The most important application of thermocouple psychrometry will come from its 

 further development and subsequent application to measurements of the water status in 

 the soil -plant continuum under natural conditions. Previous attempts to understand the 

 dynamic relationships between the energy status of water in soils and plants have been 

 severely limited because the natural equilibrium was disturbed by removing samples from 

 the system. It would appear that for in situ determinations of soil water potential and 

 plant water potential of stems, the instrumentation presently available will provide 

 accurate estimates of the energy status of water. This is not to say, however, that 

 further improvements in the design and operation of thermocouple psychrometers are not 

 needed. Certainly, the work of Hoffman and Splinter (1968a, 1968b), Rawlins and others 

 (1968), and other workers, and -particularly the development of the double-junction psy- 

 chrometer, indicate that the in situ measurement of leaf water potential is now a 

 definite possibility. My own experience with the doub le- junction psychrometer for meas- 

 uring in situ leaf water potentials was very encouraging. 



There are many possible applications of thermocouple psychrometers to research 

 problems in all areas of the environmental sciences; only a few applications are 

 described here. In research on physiological responses of plants under natural condi- 

 tions, thermocouple psychrometry provides the best method for determining the diurnal 

 and seasonal magnitudes of water potential gradients from the soil, through the plant 

 stem, to the leaves. Psychrometers thus permit integrated field determinations of the 

 water potential gradient throughout the soil-plant continuum. This capability has 

 application in many areas of research, including : theoretical physiology and soil physics 

 range and forest revegetation; watershed; range; forest management research; fire 

 control research; and, research in plant pathology. Thermocouple psychrometers appear 

 to be primarily useful as research tools; however, at least one application to land 

 management problems comes to mind. This application is in the area of fire-danger rat- 

 ing; the application of thermocouple psychrometers appears to offer an excellent oppor- 

 tunity for evaluating the potential flammability of live standing vegetation, ranging 

 from large tree stems to fine leaf material. This would require some preliminary re- 

 search, but the potential application is clear. There are, without doubt, other appli- 

 cations to land management problems; hopefully, the possibility of such applications 

 will stimulate the imagination of the reader. 



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