128 PLANT RESPONSE 



Summary 



The principal types of response seen in animal tissues are 

 found also in the responses of plants and of inorganic 

 substances. 



Three types of responses are possible : (i) that in which 

 response is proportionate to stimulus ; (2) that in which 

 response is disproportionately greater than stimulus ; and (3) 

 that in which all or part of the stimulus is, for a longer or 

 shorter time, absorbed by the tissue and held latent. 



The subsequent effect of stimulus which is held latent 

 may sometimes be seen in singly ineffective stimulus which 

 becomes effective on repetition ; or in the staircase response, 

 consequent on the enhancing of molecular mobility by the 

 partial absorption of previous stimulus. 



The fact that stimulus may be held latent for a time, and 

 subsequently find expression, is strikingly shown in the 

 occurrence of multiple response, in answer to a single strong 

 stimulus. 



It is also possible for the incident stimulus to become 

 divided in its expression, part of it finding an outlet directly 

 in mechanical response, and part becoming latent, and causing 

 accelerated growth. The gradual augmentation of the latter 

 of these may cause a corresponding diminution of the former. 

 An appearance of fatigue is thus brought about, which is 

 misleading, as the decrease of mechanical response is in this 

 case due. not to a diminution, but to an increase of latent 

 energy in the responding substance, as shown by its capacity 

 for renewed growth. 



