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<br />- <br /> <br />. <br /> <br /> <br />O('?O~'q <br />) ," (" ' <br /> <br />2. Measurements to give more direct indications of transpiration <br /> <br />by the different kinds, sizes, and arrangements of trees <br /> <br />growing in the various situations found in the field. New <br /> <br />tools are now available. Nuclear methods for sampling soil <br /> <br />moisture greatly increase ease and accuracy of comparing <br /> <br />moisture extraction by plants. Even more promising are <br /> <br />methods of measuring rate and amount of sap ascending in <br /> <br />plant stems. <br /> <br />3. More attention to the biological controls of transpiration. <br /> <br />The physical determinants of transpiration have and are <br /> <br />receiving most of the attention. Yet we are aware that <br /> <br />there are great differences among plants in efficiency of <br /> <br />extracting moisture from the soil; in moving moisture from <br /> <br />root to leaf; in operation of stomates; in internal leaf <br /> <br />area; and in resistance to drying. <br /> <br />4. The relationship of water use to specific site situations <br /> <br />is receiving attention. More direct measurements of <br /> <br />transpiration combined with more information about soil <br /> <br />depth, soil moisture, and ground water conditions seems <br /> <br />to locate key situations on a watershed where changes in <br /> <br />plant cover may be most useful. <br /> <br />Usable yie1d.--Water yielded during flood periods is normally less <br /> <br />useful than water yielded at other seasons. There are exceptions where <br /> <br />abundant storage is available and flood risk is slight. In many sections, <br /> <br />- 8 - <br />