2o Elementary Plant Physiology. 



consisting of a lever to which a small pulley is attached by the 

 pin or needle used as pinion. The ends of the needle rest 

 in bearings at the end of a horizontal support attached to a 

 stand, and the thread from the plant runs over the pulley, and 

 a weight is attached to its end (Fig. 9). 



The greatest possible delicacy may be secured by the con- 

 struction of a mirror auxanometer as follows : 



Secure a small microchemical balance with the arms of the 

 beam about six to nine centimeters long. Remove the upright 

 standard, bearing the beam, from its base, and fasten rigidly to 

 the upper surface of a block of wood by means of screws. Re- 

 move the scale pans and their swinging supports. Bore a hole 

 longitudinally half way through a cylindrical cork stopper which 

 is about three centimeters in diameter, and fit over the end of 

 the scale beam. Fasten a small plane mirror, four centimeters 

 in diameter, to the other end of the cork, by means of glue or 

 sealing-wax, in such manner that its surface is at right angles to 

 the long axis of the beam. With asphalt-black make a large 

 round dot in the center of the mirror, or draw a heavy black 

 horizontal line across the face. Next procure a strip of heavy 

 white paper, five-centimeters in width and two meters long, 

 and rule it into two centimeter intervals with heavy black 

 lines. Fasten this strip to an upright support of wood, and 

 place at a distance of five to ten meters from the mirror, and 

 facing it. Attach a plant to the free end of the lever, as 

 above, and add weights to the same arm to prevent too great 

 stretching of the stem. Now set up a board or a pasteboard 

 box at a distance of about two meters from the mirror, a short 

 distance to one side of a line run from the mirror to the paper 

 scale. Make a small aperture in the board or box, through 

 which the reflection of the scale may be seen in the mirror. 

 Some shifting of the scale, instrument, or peepsight will be neces- 

 sary to get the whole apparatus in order. Note the exact divi- 

 sion of the scale visible over the dot or line on the mirror. 



