CHAPTER XLVIII 



NYCTITROPIC MOVEMENTS 



Comparison between nyctitropic and autonomous pulsations — Diurnal movement 

 of plagiotropic stem — Supposed distinction between nyctitropic and other 

 movements of response to stimulus of light — Diurnal response of leaf of 

 Biophytum — Diurnal response of primary petiole of Mimosa — Periodic 

 impulses acting on the leaf — Periodic impulses contributed by the plant as a 

 whole — Other modes of exhibition of diurnal periodicity of hydrostatic tension 

 — Forced vibration and its periodic after-effects — Physical analogue — Impressed 

 periodic vibrations in organ originally radial. 



IN addition to the other effects of light which we have been 

 studying, there is also a periodic movement, induced by the 

 alternation of day and night, which consists of a pulsation 

 executed by the responding organs in the very long period 

 of twenty-four hours. In its pulsatory character this move- 

 ment resembles the so-called autonomous pulsations of such 

 leaflets as those of Desmodium gyrans. But besides the fact 

 that it has the long and definite duration of twenty-four 

 hours, whereas the autonomous pulsations of the leaflets of 

 Desmodium are short and variable in period, there are other 

 differences between the two. 



Comparison between nyctitropic and autonomous 

 pulsations. — In the first place it will be noticed with regard 

 to the daily periodic movement that at any given time all the 

 motile organs of the same plant are going through the same 

 phase. This rhythm therefore is in a manner controlled by 

 the plant as a whole. In the case of autonomous movements 

 so called, on the other hand, the seat of rhythm is localised 

 in the motile organ of that particular leaflet whose pulsations 

 are being observed, and there is no necessary coincidence of 

 period, as between any two leaflets on the same plant. The 



