Studies of the Physiology of Coffea Arabica III. Transpiration Rates Whole Trees in Relation to Natural Environmental Conditions

Abstract

WHEN automatic Balls chain (1937) balance1 described a valuable a method instrument of weighing was by made the use available of an automatic chain balance1 a valuable instrument was made available to the plant physiologist. It has always been recognized that the weighing of rooted plants grown in sealed containers is the only sound method for determining transpiration rates. But, especially where large plants are used, the weight of the plant and its container is very great compared with the weight-changes to be measured, and large balances are seldom sensitive. Consequently measurement of weight-loss over short time-intervals has been impossible. Balls claimed that his method enables weighing to be made on a steelyard with an accuracy approaching that of a good chemical balance, and quotes data illustrating an accuracy of 1: 3 50,000. I have used a modification of his method and have found that his claims can readily be confirmed and are in fact conservative. Thus it becomes possible to record the march of the transpiration rate of large plants over very short time-intervals, and the relation between the march of transpiration rates and the varying meteorological factors can be studied in a way hitherto impossible.