Recent investigations at the University of California have yielded much information regarding the relation of soil moisture to the normal growth and behavior of fruit trees, and have indicated serious disagreements with results secured by some previous investigators of the problem of water relations of plants. It is logical to suppose that the moisture conditions of the soil do not exert any direct retarding influence on the plant so long as water is supplied to the absorbing surfaces of the roots and is conducted to the leaves as rapidly as required by the transpiration rate. However, just as soon as the rate of supply falls below this requisite amount, then soil moisture becomes a limiting condition. An inadequate moisture supply may be evidenced by lessening of turgor, cessation of growth, and wilting, and, in more advanced stages, by death of the tissues. Of course, the wilting of a plant does not indicate that water has ceased to move from the soil into the plant, but simply that transpiration has exceeded absorption and conduction. It is obvious, since wilting is progressive, that various stages of wilt might be recognized. Several attempts have been made to fix upon a definite degree of wilting. The "saturation deficit" of RENNER (6) and the "incipient drying" of LIVINGSTON and BROWN (4) are not definite stages, but represent broad ranges in the progress of wilting, but the "permanent wilting" of BRIGGS and SHANTZ (1) represents a fairly definite stage or degree of wilting, which can be readily recognized in experimentation, and this has received much study. However, KOKETSU (3) has pointed out that definite stages of wilting may be recognized readily in Mimosa because of the movements of its leaves.BRIGGS and SHANTZ defined their permanent wilting as that stage. of wilting when the leaves first undergo a permanent reduction of their moisture content as a result of deficiency in th-esoil-moisture supply. A permanent reduction is here taken to mean a deficiency in leaf-water content from which the leaves do not recover in an approximately saturated atmosphere, without the addition of water to the soil. LIVINGSTON and KOKETSU (5) have further discussed the condition of permanent wilting and have emphasized the dynamic nature of the wilting process.BRIGGS and SHANTZ (1) concluded from their studies that atmospheric environmental conditions have little or no effect upon the residual water content of the soil at the time of the beginning of permanent wilting and
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