IRRITABILITY OF PLANTS 139 



make up the essential progress of science. In our day 

 everywhere, and not least in India, one who can do any 

 such things on the adult scale is reckoned an ' expert ' 

 a term which again precludes further inquiry ; but the 

 inventor and the discoverer alike know themselves better, 

 and but advance in their childlike way by alternate steps, 

 not unmingled with falls, but guided by flashes of freshened 

 insight and hope. 



On such general grounds, as well as for coming to a 

 further understanding of plant-movements, it is here worth 

 the reader's while to look into this problem, of how to 

 enable the plant to make its own record of its movements 

 whether in nature or under stimulus of altered conditions. 

 For one thing, the time-relations of every phase of move- 

 ment must be found, and determined with the physicist's 

 exactitude. Though for everyday use the second hand of our 

 watches marks our ordinary limit, the starter and judge 

 of a race, or the physician feeling a pulse, have to take note 

 of fractions of a second ; hence the stop-watch, with its 

 finer graduation, down to tenths of a second. But for 

 physical measurements far smaller fractions are often 

 necessary ; hence the interest of the tuning-fork, with its 

 hundreds of vibrations per second. Better still than the 

 tuning-fork is the vibrating reed ; for of this we may adjust 

 the length to any required quickness of vibration, within 

 a wide and sufficient range, say from ten to a thousand 

 times per second. It may easily be made to write its 

 tracings on a recording surface conveniently a smoked 

 plate. The vibrating reed soon gives off its initial energy, 

 but continuous vibration may be maintained by electric 

 means. The steel reed, with its required frequency of 

 vibration once adjusted, is made to dip its bent point into 

 a small cup of mercury ; so that the metallic contact 

 should start a current which passes through a small coil 

 wire fixed above the reed, and containing a soft iron of 

 core, which the current converts into a temporary magnet. 

 The attraction of the magnet upon the reed pulls it up out 



