DARWIN ON THE MOVEMENTS OF PLANTS. 509 



shown at A and B (Fig. 12), where the leaves ai'e seen at night crowded 

 together, as if for mutual protection. Not less striking is the con- 

 trast between the night and day aspect of Cassia coi'ymbosa, as seen in 

 Fig. 13. Here the horizontally extended leaflets sink down vertically 

 at night, and at the same time rotate so that the lower surface faces 

 outward. 



A. B. 



Fig. 13. CA38IA cortmbosa : A, plant during day ; B, same plant at night. 



from photographs. 



Both figures copied 



As a conclusion from all his experiments, observations, and reflec- 

 tions upon this subject, Mr. Darwin states . 



" The great sweeps made by the stems of twining plants, and by 

 the tendrils of other climbers, result from a mere increase in the am- 

 plitude of the ordinary movement of circumnutation. The position 

 which young leaves ultimately assume is acquired by the circumnutat- 

 ing movement being increased in some one direction. The leaf -blades 

 of various plants assume a vertical position through modified circum- 

 nutation, in order to protect their upper surfaces from being chilled 



