CHAP, in.] the Movements of Plants. 541 



majority of writers, in accordance with the tendencies of the 

 age, professed their desire to refer the phenomena of life in 

 plants not to an unknown principle called the soul, but to 

 mechanical and physical causes ; but they did not apply their 

 minds to the examination of these phenomena with that stren- 

 uous effort, which in this subject especially could alone lead to 

 a complete and satisfactory explanation of them. 



Linnaeus studied the periodical movements of flowers in 

 1751 and those of leaves in 1755, but a mechanical explanation 

 of them was not to be expected from him ; he contented him- 

 self with pointing out the external conditions of these phe- 

 nomena in many species, with classifying them, and giving the 

 periodical movements a new name by calling the positions 

 assumed by night the sleep of plants ; nor did he use the word 

 at all in a metaphorical sense, for he saw in this sleep of 

 plants a phenomenon entirely analogous to sleep in animals. 

 That the sleep-movements were not capricious but due to 

 external influences was with him a necessary consequence from 

 the nature and idea of the plant, which was that of a living and 

 growing being, only without sensation. But it should be men- 

 tioned that he stated correctly that the movements connected 

 with the sleep of plants are not caused by changes of tempera- 

 ture, or not by these only, but by change of light, since they 

 take place in the uniform temperature of a conservatory. 



Linnaeus' account of these kinds of movement was only 

 formal, it is true, but still it was well-arranged and clear ; the 

 treatment of the same and other movements by his contem- 

 porary Bonnet was quite the reverse. It is scarcely possible to 

 imagine anything more shapeless, such an utter confusion of 

 things entirely different from one another, as is to be found in 

 Bonnet's experiments and reflections on the various movements 

 of leaves and stems in his work on the function of leaves, pub- 

 lished in 1754; geotropic and heliotropic curvatures, nutations 

 and periodic movements, are all run one into another; a 

 person who understands something of the subject may find 



