56 BOTANICAL GAZETTE [yuLy 
latter case the cylinder makes a complete revolution in about four 
days. A strip of ordinary millimeter cross-section paper is used 
for the record sheet. In class experimentation this recording 
clock has a variety of possible uses aside from this particular 
experiment. 
Fic. 2.—Weight dropper and circuit-closing device 
THE WEIGHT DROPPERS.—As in the Ganong transpirograph, the 
recording of the water losses depends upon an electrically actuated 
mechanism which drops a definite weight in the form of a one- 
fourth-inch ball upon the scale pan whenever the pan reaches a 
certain height. As shown in fig. 2, the circuit-closing device 
consists of two platinum points just beneath the delivery tube 
