82 



EXPERIMENTS WITH PLANTS 



of a student -lamp chimney (size No. 1) 

 containing several corks (small enough 

 to slide easily in the chimney) fastened 

 together end to end by means of sealing- 

 wax. In the enlarged base of the chim- 

 ney a large cork or wooden disk is fitted, 

 through which passes a clothes-pin of 

 the sort indicated in the figure. Through 

 the wire coil in the clothes-pin passes a 

 wire nail, which is firmly held in place by 

 two wire loops, which are securely fast- 

 ened to the narrow neck of the chimney; 

 another wire is passed around the chim- 

 ney just below the nail, to hold the wire 

 loops in position. A stopper is inserted 

 in the end of the chimney and water 

 poured in. A Horse-bean with a caulicle 

 about a quarter of an inch long is inserted 

 in the clothes-pin, which is then firmly 

 wedged into the cork (a small wooden 

 wedge may be used if necessary), and 

 placed in such a position that the tip of 

 the caulicle rests in a small excavation in 

 the center of the topmost cork. If the 

 pressure of the cork float is so great as to 

 break or injure the root, stick a pin into 

 the topmost cork in such a way as to 

 temporarily remove the pressure from the 





69. Apparatus for 

 determining how 

 much force the 

 root exerts in 

 growing down- 

 ward. The root 

 depresses the 

 cork float. 



