378 



PHYSIOLOGY OF GROWTH. 



chiefly used for investigation seedlings of Phaseolus grown in 

 flower-pots, in good garden earth, and with the epicotyl projecting 

 about 2 cm. from the soil. The thread can easily be fixed to the 



plant ^by a loop. The pulley 

 bears on one side the indi- 

 cator, z, and on the other the 

 arm, a, which is pierced to 

 permit the passage of the 

 thread, /, and carries a movable 

 weight, &, which serves to 

 balance the weight of the in- 

 dicator, or give a certain over- 

 weight on one side. It is best 

 to balance the indicator exactly, 

 and obtain the desired excess 

 weight by a thread suitably 

 carried over the pulley and 

 stretched by a weight. The 

 quadrant has a radius of 70 cm.; 

 the pulley, r, is small, so that 

 the growth movement is magni- 

 fied about 43 times by the in- 

 dicator, z. The indicator is a 

 tapering brass tube. The 

 quadrant can be moved up and down on the heavy iron stand, 

 e ; it must be set up in such a way as to be vibration-free, e.g. 

 on a bracket fixed to a massive wall. 



For many purposes it is very desirable, and indeed often 

 essential, in accurate researches on growth, to have apparatus for 

 automatically registering the growth. Sachs 1 was the first to 

 construct an instrument for the purpose, viz. the self-registering 

 auxanometer. After him Wiesner, Baranetzky, Pfeffer, 3 and 

 others described modified forms of apparatus, and perhaps the 

 most serviceable is that of Pfeifer, which may be obtained of 

 .Albrecht, Tubingen, at a price of 320 marks. For success in the 

 experiments it is naturally an important condition to have the 

 apparatus set upon a table free from vibrations.* The thread 



* The instrument here described and figured is the same as that mentioned 

 by Pfeffer in his handbook. Recently the auxanometer has been still further 

 improved in some respects by Pfeffer, and the newer form may be obtained at 

 the same price from Tubingen. 



FIG. 12 i. Auxanometer. (After Pfeffer. ) 



