6 CHAP. II. HIGH MAGNIFICATION CRESCOGRAPH 



a horizontal movement by means of a mirror suitabl}^ 

 inclined. The excursion of the spot of light was followed 

 by means of a pen on a drum revolving at a known rate ; 

 or the record was obtained automatically by photography. 

 Hence a curve was obtained whose ordinate gave growth- 

 movement, and the abscissa time.^ 



Records thus obtained opened out a very extensive 

 field of investigation on growth and its variation under 

 the manifold influences of the environment. The photo- 

 graphic method is automatic, but it necessitates the 

 discomfort and inconvenience of a dark room ; the results, 

 moreover, cannot be followed visually. The other method 

 of obtaining the curve of growth by following the excursion 

 of the spot of light with a pen is far more convenient, 

 but the results in this case are likely to be affected by 

 personal error. In order to obviate all these difficulties 

 I devised a direct method, in which the plant by its own 

 autograph exhibits the absolute rate of growth and any 

 induced variation in an extremely short period of time. 



The Automatic High Magnification Crescograph 



I secured high magnification by means of a compound 

 system of two or more levers.^ The plant is attached to the 

 short arm of a lever, the long arm of which is attached to 

 the short arm of the second lever. If the magnification 

 by the first lever be m, and that by the second 11, then the 

 total magnification will be mn. 



The numerous practical difficulties encountered were 

 principally due (i) to the great tension exerted by the 

 two levers on the plant ; (2) to the possible stretching of 

 the connectors by which the plant is attached to the first 

 lever, and the first lever to the second ; and (3) to the 

 friction at the fulcrums. I will describe the most recent 

 method employed to overcome these difficulties. 



1 Plant Response (1906), p. 412. 



2 Proc. Roy. Soc, B, vol. 90 (1919). P- 3^5- 



