ii] HABITS OF CONVOLUTA 59 



this phototonic effect is of considerable and even 

 fundamental importance to the well-being of many 

 animals and plants. 



If a green plant is placed in darkness the 

 mechanism of its growth is thrown out of gear. 

 Though it grows, and, if supplied with proper food, 

 might, for all we know, go on living indefinitely, its 

 nervous state is changed, its tone has been affected. 

 It becomes " drawn," as gardeners say, its stem grows 

 long and supple, and its leaves remain small and un- 

 developed. As, without the controlling baton of the 

 conductor, the unity of the orchestra is lost, and, it 

 may be, harmony is replaced by discord, so, without 

 the constant influence of light, the harmony of growth 

 which obtains normally throughout the plant is dis- 

 turbed. Since, therefore, light-stimuli contribute to 

 the maintenance of the normal nervous state of the 

 plant, we say that light exerts a tonic influence. In- 

 asmuch, however, as even in the absence of light 

 the plant remains alive and capable of some sort 

 of growth and development, we must conclude that 

 the state of tone in which it lives is not the result 

 of light but that it is modified by light. This 

 effect of light in modifying to the advantage of the 

 organism its state of tone is called phototonus. The 

 language is clumsy but the ideas which it conveys 

 are clear enough, though lacking in precision. 



C. roscoffensis is, as we know, attuned to a high 



