138 HOFMEISTER'S EXPERIMENT. [CH. v 



elastic do not return to their original length, thus pro- 

 ducing a distortion of the shoot. 



To get an accurate notion of what occurs in this 

 experiment it is desirable to measure the radius of 

 (1) the curvature forcibly produced, (2) of the permanent 

 curvature remaining. This may be done with Sachs' 

 cyclometer, which consists of a number of concentric 

 semicircles drawn on a board. By applying the shoot to 

 the board, and comparing its outline with the semicircles, 

 the radius of curvature of the shoot can be approximately 

 ascertained and noted. In our laboratory we have two 

 boards, one bearing semicircles of which radii range from 

 1 to 20 cm. in length : while the radii of the arcs on the 

 other board range from 21 to 45 cm. 



(160) Hofmeisters experiment^. 



This is in principle the same as experiment 159 ; it 

 has, however, a certain classic interest which makes it 

 worth repeating. 



What is needed is a vertical turgescent shoot fixed 

 firmly at its lower end : it may be either a plant growing 

 in a pot, or a shoot fixed into a clamp by its basal end. 

 In either case the base of the shoot is smartly struck with 

 a light stick so as to produce violent curvature of the free 

 end of the shoot towards the side which is struck. The 

 consequence is the same as that in experiment 159, 

 namely, that a permanent curvature is produced in 

 consequence of the overstretching of the convex side of 

 the shoot. 



1 Bericlite d. k. Sachs. Gesell. d. Wiss. 1859. 



