i8o 



PLANT LIFE, 



be studied bv direct observation with a microscope, but more 



conveniently by magnifying rlie growth l)y mechanical means, 

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

 Such an instiument is an auxanometer. 'i'hose forms of it 

 which secure a continuous record automatically are of the 



Fig. 1^2. — C'rolden's auxaimnK-lcr. 'riit; iiistriinicnt (.(insists nf two parts, a multiplying 

 pulley and two recording rods turned by a clock. A tlircid frnm tlie plant passes 

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

 then fastened. Another thread makes one turn artiund 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 t(t whose hour- 

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

 on the smoked surface. The distance of the successi\e marks shows the amount of 

 growth as ma,t;;nified. Permanent record may be made by means of blue prints, using 

 the rfids (which are removable) as negatives. — After Arthur. 



most service {fig. T82y By imperceptible gradations these 

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



