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"1 CO .' ~- ("~) C~ practice, species are sought that are water inefficient. The C) greater the number of small stomata, the larger will be the exposable evaporative surface area. Similarly. the larger, better developed, and more active the root area, the larger will be the abso~ptive surface fo~ water uptake, Therefore, species having a large number of small, densely packed stomata and a large root-shoot ratio a~e desired, Environmental factors determine the extent to which the capacity of a particular species is utilized, Light is required for stomata to open, Thus, locations having long day-length during the growth season can be expected to favor extended transpiration, Large diffusion pressure deficits are desirable, since diffusion pressure deficit influences both wate~ abso~ption and evaporation, Water is absorbed by roots because a diffusion p~essure deficit gradient exists between the soil solution and the cytoplasm of the interior root cells. If the salt concentration, or osmotic pressure, within the soil is greater than within the root cells, water will flow from the plant to the soil, Thus, conditions conducive to maintaining low soil salinity, or avoiding salt build-up, are desirable. This suggests that the soil substrate be highly permeable and have a low ion exchange capacity so that salts, concentrated by transpiration. can pass out of the root zone, This also indicates that species able to tolerate high internal salt concentrations will ~ikewise be able to concentrate salts more throughly, Similarly, since internal atmosphere of a leaf can usually be considered to be saturated with water vapor, the ~ate of evaporation will be influenced by the water vapor content, or relative humidity of the air. The lower the humidity, the steeper the gradient and the more rapid the rate of transpiration. This suggests that the more arid the climate, the more effective the STEP process will be; thus, either high altitude o~ desert areas are sought. This assumes, of course, that the aperature of the stomata opening is the same unde~ all conditions. Wilson (1948) found that temperature could influence the degree of aperature opening, In cotton leaf. fo~ example, stomata we~e closed at o leaf temperatures approaching 0 C, would open progressively wider until a maximum was achieved between 250C - 30oC, and began to close as leaf temperatures were forced higher, The ideal environment for the STEP process will include a warm but not excessively hot growth season, although this will be heavily influenced by evaporative cooling from both the leaves and the g~owth pond surfaces. Wind will influence transpiration by constant turnover of air. maintaining the diffusion pressure deficit, and cooling leaf surfaces through the latent heat of evaporation, The increase in t~anspiration is not proportional to wind velocity, Speeds 17.