Researches on Growth and Movement in Plants. 



371 



the mark is moved through, say, 1 mm. The magnified movement of the 

 other end of the lever at C is measured on a scale. By careful adjustment 



Fig. 3. — Complete apparatus. P, plant ; S, S', micrometer screws for raising or lowering 

 the plant ; C, clockwork for periodic oscillation of plate ; W, rotating wheel. 



of the distance of attachment A, from the fulcrum, the magnification of the 

 first lever is made about 100 times. The same procedure is followed to 

 obtain the magnifying power of the second lever. Final adjustments are so 

 made that the actual compound magnification obtained is 10,000 times. In 

 other cases the magnifications employed are 5000, 2000, and 1000. 



Experimental Accessories. — The soil in a flower pot is liable to be distiirbed 

 by irrigation and the record thus vitiated by physical disturbance. This is 

 obviated by wrapping a piece of cloth round the root imbedded in a small 

 quantity of soil. The lower end of the plant is held securely by the clamp 

 of the plant-holder. In order to subject the plant to the action of gases and 

 vapours, or to variation of temperature, it is enclosed in a cylindrical 

 chamber constructed of a sheet of mica. The chamber is maintained in a 

 humid condition by means of a sponge soaked in water. To study the direct 

 and after-effects of vapours and gases, the vessel N is filled with the given 

 vapour and the second vessel V with air or water-vapour (fig. 4). The plant- 



