The Response of Plants 



139 



notice before we are in position to understand what is 

 meant by the term response, and particularly before we 

 can apply that term with accuracy in dealing with living 

 plants. The impressions from without to which our 

 senses make response are, after all, as we have lately 

 learned to know, all the result of some form of energy of 

 some form of force, perhaps of one form of energy acting 

 under different degrees of intensity. Thus the percep- 

 tion of sound is resultant upon the reception by the ear 

 of certain waves, impulses, which we may set in motion 

 and measure at our will. The perception of heat is con- 

 ditional upon impulses, similar, though vastly more re- 

 fined; the perception of light, upon waves of impulse 

 whose average length is measured in fractions of a thou- 

 sandth of an inch; but in every case touch, sight, hear- 

 ing, the sense, the cognition or recognition, is conditioned 

 upon physical impulse, upon something that can be esti- 

 mated, weighed, or measured. Now we say that our fin- 

 gers respond to the presence of heat, our ears to sound, 

 our eyes to light, and we perceive that in every case the 

 response is a result of the impact of physical force. 

 Waves beat upon the surface of our bodies and we feel 

 them ; waves beat in soft lapping measures upon the out- 

 spread auditory nerve, and we hear them; waves dance 

 in brilliant sequence on the retina of the eye, and lo! 

 we see! 



But this is only one-half the problem. A response, as 

 the idea is now growing in our minds, is two-fold in na- 

 ture. We have described only the outside half of it. As 

 the philosopher would say it is both objective and sub- 

 jective; but objectively it includes here both the cause 



