CHAPTER II. 



OF MOVEMENTS IN THE VEGETAL KINGDOM. 



shall first of all set aside, as foreign to our subject, the 

 slow insensible movements of the stems and roots, which depend 

 upon development, growth, &c., and whence result, for example, 

 the direction of the stems towards the sky, of the roots into the 

 soil, the spiral twisting of certain stems, &c. 



On the contrary, the movements of certain species of confervse 

 strongly recall those of animals. In fact their filaments balance, 

 lower, raise themselves, twist themselves, and oscillate ; and so 

 on. Heat and light accelerate them ; cold and darkness retard 

 them. Acids, alkalis, alcohol, &c., suppress them. 



We have already pointed out the movements of the spores and 

 of the antherozoids. In a number of phanerogamic species, the 

 various parts of the flower execute extended movements. Certain 

 flowers open in the day and shut in the night, or inversely. 

 This phenomenon even takes placfe habitually, in each species, at 

 a certain hour, so that by choosing suitable species, Linnaeus could 

 form what he called Fiords clock. 



The movements of the petals depend much upon heat and light. 

 It is only between 8 and 28 degrees that the flower of the crocus 

 opens. Below this it does not open at all ; above, it shuts. At 

 a constant temperature, any abrupt variation of light tends to 

 decide the blowing of the flowers of the crocus, the tulip, and of 

 compound flowers ; every abrupt diminution tends to close them. 



In cellars, lighted at night by lamps, and kept in darkness 



