292 GROWTH 



over which it rests. The clockwork is attached to a cast-iron 

 plate 1 3 cm. wide and 27 cm. long which also serves to support 

 the levers. The cylinder is provided with sheets of paper of 

 sufficient width held in place by a vertical metal strip which enters 

 a slot in the rim attached to the lower end of the cylinder, and 

 clamps the upper edge of the shell of the cylinder. The sheets 

 of paper provided for this instrument are specially ruled with 

 straight horizontal lines 1.5 mm. apart, and transversely to these 

 with curved lines 2 mm. apart, having a radius equal to the arm 

 of the lever which carries the pen. An aluminum lever 5 mm. 

 in width is carried by pin-wheel bearings between two upright 

 posts. The long arm of this lever is 1 5 cm. in length and carries 

 a swinging aluminum pen which prevents any undue friction upon 

 the paper, for which also a further regulating device is provided. 

 The short arm of the lever may be varied in length from 5 mm. 

 to 2 cm. and is attached to the short arm of a second lever, the 

 free end of which projects beyond the general outline of the ap- 

 paratus. The two arms of this lever have the relative lengths of 

 one to three, and the plant may be attached to any point on the 

 free arm by means of a loop attached to a slide. The short arm 

 of the last lever is weighted so that the pen rests at the upper 

 edge of the paper when not attached to a plant. When the tip 

 of a plant is attached to the free end of the lever by means of a 

 cord and clamp as in the previous experiment, the cord is shortened 

 until the pen is in contact with the lower edge of the paper, or 

 near it. The actual contact of the pen is prevented by a small 

 rod until the instrument is properly adjusted. When all is in 

 readiness the pen is allowed to come in contact with the paper 

 and the extension of the plant allows the pen to rise, tracing an 

 irregular line as shown in Fig. 142. The curved lines are such 

 distances apart that the interval between two of them is carried 

 past the pen in two hours. The horizontal lines being 1.5 mm. 

 apart the amount of movement of the pen upward during the two 

 hours may be easily read off, and plotted. The tracings being 

 made with ink are permanent and may be filed for reference, and 



