76 CARNEGIE INSTITUTION OF WASHINGTON. 



Auto-Irrigation of Pots of Soil for Experimental Cultures, by B. E. Livingston. 



As has been reported, the porous-cup auto-irrigator furnishes a means 

 for automatically maintaining the water-content of a given soil mass 

 very nearly uniform for long periods of time, and it allows the ready 

 measurement of the rate at which water is absorbed by the soil mass in 

 question, as this rate fluctuates with the rate of water-loss b}^ plant 

 transpiration or by direct evaporation from the soil surface. With 

 small amounts of soil and small plants one or more of the 12.5 cm. 

 cylindrical cups used in the porous-cup atmometer have proved satis- 

 factory, but the joining of a number of these small cups together, so 

 as to avoid possibihty of air-leakage, is somewhat uncertain, so that 

 larger cylinders were desirable. These have now been obtained, the 

 new size being about 5 cm. in diameter and 35 cm. long, thus allowing 

 the use of a much deeper pot for the plant cultures than has heretofore 

 been possible, without burying the stoppered opening in the soil. 

 Placed horizontally, these larger porous cylinders furnish a satisfactory 

 means for automatically maintaining the soil-moisture content in 

 shallow culture-boxes. 



The Progress of Wilting as Indicated by Foliar Transpiring Power, 

 by A. L. Bakke and B. E. Livingston. 



By means of the method of standardized cobalt chloride paper (a 

 modification of the method of Stall) the march of foliar transpiring 

 power was determined during progressive wilting of the plant. As the 

 water-content of the plant decreases, foliar transpiring povrer decreases 

 also, but as temporary wilting occurs and becomes more pronounced 

 the rate of decrease in transpiring power becomes less rapid. At about 

 the time when permanent wilting (in the sense of Briggs and Shantz) 

 is attained, the value of the index of fohar transpiring power suddenly 

 increases markedly, soon attaining a secondary maximum and then 

 finally falling to zero, as the leaves die and desiccate. This secondary 

 maximum in foliar transphing power, as wilting progresses, has been 

 pointed out by Leclerc du Sablon and others, though not in exactly 

 this connection. Its detection by means of hygrometric paper may be 

 of value in determining when permanent wilting actually" occurs, or 

 the occurrence of this secondary maximum may be taken as a criterion 

 for detecting the physiologically critical point for which permanent 

 wilting has been an approximate criterion. 



Foliar Transpiring Power and the Darwin and Pertz Porometer, 

 by S. F. Trelease and B. E. Livingston. 



The direct method of measuring the transpiring power of leaves by 

 means of standardized cobalt-chloride paper was employed in a study 

 of the diurnal march of this physiological condition in leaves of wan- 

 dering Jew (Zehrina) grown in the greenhouses of the Laboratory of 



