SENSITIVE PLANTS. 297 



much more strongly marked than in older specimens, * 

 seedling plants and babies being both remarkable for 

 the length and soundness of their slumbers. 



Now, in many of the Mimosse, and in some of the 

 Acacise, these sleep movements are specially clearly 

 defined, for upon the approach of evening, their foliage 

 is seen to become closely folded up, and to open again 

 at sunrise on the following morning. A number of 

 curious experiments were made by De Candolle with 

 the sensitive plants (Mimosa Pudica, and Mimosa 

 Sensitive), and it was found that they could be put 

 to sleep, like babies, almost at will, for plants removed 

 from daylight to darkness quickly fell asleep while 

 others, exposed for several nights in succession to 

 artificial light, and kept in darkness by day, accustomed 

 themselves to their new conditions, " opening their 

 leaves in the evening, and closing them again in the 

 morning at the hour when their night commenced." 

 In the case of other sensitive plants deprived of light 

 altogether, it was found that the alternations of sleep- 

 ing and waking still went on, but became very 

 irregular, f 



The sensitive plants, of which there are several 

 varieties, as we know, are so called from the curious 

 fact that they are exceedingly sensitive to anything 

 touching them ; and in Ceylon and some of the Brazilian 

 forests, where the Mimosa Pudica is a common weed, 

 many square yards covered with these plants may be 

 seen instantly to shrivel up, exactly like a living 

 creature in pain or fear, when anyone treads upon its 



* Histoire des Plantes, by Louis Figuier, p. 109. 

 t Ibid., p. 112; see also Encycl. Brit. Vol. xvi, p. 345, 9th edit., 

 article "Mimosa." 



