Researches on Growth and Movement in Plants. 



369 



recording point. The rate of recession should, on the other hand, con- 

 tinuously increase from zero to maximum. The recording point will in this 

 manner be gently pressed against the glass plate, marking the dot, and then 

 gradually set free. It is only by strict observance of these conditions that 

 the disturbing effect of after- vibration of the lever can be obviated. 



This particular contrivance consists of an eccentric rod actuated by a 

 rotating wheel. A cylindrical rod is supported eccentrically, so that semi- 

 rotation of the eccentric causing a pull on the crank K (fig. 2) pushes the 



Fig. 2. — Eccentric for oscillation of plate ; K, crank ; S, slide ; P, holder for glass 

 plate G; A, adjusting screws ; L, recording lever. Clock releases string, C, for 

 lateral movement of the plate. 



plate-carrier gradually forward. On the return movement of the eccentric, a 

 light antagonistic spring makes the plate recede. The rate of movement of 

 the crank itself is further regulated by a revolving wheel which is released 

 periodically by clockwork at intervals of 1, 2, 5, 10, or 15 seconds respectively, 

 according to the requirements of the experiment. The complete apparatus 

 is shown in fig. 3. 



I used at first a pair of parallel eccentrics, but in the newest type of 

 apparatus with improved to-and-fro sliding arrangement, one eccentric is 

 found to be quite sufficient. A very important condition for success is the 

 securing of perfect smoothness of movement during the oscillation of the 

 plate. A horizontal slide, moving on ball-bearings, carries the vertical plate- 

 holder. The slide is so perfect in action that a puff of air is by itself 

 sufficient to move the free plate-carrier either backward or forward. The 

 plate may thus be maintained in its to-and-fro oscillation with very little 

 expenditure of force, and the power drawn from the wound-up clock is 



