XVII. ON A NEW ELECTRIC AUXAN03IETER 

 AND CONTINUOUS RECORDER. 



W. D. Frost. 



THE ELECTRIC AUXANOMETER. 



In undertaking recently some work on growth in thickness 

 it was found that there was no available auxanometer suitable 

 for the exact needs of the line of experiments designed. 

 Pfeffer's auxanometer was the best instrument within reach of 

 the writer, and while this is adapted for work with moderately- 

 large plants it is too cumbersome for delicate ones, as the 

 counter- weight required to overcome the friction of the pulleys 

 is sufficient to produce abnormal conditions. In the measure- 

 ment of growth in thickness of stems, fruits, etc. , it seemed 

 absolutely necessary that the whole instrument used should be 

 attached to, and suspended from the plant, to avoid any error 

 caused by movements, such as twisting or bending, due to hel- 

 iotropism or geotropism. 



To meet these conditions the only contrivance which seemed 

 possible was one in which a very small increment of growth 

 should momentaril}'' close an electric circuit by means of 

 some easily adjustable mechanism. The increment of growth 

 necessary to close the circuit being constant, successive 

 closures of the circuit could, of course, easily be registered. 



A working model was constructed upon this principle, and it 

 proved so successful that it has been put in permanent shape 

 by the instrument maker of the laboratory. It has further- 

 more seemed advisable to print here a description of it in ad- 

 vance of the results from its use in investigations now in pro- 

 gress in the laboratories for plant physiology of the University 

 of Minnesota. 



While it was originally intended for measuring growth in 

 thickness, yet it is equally efficient in measuring growth in 

 length. Its extreme lightness and delicacy make it especially 

 useful in measuring the growth of small plants, and since it is 



