Chap, ii.] OF MOVEMENTS IN THE VEGETAL KINGDOM. 345 



are the Dioncea muaevpula, the Oxalis sensaiiva of Java, and the 

 Mimosa pudica. The leaves of the dionsea are furnished with 

 true darts, which transpierce the insects as soon as they come in 

 contact with them. As to the OasaUs sensitive, its mode of action is 

 nearly like that of the Mimosa pudica, which we ^aU take as a type. 



The periodical movement is very marked in the Mim^osa pudica. 

 According to the observations of MM. P, Bert and MiUardet^ it 

 is efEected thus. In the evening the petiole of the compound 

 leaf is much lowered ; then it begins to rise again towards mid- 

 night, consequently without any luminous excitation, and before 

 simrise it has attained its maximum of uprightness. At sun- 

 lise it begins to lower itself very rapidly, whilst the folioles 

 separate and spread themselves out. At the commencement of the 

 night, the petiolaay depression is at its maximum, and the folioles 

 are close to the petiole. But, in addition to this slow periodical 

 movement, the leaf has extreme sensitiveness, and all contact, 

 all mechajiical or chemical irritation, causes it instantly to 

 assume its nocturnal position. 



It is towards 30 degrees that the sensitiveness of the mimosa 

 pvdica attains its maximum. Below 15 degrees it is null. At 

 40 degrees the folioles become rigid in an hour, at 45 in half-an- 

 hour, from 48 to 50 in a few minutes. Up to this point they 

 may still recover their sensitiveness in a lower temperature, but 

 at 52 degrees they lose it finally. Below 15 degrees, or after 

 having remained some days in darkness, the folioles also become 

 rigid, but transitorily.^ 



llngenhGuz and Humboldt have seen the motility of the sensitive 

 plant disappear when the plant was plunged into carbonic acid, 

 azote, &c., but this was only because it could no longer respire. 

 On the contrary, they have seen it naturally persist in oxygen. 

 An electric current causes the depression of the leaves. On the 

 contrary, cMoroform and ether abolish the piotility. 



1 Bert, Becherches swr Us Mouvements de la Sensitvve. Paris, 1867. 



2 Sachs, loc. cit., p. 855, 1035, 1037 ; and Dutroehet, Mimoires pour senir, 

 &o., t. I. p. 524. 



