i8o 



PLANT LIFE. 



be studied by direct observation with a microscope, but more 

 conveniently by magnifying the growth by mechanical means, 

 so as to observe the movements of a pointer over a scale. 

 Such an instrument is an auxanometer. Those forms of it 

 which secure a continuous record automatically are of the 



FIG. 182. Golden's auxanometer. The instrument consists of two parts, a multiplying 

 pulley and two recording rods turned by a clock. A thread from the plant passes 

 through a bent glass tube and makes one turn around the small pulley to which it is 

 then fastened. Another thread makes one turn around large pulley and descends 

 to carry a pointer which slides on two guide rods. As the plant grows the thread 

 from it slackens and the pointer descends at a magnified rate by its own weight. Two 

 glass rods, blackened in a smoky gas-flame, are rotated by a clock to whose hour- 

 spindle the frame carrying them is attached. As they pass the pointer a mark is made 

 on the smoked surface. The distance of the successive marks shows the amount of 

 growth as magnified. Permanent record may be made by means of blue prints, using 

 the rods (which are removable) as negatives. After Arthur. 



most service (fig. 182). By imperceptible gradations these 

 cells pass into the third and final stage of growth, which is 



