METHOD OF BALANCE 23 



is here secured with ease and certainty ; the apparatus 

 has an attached scale which indicates the actual rate of 

 growth, and the upsetting of the balance by a stimulant 

 or a depressor is automatically recorded. 



Principle of the Method of Balance 



The plant is made to descend at the exact rate at which 

 its growing tip is rising : the latter is attached in the usual 

 manner to the High Magnification Crescograph. When 

 growth is exactly balanced, the record is a horizontal line 

 instead of an ascending curve as in the ordinary method. 

 The apparatus so adjusted is found to be extremely sensitive. 

 The minutest change induced in the rate of growth by the 

 environment is at once indicated by the upset of the balance 

 and recorded as an up- or a down-curve. 



The compensating movement of descent. — A regulating 

 contrivance had to be devised for the subsidence of the 

 plant at the same rate as its growth-elongation. The re- 

 quired method is somewhat analogous to the compensating 

 device for an astronomical telescope, which neutralises the 

 effect of the earth's movement round her axis once in 

 24 hours. The problem is, however, far more difficult ; 

 for instead of compensating for a definite rate, adjustments 

 had to be made for balancing widely varying rates of 

 growth of different plants, and even of the same plant under 

 different conditions. The problem w^as solved by the 

 employment of two different methods of compensation : 

 A, the Method of Falling Weight, and B, the Method 

 OF Inclined Plane. 



A. Method of Compensation by Falling Weight 



By means of a train of revolving clock- wheels actuated by 

 the fall of a weight, the plant is made to subside at the same 

 rate as that at which it is growing.^ It will be presently 

 explained how the gradual turning of the adjusting screw S in 

 a right-handed or a left-handed direction causes a continuous 



^ Life JMovements in Plants (1919), p. 257. 



