Researches on Growth and Movement in Plants. 



367 



thin layer of smoke. As the recording lever is about 40 cm. in length, the 

 curvature in the record is slight, and practically negligible in the middle 



m. , 











i 





i 



\L 



L 



c 





p 



L 



^ 



m 



Fig. 1. — Compound lever. P, plant attached to short arm of lever, L ; T, weight exerting 

 tension ; C, connecting link ; L', second lever with ' bent tip for tracing record. 

 BB, balancing countei'poise : Fork, F, carrying on its sides two conical agate cups, on 

 which lever rests by two pin-points. 



portion through a length of 4 cm. The dimensions given allow a magnifica- 

 tion of 10,000. A far more compact apparatus is made with 15 cm. levers. 

 This gives a magnification of 1000. 



Connecting Links. — Another puzzling difficulty lay in the fact that the 

 magnification actually obtained was sometimes very different from the 

 calculated value. This unreliability I was able to trace to the defects 

 inherent in the tliread-connections at first employed to attach the plant to 

 the first lever and the first lever to the second. These flexible connections 

 were found to undergo variable amounts of elastic yield. Hence it became 

 necessary to use nothing but rigid connections. The plant-attachment. A, of 

 triangular shape is made of a piece of navaldum ; its knife-edge rests in a 

 notch on the short arm of the lever, L. There are several notches at various 

 distances from the fulcrum. It will be understood how the magnification can 

 be modified by moving A nearer to or further from the fulcrum. The lower 

 end of the attachment is bent in the form of a hook. The end of the leaf of 

 the plant P is doubled on itself and tied. The loop thus formed is then 

 slipped over the hooked end of A. 



The Hnk, C, connecting L and L' (fig. 1) consists of a pin pointed at both 

 ends, which rests on two conical agate cups fixed to the upper and lower 

 surfaces respectively of the levers L and L'. This mode of frictionless 

 linking is rigid and allows at the same time perfectly free movement of the 

 levers. 



