50 



WILTING COEFFICIENT FOE DFFFEEEXT PLAXT; 



bound with nrie wire to the outside of the glass and cemented as 



shown, to serve as a support for the counterpoise. TThen suspended 

 between suitable supports the system oscillates about its position 

 of equilibrium, which can be adjusted by means of the counter- 

 poise. The end of the counterpoise rod in this case serves as an 



Fig. 4.— Simple apparatus for determining the wilting coefficient for plants which have no sharp wilting 

 point. Knife-edges are employed which render the system much more sensitive than the one shown in 

 figure 3. 



index. A vertical rod for changing the sensibility, while conven- 

 ient, is not necessary in a small system of this kind, as this adjust- 

 ment can be quite readily made by warming the cement and moving 

 one end of the supporting rod slightly. In the apparatus shown a 

 weight of 1 gram applied at the center of the pot produced a deflec- 

 tion of 20 millimeters at the end 

 of the pointer, so that a change 

 in the moisture content amount- 

 ing to 0.1 gram was readily ob- 

 served. This sensibility can be 

 increased by the use of knife- 

 edges as in figure 4. 



Another form of the apparatus 

 is shown in figure 5. Two nar- 

 row slots are milled halfway 

 through a piece of i-inch square 

 steel, so as to engage the opposite 

 walls of the glass pot, and a rod 

 for adjusting the sensibility of 

 the system is inserted in the cen- 

 ter. In attaching the knife-edges 

 to the pot the slots and the 

 edges of the pot are coated with hot cement and forced together. 



A convenient counterweight is shown in figure 6= The coarse 

 adjustment is made by sliding the counterweight along the sup- 

 porting rod, after which it is clamped by the set screw. Exact 



230 



Fig. 5.— Diagram showing the construction of knife- 

 edges. The square rod is milled halfway through 

 at points where it engages the walls of the pot in 

 order to reenforce the cement joint. 



