BRIGGS AND SHANTZ: WILTING COEFFICIENT OF PLANTS 229 



of a deficiency in the soil moisture supply. By a permanent 

 reduction in the moisture content is meanl a condition from which 

 the leaves can not recover in an approximately saturated atmos- 

 phere without the addition of water to the soil. In the case of 

 most plants, wilting accompanies the reduction of the water 

 content of the leaves, and is the criterion used to determine the 

 wilting coefficient of a soil for that plant, The definition, as 

 stated, is applicable also to those plants which, owing to struc- 

 tural peculiarities, do not give visible evidence of a reduction of 

 the moisture content of the leaves. The wilting coefficient 

 for such plants is determined by means of the balancing method. 

 In making wilting coefficient determinations the following 

 precautions are necessary: 



1. The soil used should be as uniform as possible. 



2. The soil should be brought to a uniform water content before 

 being used. 



3. All loss of water should be prevented except that due to the tran- 

 spiration of the plant. 



4. All sudden fluctuations in temperature should be avoided. 



5. The moisture determination should be made as soon as the plant 

 has first reached a wilted condition from which it can not recover when 

 placed in a damp chamber. 



The method employed consists in growing the plants in a small 

 glass pot, evaporation from the soil surface being prevented by 

 means of a seal of wax which is melted and flowed over the soil 

 surface. In the case of monocotyledons, this wax seal can be 

 applied immediately after planting the seeds, and the seedlings 

 will grow readily through the wax, which forms a perfect seal around 

 the stems. In the case of dicotyledons, the wax, which is usually 

 a mixture of paraffin and petrolatum having a low inciting point 

 and low heat conductivity, can be melted and flowed around the 

 stems of the seedlings without injury. During growth, the pots 

 are kept immersed in a water bath to avoid condensation of the 

 soil moisture on the pot walls. 



\Vhen the precautions noted above are observed, the probable 

 error of the mean of the determinations from twelve pot> docs 



