CHAPTER XXXII 



THE EFFECTS ON GROWTH OF INTERNAL ENERGY 

 AND EXTERNAL STIMULUS 



Characteristics common to growth and to other forms of rhythmic response : 

 (i) Periodic groupings— (2) Effect of external stimulus in renewal of growth 

 when at temporary standstill — (3) Renewal of growth-pulsation by positive 

 turgidity-variation — (4) Effect of increased internal hydrostatic pressure — 

 (5) Effect of ascent of sap on growth —Effect of temperature on growth 

 — Comparison of various types of multiple response — Effect of external tension 

 on growth — Effect of direct application of stimulus on the growing region 

 — Similarities between motile and growth responses — Direct and indirect 

 effects of stimulus, and laws of growth. 



Having shown in the last chapter that growth is a form 

 of multiple or rhythmic response, I shall now proceed to 

 demonstrate in detail the fact that in it also are found various 

 phenomena which are characteristic of rhythmic response in 

 general. 



(1) Periodic groupings.- -In the multiple response of 

 Biophytum, and in the autonomous response of Desmodium, 

 we have noticed the occurrence of various periodic groupings, 

 the simplest of which consisted of an alternate waxing and 

 waning of the pulses. In multiple growth-responses, similarly, 

 we are able to detect such groupings, of which the simplest 

 was shown in fig. 169 (c). When a continuous series of 

 records is taken, extending over some time, these groupings 

 undergo various changes, as is illustrated in that figure, the 

 three series (a), (b), and (c) having been taken with the same 

 plant at different intervals. It will there be seen that the 

 pulse-records in (c) represent an alternate waxing and waning 

 of amplitude ; that in those of (&) the responses are small at 

 the beginning and large at the end ; and, finally, that in the 



