A PRECISION AUXANOMETER AND ITS USE 291 



tion to measure accretions in growth of no more than a millimeter 

 weekly with reliable results, and is far steadier for all purposes than 

 any which have been described so far, and was designed by the 

 author to take observations upon such forms as the slow growing 

 succulents, and plants kept for long periods in darkness. It may 

 be kept in action for a week with no attention whatever. This 

 instrument is furnished with a cylinder 9 cm. in diameter and 9 

 cm. in height which is kept in continuous motion by a clockwork 



FIG. 139. Precision auxanometer attached to leaf of Hyacinthtts Belgicus. A 

 small metal clamp engages the tip of the leaf, and a thread attached to the clamp passes 

 up to a sleeve attached to the outer arm of the lever The actual amount of growth 

 is magnified 45 times when the instrument is arranged as above. The thread has been 

 shortened and the pen is in contact with the paper on the lower part of the cylinder 

 as at the beginning of the experiment. The cover under the stand may be used to 

 protect the cylinder and mechanism from dust and moisture. The pot containing the 

 plant rests upon a plate which may be lowered or raised by the action of a screw ; 

 when the growth of the plant allows the pen to reach the top of the cylinder the plate 

 is lowered at once to start a new tracing near the lower edge of the paper, without 

 handling the plant or readjusting the clamp or fastenings (See Fig. 142). 



