CHAPTER XXXI 



THE RECORD OF GROWTH-RESPONSE 



The simple Growth-Recorder — The Balanced Growth-Recorder — Rhythmic 

 growth-response--Growth-response and excitatory response — Law of direct 

 and indirect effects of excitation — Positive turgidity-variation as indirect effect 

 of excitation — Mechanical test — Significance of ' inner stimuli.' 



One of the most characteristic manifestations of life is 

 growth. The question then arises, whether this particular 

 manifestation is to be regarded as a distinct and specific 

 phenomenon, unlike all others, or whether it may be possible 

 to trace a connection between it and those responsive re- 

 actions with which we are already familiar. 



The occurrence, in response to stimulus, of numerous 

 growth-curvatures, sometimes positive and sometimes nega- 

 tive in character, offers us again a problem of very great 

 complexity. It is sometimes supposed that stimulus retards, 

 and sometimes that it accelerates, growth. But it is difficult 

 to understand how the same influence can produce opposite 

 effects. Then, again, there is intruded upon the problem 

 the unknown effect of ' inner stimuli.' From all these it will 

 be seen that the subject of growth and growth- movements is 

 one of extreme obscurity, and that the difficulties which 

 baffle us can only be met satisfactorily if we are able to 

 analyse and follow out, one by one, the various elements that 

 enter into the problem. 



We have seen in the Desmodium leaflet at standstill, and 

 in that of Biophytum under ordinary circumstances, that 

 when the latent energy is not excessive, we obtain a single 

 movement in response to a single stimulus. When the sum 

 total of the latent energy of the tissue, however, is above par, 



