l6 CHAP. II. HIGH MAGNIFICATION CRESCOGRAPH 



In the record given / = 9*5 mm., m = 10,000, t = 1 second. 

 Hence rate of growth 



= ^ ^ X 10^ LL per second = o -95 ll per sec. 



lOOOO 



I will now give a few typical examples of the employ- 

 ment of the Crescograph for the investigation of growth ; 

 the first example demonstrates the influence of temperature. 



Experiment 2. Effect of lowering the temperature. — The 

 specimen employed was Kysoor, and the record was taken 

 on a moving plate. The first part of the curve represents 

 the normal rate of growth ; moderate coohng produced a 

 diminished slope of the curve (fig. 5), demonstrating the 

 retardation of growth induced by cold. 



Precaution against Physical Disturbance 



Experiment 3. — There may be some misgiving about 

 the employment of such high magnification ; it may be 

 thought that the accuracy of the record might be vitiated 

 by physical disturbance, such as vibration. In physical 

 experimentation far greater difficulties have been over- 

 come, and the problem of securing freedom from vibration 

 is not at all formidable. The whole apparatus needs only to 

 be placed on a heavy wooden bracket screwed on to the wall 

 to ensure against mechanical disturbance. As an additional 

 precaution, a thick sheet of felt is interposed between the 

 base of the Crescograph and the surface of the bracket to 

 function as a shock-absorber. To what extent this freedom 

 from mechanical disturbance has been realised will be found 

 from the inspection of the first part of the record in fig. 6, 

 taken on a moving plate. A thin dead twig was substituted 

 for the growing plant, and a perfectly horizontal record not 

 only demonstrated the absence of growth-movement but 

 also of all disturbance. There is also another element of 

 physical change, against which precaution has to be taken 

 in experiments on variation of the rate of growth with 



