatus.