An Attempt to Record Internal Tree-Trunk Pressures

Abstract

The terms root pressure, exudating pressure, have become familiar to plant physiologists. Chase' gives an excellent historical review of the literature and no further citations will be made in this paper. Most, if not all, workers dealing with gas pressures in plants have attempted to measure such forces by employing wateror mercury-filled manometers. Manual readings have been taken at irregular intervals, and very few automatic timing devices have been used or continuous records obtained. The writer recognized the need of a more elaborate investigation of internal pressures when engaged in a study of pruning paints and fungicides. Trunk cavities had been made in a manner acceptable to professional tree surgeons, but instead of being filled with concrete or some other material they had been covered with heavy plate glass cut to the correct size. Less elaborate ones had been made by drilling holes in the tree trunk and inserting the proper-size watch-glass. Without exception the glasses were either broken or were forcibly ejected from their anchorage in the matrix near the bark edge. An examination showed that they were literally blown outusually within twenty-four hours after installation. It was felt that pressure measurements would furnish the information needed to devise more substantial anchorages and covers more suitable than glass. Water-filled manometers were attached either to the trunk through a bored hole, or directly to the cavity through a vent tube. A record of the internal pressure-back of a glass-front cavity-as shown by a water-filled manometer follows: