6ETTING ESTABLISHED 83 



caulicle; the caulicle will soon gi'ow down and press 

 against the cork. The amount of pressure may be reg- 

 ulated by the amount of water placed in the chimney. 

 The wire nail is now passed through the two wire loops 

 and the coil of wire in the clothes -pih. The clothes- 

 pin is now firmly held at two points, and may be 

 wedged if necessary. The seed should be sun-ounded 

 by moist cotton, and grooves should be cut in the 

 edge of the cork to admit air. 



On a strip of paper gummed to the outside of the 

 chimney marks should be made from time to time 

 to indicate the position of the float. When the plant 

 can depress it no further, the force exerted should be 

 measured by removing the clothes-pin, etc., and 

 depressing the float (by means of a bottle filled with 

 shot) to the lowest mark recorded on the gummed 

 slip. The pressure per square inch may then be 

 calculated, as in the case of the stem, by finding the 

 diameter of the root just back of the tip. 



Another simple apparatus may be arranged to test 

 the pressure of the root, as shown in Fig. 70. It con- 

 sists of u tube filled with earth, into which the root is 

 allowed to grow, and a larger tube into which this fits ; 

 the larger tube contains a wire spring, which is com- 

 pressed by the growth of the root. The larger tube 

 may be one -fourth of an inch in diameter: the 

 smaller tube should slide easily inside it; its edges 

 should be smoothed in a flame. It is well to break 



